I'm trying to help my buddy fix his daughter's Camaro. It overheated and melted the valve springs and piston rings (yeah, it got that hot) a couple years ago so he replaced the motor. It overheated because the cooling fan stopped working. The sensor and relay have been replaced but the fan still doesn't come on automatically. A switch is currently wired into the relay connector to manually turn the fan on when it reaches operating temp.
A few weeks ago, it began dying on her. Most of the time it throws a code #34, but not always. Once it dies, it becomes increasingly difficult to start, and to drive without it dying. It will keep dying quicker and quicker.
Here is what we've done:
- Replaced MAF sensor (twice).
- Replace ECM.
- Replaced coil (the old one was not mounted tightly and was arcing at the mounting point and seemed to have a weak spark even after tightening it).
- Replaced cooling fan relay and temp sensor.
- Fixed loose ground pin at ECM connector (it has several grounds).
- Tightened leaking cold start injector fuel line connector at fuel rail.
- Fixed bad vacuum line at EGR valve.
- Partially cleaned throttle body without fully removing it (it was vey dirty inside)
- Replaced K&N air filters with paper ones.
- Cleaned air temp sensor in front of filters.
- Tested EGR valve (seems to be working, when manually actuated RPMs drop, and vacuum applied to it actuates it).
- Disconnected MAF sensor and RPMs dropped, reconnected and runs better, so it probably works.
- Found a clogged IAC valve (replacement has been ordered), it seemed to be stuck in partially open position and even after cleaning the piston was still stuck.
- Checked voltages at MAF sensor and cooling fan relay and all seems good.
- TPS resistance varies through range of motion so it seems OK.
- Fuel pressure is good even when it dies so fuel deivery is good.
Car idles a little high (may be related to the IAC valve, we'll know when the replacement arrives). It sometimes stumbles without dying. If this is a vacuum issue, then something else besides the stuck open IAC valve must be leaking vacuum after warm-up. Don't know what else to check. We haven't conducted a spray vacuum leak check yet but need to. I'll post more later.

 

Did your guy regasket the engine before installing it? If not, I would replace the intake gaskets. Along with the intake gaskets, the valve cover gaskets would be replaced. Make sure that the PCV valve is tight in the grommet as well as the elbow in the other cover.

You will want to advise him to do a complete and thorough spray for vac leaks. From the brake booster to the charcoal canister. And especially the rubber ends on the plastic idle air bypass pipe running from the intake manifold to the TB (actually, the whole deal... I had mine come unglued where the TB pipe meets the junction tube at the manifold connection).

Did you clean out the IAC bore in the TB when it was cleaned?

When pulling the codes from the ECM using the paper clip method, the radiator fan SHOULD come on. Is it? If not, check the brown and red wires at the relay for power with the key on. If there is power, use a jumper wire and jump the green wire (at the relay) to ground. If the fan runs, there is an issue on the ground wire (this green one is the relay coil ground). Remove the backup fan switch connector and jump IT to the engine block. If the fan runs, the issue is between here and the ECM. If not, it's between here and the relay.

Also have the ignition module tested. Several times. You want the tester to get the module hot. I've had a module test working when cold and fail when hot.

Check the fuel injector resistance, per bank. Should come out to roughly 4 ohms. 6 or more means a shorted injector. 0 means a shorted harness. And test again when the engine is hot.

 

Yes new gaskets were used. PCV may have blown out a loose line at some time previously, there is some gunk in that area back of th eengine, about like the throttle body was, and one end of the PCV elbow pipe was cracked off unevenly at an angle (so it's not a straight cut on the end, now it has to be pushed even further in). But it's all pretty tight now as far as we can see.

The IAC body & bore were cleaned. We haven't done manual diagnostics since I have a code reader, but we'll do that to check the fan (after we hook it back up), and also I believe all the relays should energize, probably simultaneously with the code flashes? Will find out shortly.

If all else fails, we'll get that ignition module tested a few more times. It was heat tested at Autozone but it's possible it wasn't hot enough.

********************************************

Got the new IAC valve in and it's worse, now it won't even idle for 2 minutes and it just dies. This is probably a continuation of the problem, as it has been getting progressively worse. However at first it seemed to recuperate after sitting a while. Now it's constant.

Fuel pressure at the rail remains constant (about 50LBs) after it dies and bleeds off very slowly. Good coil signal to distributor using inline plug wire light (haven't checked individual plug wires yet, need to do that too). The coil signal flickers rapidly during start, and stays on constant when running, and for a second or two after it dies (and it dies abruptly) it goes back to flickering.

This has to be something so simple. We're getting ready to put the computer into diagnostic mode with the fan hooked back up to see if it kicks on, and that the relays are all energized. Then need to run the vacuum leak spray test if we can get it running again. The problem now is getting it started and running. Also I brought my ignition and sensor test kit, it has a plugin circuit tester for the IAC if we can get it running. Also perform the fan and injector checks. Whew.

 

Test the fuel pressure with the engine running. Should be not more than 47 PSI or there is a restriction somewhere between the pressure regulator and the fuel tank. Fuel pressure should NOT lose even 1 PSI of pressure in 20 minutes after the fuel pump has shut off.

The only relays that will be utilized during diagnostic mode are the MAF and fan relays. The fuel pump relay will only be used for 2 seconds when the key is turned on. The IAC should also be setting itself to "home" position, and you can put your fingers on it to check (or it may make a loud clicking noise, especially when you turn the key back off again). You should feel it vibrating.

Code 34 means low air flow detected through MAF sensor OR a loss of signal. Make sure that the valve covers are tight enough (I've found that they need to be tightened more than spec), and that the vacuum hoses aren't deteriorating (shouldn't leave rubber on your hand when touched). The MAF does NOT put out a voltage signal. The V6 MAF is a screwy one. The signal is actually a PWM frequency. If you have the ability to check, the signal should be about 32 Hz at idle.

Set your DMM to measure resistance and check the plug wires. No single wire should be over limit when the meter is set to measure 200 (I believe) ohms max. As for the fuel injectors, each injector should be NO LESS than 11.8 ohms.

Disconnect the battery for a few seconds and then reconnect it. This will set the ECM back to base, and help it to learn the new sensors. Also pull a spark plug and note the color of the cylinder end. It should be tan to gray. White is lean, black is rich, and wet black is an oil control problem.

 

Well, first, what happened tonight. The car is about where it was when it was limped home last night, it won't run for more than a minute or so without dying. Previously when it was limped home after a test drive (which lasted up to 10-15 minutes without dying when we first started working on it) it would kind of reset itself after sitting overnight. But we haven't tried to drive it (to see if it's any different under load) since it was limped home last night and we found the clogged IAC. Could barely get it up the driveway yesterday, it took a lot of starts and a good bit of waiting in between.

Currently it won't start at idle, only WOT (to open the throttle body butterfly valve all the way, it's totally closed at idle, right?). Thought that might be a sign of the IAC not being reset (the installation instructions say it has to get up to operating temp and driven at 40MPH to have the ECM reset it). The new IAC was installed with that pintle nearly at the max 1-1/8" so the port would have been almost closed, and it never started and ran long, so we pulled it and pushed the pintle in to about 1" (instructions say it's OK to do this if it hasn't activated, and that it wouldn't activate until it had been driven at 40MPH) to open up the port. Neither setting helped.

Until the last run yesterday that ended in limping it home, it always started at idle after cooling off. It no longer starts without WOT. What other air management is there beside IAC and throttle body? Only thing I can think of along those lines is a huge vacuum leak that is getting switched in, like with EGR or something. Maybe one of those vacuum switches or valves?

And once it is started, you have to keep the RPMs high or it dies within 20-30 seconds of letting it idle down. I don't know how long it would run at high rev because we haven't kept it revved up for more than a half minute or so.
I don't know if this is a continuation of the previous problem or a new one. It does seem as though the conditions of both starting ease, and runtime, have deteriorated fairly steadily but we didn't document anything like that to be sure. Except we know it hardly runs at all now after limping it home in that same condition last night. So it could be a continuation/deterioration.

We tried the diagnostic mode with fan relay connected and the fuel pump relay is activating but the fan relay is not. Didn't get any further into that. I thought for a time that the two problems were related but the running condition has worsened while the fan problem is constant. I have not checked the continuity of the cooling fan relay wire from the computer. I think the ECM supplies a ground to activate the relay and turn on the fan, right? If so, if memory serves me correct it may be grounded (I think I checked it once, will have to re-check that), but that should make it turn on, right?

I can't remember exactly what I found at the MAF relay and MAF connector before, but I remember it all checked out good. The computer voltage at the MAF connector was good (around 5V I believe) as was the 12V supply from the MAF relay. Pretty sure the MAF itself is OK after three tries to replace it. So I would think the computer is getting the PWM signal (I don't believe my multimeter can detect a waveform or digital signal). But I have not checked continuity of that wire to the ECM.
I am starting to lean toward something with the fuel delivery, either cutting off injection or totally shutting down the air supply all at once. When it dies, it is abrupt, no sputter or anything, it just shuts right down, so that makes me lean toward fuel injection shutting down. And the coil keeps firing for a couple seconds, as long as the engine is still turning. So the computer doesn't know it's dying, it keeps sparking, but there must not be any fuel being delivered, even though fuel pressure still exists at the rail port. I was told the fuel pressure is 50PSI but that might be an approximation, I can't tell you for sure. The fuel pressure does slowly bleed off after shutdown, but the tester is a cheap Harbor Freight deal with a leaking bleeder valve so maybe that's it. Probably need to get a better pressure tester. But with fuel pressure and spark, all that's left is injectors or total cutoff of air supply (is that possible?).

Can one bad injector drag all the other ones down so that they do not function? We still need to do the injector resistance test.

Can't do any testing that requires a warmed-up motor. The problem used to happen after about 10-15 minutes of run time and some driving so I thought maybe it was temperature-related, but now it happens all the time even when cold.

The ECM has been reset a bunch of times, currently has no code. It limped home with a 34 last night but after reset first thing, nothing today triggered a code. And it was dying big time. I almost fear we've introduced another problem. Don't know what it could be though.

We'll pull the intake plenum to see how many injectors we can get at. I have a noid to test the circuit for each one. I have an IAC circuit tester but it needs to be running for that.

 

car shouldnt start at all with the throttle open more then 50% iirc , i dont recall the exact number but if the tps reads higer then a certian throttle opening while cranking the ecm goes into flood clear mode

if the car is starting and running with the throttle that far open u either have the cold start injector leaking or one of the port injectors leaking pretty darn bad

tps voltage should be between .0 and .50 at idle/closed throttle and between 4.50-5.0 volts at wot

 

The cold start injector dumping fuel would make sense, that would almost explain everything. We have thought that it might be getting flooded (some indications but nothing definitive - occasional fuel vapors from the tailpipe when trying to start it, black smoke when it starts). And of course having to WOT it now when starting. We do need to check the plugs.

There just isn't a whole lot of info online about the cold start injector system. I had to do a lot of digging just to find a reference to it other than a parts store. The wiring diagram identifies an injector and switch, there appears to be a unit at the front of the intake manifold, more to the driver's side, and another unit on the center rear of the intake, they both have a connector and a hard fuel line going to one of them (the rear one I think, which is centered on the intake so that would make more sense), so that would probably be the injector and the one up front would be the switch.

Would disconnecting the switch and injector be a good way to test that?

We may have been sidetracked on the MAF #34 code, that was probably just the stuck open & dirty IAC valve. That hasn't happened again so the new valve may have cured the MAF code. Guess we won't know for sure until it gets back to being drivable. But I always suspected we were looking at more than one issue since we didn't always get the #34 code when it died. And I couldn't figure how the MAF could kill the motor, especially since unplugging it only caused an RPM drop and rougher idle.

 

the cs injector switch is located front driver side of the intake right nexto the coolant temp sensor, im not positive on its operation but that switch controls the cs injector

the injector itself is at the back of the intake in the center on the lower portion of the intake manifold the iac hose should run to the back of the intake and down tot he base this has to be hooked up properly or the cs injector wont work properly



deff check the plugs if they are fuel fouled even if u fix the problem the car will run like dirt with the fuel fouled plugs , for the 6-9 bucks for 6 plugs i would just replace them if there is any doubt about there condition


even if the aic was stuck wide open the air passing threw the iac is still metered by the maf sensor so that shouldnt cause a low maf error code

 

First, if the MAF is under or over-reporting the airflow through the intake to the ECM, the ECM will either remove or add fuel accordingly. Same with the CTS, if it makes the ECM think the engine is colder than it is, the ECM will add too much fuel.

Second, the coolant temp unit (by the thermostat housing) with the blue injector connector is the switch for the cold start injector. The thing in the back of the manifold is the injector itself. Try disconnecting either or both and checking the fuel pressure again. It's possible that the CSI switch is shorted and leaving the CSI open. Not sure exactly how it works, since the power side of the circuit cuts off when the starter solenoid is turned off, but, supposedly, the switch holds the CSI open until the coolant temp reaches 100*F.

Third, if you can only get the engine to start with the ECM in Clear Flood mode (shuts off fuel injection), you've probably got a leaking injector or a shorted injector. Yes, since all 3 injectors on the same bank are electrically connected (hence Multi-Port Injection), one injector can mess up the other 2 on the bank.

Which is why I said to pull the spark plugs. You don't know what's going on in the cylinders without pulling out the plugs.

Also, remove the vacuum line, running to the TB from the fuel pressure regulator, and check to see if there is gas in it. If so, the FPR diaphragm is leaking and that is one cause for too much fuel. And double check to make sure the FPR vac line is in the proper hole in the TB vacuum block. One hole is ported vacuum and the other is constant (manifold) vacuum. The FPR needs to be in the manifold vacuum supply.

Only REALLY LARGE vacuum leaks include the brake booster, idle air bypass pipe, PCV system, and the valve covers. But checking the fuel injector o-rings and intake bolt torque wouldn't hurt, either. However, I've found that if you can't take your foot off of the go pedal and have the engine idle until the temp gauge registers that the engine is warming up, it's generally a MAF issue, IF everything else is good (no vac leaks, proper fuel pressure and good fuel injectors). What I would start by doing is to literally unplug EVERYTHING connected to the engine via vacuum lines/hoses and see if the engine wants to run then. If you don't have a vac gauge.

And the TPS should be about .55 VDC at closed throttle.

 

Thanks everyone for assistance so far, you've helped me organize thoughts and concentrate, been sidetracked too many times. Just a couple of backyard mechanics and this stuff can be complex. So we really really appreciate your time and help. You have also helped verify my understanding of much of what I have read, and to throw away some of the misinformation I've also found. You all clearly do know your stuff and I wish I'd joined and posted this issue earlier.

I did realize after my last post that even the IAC air is post-MAF so it's metered air. Back to my first guess that the ECM just thinks the MAF isn't reporting correct air flow since it's not getting correct readings elsewhere, and the MAF code may just be a symptom of the problem at large.

Anyhow, after my last post, I did find some good fuel injector/CSI reference material. The ECM also has a timer circuit that cuts off CSI, along with the temp switch. And I thought the wiring diagram in our manual showed the injectors for each bank tied together, so it makes sense that a whole bank can go bad if shorted.

Keep in mind this engine has been swapped in. Anything can happen in that process.

We don't have a good pressure gauge but I think we can stop the purge valve leak with a hose and plug (we were just blocking the hose with a thumb but it had air in the line. The pressure was bleeding off before and not holding, not sure if that was the bad purge valve or the regulator.

Had to take the day off Saturday, we'll be getting back on it Sunday (24th). The more I think about it, the more it seems like an injector issue. Should have some solid info to post later.

 

Um, no... The CSI and ECM have nothing to do with each other, except that the ECM is calibrated differently than the later ones for starting under 100*F due to the CSI system.

http://92b4crs.tripod.com/86wiring/dia-pics/21-6.jpg

Yes, I know it's for an 86, but the wiring didn't change on the V6 until 89...

If the MAF is giving a code 34, and it's good and has power and signal going to the ECM, then you have unmeasured air entering somewhere along the line.

It almost seems like you've got 2 problems... Too much fuel and too much unmeasured air in the cylinders, and the ECM can't compensate.

Again, the only way to know either one for sure is to pull the spark plugs.

Also, when was the last time a FULL tune-up was done? Has the oxygen sensor been replaced at any point? That may be another thing to replace down the line, but you want to get the engine running decent first.

 

Vacuum all checks good even at the fuel pressure regulator, and I'm told the cruise control works fine with no adverse impact (vacuum-actuated), so I don't think vacuum is an issue. Fuel pressure is close to 50 psi and no bleed-off now that we made sure the gauge isn't leaking. CS injector doesn't leak when wiring plug is disconnected during fuel prime (ignition on but no start), and it does inject/spray continuously during cranking. Some plugs are a little fouled from running rich, some are a little better, none look perfect.

All 6 regular injectors measured about 15.8 ohms (book spec says 11-14) through the two terminals on the injectors. The CS injector measured just 6 ohms (Shouldn't it be the same as all other injectors?) through it (It does operate differently, where it appears to inject continuously during cold start operation). No injectors were shorted to ground on either terminal. Wasn't sure how to read the wiring itself but I took the following readings (with the ECM hooked up) at the connector for one injector on each bank: measured across the two contacts in the connectors and got 3.8 ohms on one bank and 4 ohms on the other; measured from ground to the black wire that goes to all injectors and got about 20 ohms; measured from ground to the pink wire that goes from ECM to one bank of three injectors and got about 15 ohms, same with the green wire that goes from ECM to the other bank of three injectors. All regular injector readings were consistent so I'd say they're normal?

Wiring diagram shows the cold start system works directly from a 3A fused 12V supply that either runs through the injector to ground through the thermostatic CS switch during cold start operation, or when the CS thermostatic switch hits operating temperature (someone said 100 degrees F?), it opens up that circuit and the alternate circuit is used. The switch had one terminal completely shorted to ground (cold start circuit) even though the diagram shows it should have had some resistance to ground, and the other had about 32 ohms to ground (alternate run circuit that bypasses the CSI when the CS circuit opens up at temp).

Oh, and our wiring diagram shows the CS power supply remains on through test (lights), start, and run. It just switches to a different path to ground than the CS injector after the switch reaches its operating temp.

We pulled the CS thermostatic switch and hit it with a short burst from a propane torch, and the shorted circuit increased resistance to about 135 ohms to ground and stayed there even after it cooled down. According to all wiring diagrams I've seen, it should have gone open. The alternate circuit went from about 32 ohms to ground, up to 65 ohms to ground. Both of those hot readings remained even after it cooled down (and I ran it under warm and then cool water for a long time to cool it off). So I think the CS switch is bad and was keeping the CSI injecting (maybe not completely, but some) even after warmup, when the ECM begins managing the fuel/air mixture. But I don't understand why the switch resistance readings didn't revert after cooldown.

Also found one loose spark plug that was allowing some blow-by, don't know how much of a factor that would be, but possibly significant? It was about 1/2-3/4 turn loose, definitely had some combustion deposit up one side of it.

Also removed the throttle body and totally cleaned it out, the back of the butterfly plate was definitely fouled up and coated with black soot.

So we are down to getting another CS switch and putting everything back together to test it.

 

Posting up exact numbers would help...

If the fuel pressure is above 47 PSI, it's too high.

Vacuum should be around 16-17" . And the needle should be steady.

Do a compression test as well to cover all the bases.

Pull a plug and crank the engine (unplug either the front fuel injector harness connector or the 4-wire connector at the distributor to shut off the fuel injectors). The spark should be bright white. If not, there are other issues.

Ok, for the CSI...

1. It ONLY works when cranking. It can't get power if not.
2. There are 2 wires to the switch. One will always have resistance if the switch is good because this is the heating element (purple wire). The other will be open or closed based on how hot the switch is, either by the heater or by coolant. If the switch remained around 100* after you hit it with the torch, it may have still been open.
3. Finding either the injector or switch is like looking for parts for a 2000 Yugo...

 

We don't have any exact numbers. But I will try to get some. We only have short time frames in the evening to work on it and so we're just busy verifying the operation of main systems.


On the CSI, the Haynes manual shows the CSI circuit hot through bulb test, start, AND RUN. It would make more sense for it to only have juice during start. And those books have been wrong before. But the resistance of both circuits through the CS switch just increased, and the switch circuit didn't open as it should have. And we got it pretty hot (well above 100F).


Like I said, I cooled the CS switch down. Way down. It was under very cold running water for several minutes. We'll check it again today to see if it reset.


We have noticed a possible weak spark before just visually inspecting, not scientifically. It's why a new coil was put in it. I guess we haven't verified the full output of the distributor. But I have a spark tester and will check that tonight also. Most of our time last night was disassembling the intake and throttle body and cleaning them and pulling plugs and testing injectors.

Are there two possible thermostats for this engine? My buddy says he put another one in when it first overheated, and was given the option for a 150-degree thermostat and put it in. To me that sounds like it might run cold in winter, which might mess up the computer.

 

3 thermostats... 195 is stock, 180, 160... Don't touch the 160 if the girl values gas mileage (won't go into closed loop).

I've said it before and I'll say it again. Haynes is a $15 firestarter. That's all it's good for. They also show a knock sensor for the 2.8. No RWD 2.8 EVER had a knock sensor.

 

The CS switch reverted to normal (original) readings after cooling of overnight so it's back in the car.

Gave the throttle body & blade a good cleaning, and it really needed it on the backside. Especially one very thin port right down where the blade seals against it.

That loose plug (#5) was loose enough to get significant combustion deposits up along most of the metal body. I believe it was the cause of the intermittent MAF sensor code, as it would have also pulled in un-metered air during the intake stroke. Had to be affecting vacuum (still haven't taken an official vacuum reading). All new plugs in the vehicle now.

We put it back together and got it timed exactly right (it was off before, the correct procedure wasn't used to time it). And probably because of the loose plug the idle was previously set artificially high with some tape acting as a spacer on the linkage stop to keep it from dying at idle (I'm just finding some of this out and putting two and two together). With timing set right and tape removed, it starts and idles and runs great right now, better than before, and hasn't stumbled or died during a couple of test runs. Need some more test runs but I think it may be resolved, IF: if the computer was compensating for the excess unmetered air and adjusting fuel flow to its adjustment limit without realizing the expected improvements, and those adjustments either caused the car to shut down or the computer entered some kind of shut-down mode without throwing a code. Does it have such a thing, a fail-safe shutdown if it reaches the limits of its air-fuel adjustments? It must have adjusted air/fuel to compensate without seeing expected improvements, so the thing is, how does it react at that point? Just continue trying to run at the limits? Or shut down?

 

There is no fail-safe shutdown mode. The later ECMs actually have anti-stall programming. The ECM will try to keep the engine running at all costs if it possibly can.

An example is that the ECM has no ties to things like the oil pressure unit... Even if the oil is gone out of the oil pan, the ECM will continue to run the engine until it locks up and can't run any more.

 

I thought the oil pressure switch will cut off the fuel pump (especially for situations like rollover)?

Bad news - it died on the third test run. No code, just died abruptly. It will restart fairly quickly by turning it over a few times without touching the gas pedal (this step may or may not be necessary, but as it works we continued doing it this way until we got it home), and then stepping all the way on the pedal for WOT and cranking it, it turns a few times and catches. So it must be flooded. But it will only run for a short time before it just dies again. When it dies, it can occasionally be saved by shifting to neutral and feathering the pedal, but it will run rough until it dies again, which is usually fairly quckly. Once it dies, it wants to stay dead. It must be something that occurs after it warms up. I've followed it every time we test drive it, and all I can see are wisps of fuel vapor coming out the tailpipe as it dies.

We re-checked the error codes every time it died, and it eventually threw the #34 MAF code again. That's clearly just a symptom of the problem and not the cause. It never throws another code (well, except for when we disconnected the spark control line when we timed it), and only throws #34 after it dies a few times.

The computer would throw a an O2 sensor code if it's misbehaving in any way, right? I'm trying to come up with an explanation for why it only does this after it's warmed up.

So far we've fixed a loose ignition coil mount, a minor vacuum leak on the EGR valve, a loose spark plug, a fuel leak at the CSI connector, and replaced a clogged IAC valve.

On a side note, I found that the new cooling fan relay is bad, I did a functional test on it. We're keeping the manual relay bypass switch in place until it's replaced.

 

1. The oil pressure switch is a backup to the fuel pump relay, period. Again, the ECM does not know nor care how much oil pressure the engine has, and will run the engine regardless of how much oil/good oil is circulating in the engine. Case in point? Lot of cam failures on early 3100 engines due to faulty intake gaskets leaking coolant into the oil, which thins out the oil until the cam loses lubrication enough that it locks up and snaps (hollow cams on later cars).
2. Fuel pressure test... It's been said several times now. Need to make sure that the CSI isn't sticking open with the engine hot. And to make sure it's not above 47 PSI. Also pull the vacuum line out of the TB block for the pressure regulator and make sure there isn't any leaking fuel with the engine hot (if you're going to do this with the engine running, you will need to put a finger over the TB port or the engine may possibly stall due to vac leak).
3. O2S is completely ignored by the ECM until such a point that the coolant temp (as reported by the sensor) is 160*F and the O2S itself reaches 600*F and produces a useable voltage signal (aka Closed Loop operation). Which is why the code 44 or 45 takes forever to show up. Code 13 usually pops up early because the O2S is disconnected from the ECM in one way or another. And may also be another code...
4. What's the resistance of the other coolant temp unit (the round one, the actual CTS)? Cold? Hot? And test the fuel injectors the same... Just unplug the 4-wire connector and probe between A and C and B and D to get the resistance of the injectors per bank.
5. Also check to make sure you have spark when the engine fails hot. Electrical problems tend to get worse the hotter they get. Carry a spare plug and just unplug one of the plugs to check (don't remove a hot plug!).
6. Manifold vacuum reading? Vac leak check (don't forget the bellows connecting the MAF to the throttle body! I had mine split at the valve cover tube connection!)?

 

Thanks! Good info, will try to get into as much of that as possible tonight (took a couple days off).
I just ordered & received Hatch's Computerized Engine Controls textbook and have done some reading.
1) On the oil pressure, I thought the pressure switch would cut off the fuel pump relay (independent of the ECM) if pressure drops to zero, since it does this on other vehicles I have encountered (supposed to kill the engine in case of rollover). But the textbook gives the same description you do, of providing fuel pump relay backup. And if I remember correctly, the wiring diagram does show that it's hooked up to the relay power in parallel, not serially.
2) Not sure how we'll test the CSI with a hot motor. We know it's operating properly when cold (sprays and stops with crank/no crank), and between it not getting the spray pulse except during crank (verified), and the thermal time switch keeping it from spraying after it warms up, and the fact that it begins the dying problem before we ever try to re-start it when warm, I seriously doubt it would be sticking open.
- On the CSI, it injects into a small manifold port (very narrow in the physical drawing) that is open to both sides of the plenum. That manifold port is also connected to the PCV valve, and the throttle body's IAC valve port. I have an idea that the soot from the PCV valve in a worn motor might be clogging up the manifold port, causing it to back-pressure into the throttle body and clog up the IAC valve as well as sooting up the backside of the throttle blade (while the book does say unburnt fuel vapors from hot shutoffs cause buildup on the backside of the blade, the buildup I've seen on the IAC valve and the backside of the throttle blade is way too sooty to be caused by fuel vapors and shouldn't be caused by atmospheric impurities in filtered air). And I know there is a similar port in the intake of some Ford motors that performs a similar function, and throws a trouble code when it's clogged, and that it can be blown out with pressurized air. I think I'll try that on this motor just to see if it helps anything (I know it won't cure anything, but it just might help).
4) I haven't tested the coolant temp sensor yet, but it was recently replaced. I know the ECM uses that input for air/fuel management as well as the cooling fan operation. There is another sensor just for the gauge I believe. But I did test every wire in the cooling fan circuit, including the ones to the sensor, and all wires are good, not grounded, and appropriate voltages are present during appropriate times. Since the ECM was replaced, I'm assuming it does send a ground to the relay, although we haven't gotten it hot enough to test that (it keeps dying lol). And I did verify the relay is bad by energizing it and testing continuity through the two used circuit contacts. The off relay contact (unused) has the expected continuity from the 12V fan supply contact when de-energized, and those two contacts go open when energized. But the other two contacts used to supply that voltage to the fan do not close when energized.
5) We had an inline spark tester on the coil-to-distributor wire and it kept sparking as long as the motor was turning after it died. I'm assuming a visible spark passing from coil to distributor also means it's passing through the distributor and grounding through the plug. We haven't gotten the engine to full operating temp but a couple of times, it usually fails before that (though after a warm-up period of several minutes).
6) Earlier on, I pulled a couple vacuum lines and smelled them and they smelled faintly of fuel. Normal?
Once again, I will try to get exact readings and post them. Every time we run into something we think may be the problem and work on that and forget to get the readings. It's on the list.
*Here is where I'm at now: This is starting to look more and more like a fuel cut-off problem. I know there should always be air, reading the Hatch book I find the ECM will always try to at least maintain an idle speed by opening the IAC if it starts to die. And I'm certain we are getting spark even beyond failure, and I know we have fuel pressure beyond failure. The only uncertainty has been if the injectors are pulsing at and beyond failure. And I found some info in the Hatch book that makes me think we are losing spark.
First, the TPS can be misadjusted or malfunction (usually with a bad ground) and fool the motor into thinking it's at WOT when it's not, triggering Flood Clear Mode which shuts off the injectors in the 2.8L. My test on the TPS so far has been to verify a corresponding linear increase/decrease in resistance through the two sets of contacts as the TPS lever is moved through its range. Since that has been consistent I haven't bothered to check for voltage levels. But I need to check the voltage going into and out of the TPS, and verify a good ground. This can interfere with restarting, and perhaps explain why it will only start at WOT after it dies.
Second, I found in the Hatch book a description of something called 'fuel cutoff mode' which happens not only when the ignition is turned off, but also when the distributor reference pulse (DRP) stops coming to the ECM. And if the ECM doesn't see the DRP within 2 seconds of cranking, it shuts off the fuel pump by de-energizing the relay. So a bad DRP signal could cause both the dying and the hard to restart problem. We need to keep a fuel pressure gauge hooked up next time we drive it and see if we're getting fuel pressure on restart attempts (I know, I said I was able to restart it by cranking without touching the accelerator for a couple seconds, then turning it off and trying again with WOT throttle (which has worked the few times it was tried and we didn't vary the pattern) and while that doesn't seem to fit the fuel cutoff pattern it's possible that the DRP is coming back on the second try?). It could also be a combined problem of DRP and TPS. The Ignition Control Module has been run at the local Autozone, but perhaps if the DRP wiring checks out good, the module should be re-tested. I'm told they may not have run it through the full test of several cycles to make sure it's properly heated up.

 

1. The fuel pump relay and the oil pressure switch have the same power feed from the same fuse (which is the same fuse as the ECM constant power... Bolted to the frame rail on the passenger's side behind the headlights), and send power to the fuel pump via the same wire, the tan/white. The OPS does NOT control the relay's power supply and does NOT interrupt the power flow to the fuel pump if either a. the engine loses oil pressure or b. the switch/sender fail. Yes, there is a fuel cutoff mode. The ECM shuts off. So does the power to the fuel injectors. No power to the ECM=no ground pulse to the injectors, and no power speaks for itself. But that won't shut off the fuel pump until the oil pressure switch opens with the oil pressure below 15 PSI. Which means fuel is being delivered to the rail but not injected into the intake.
2. To check to make sure the CSI isn't sticking open with the engine hot, all you need to do is to check the fuel pressure and make sure it doesn't drop with the engine off. However, you have yet to figure out if there are any problems with either the FPR, fuel hoses/lines, or leaking injectors, so this may throw you off.
3. To test the radiator fan, all you need to do is use the paperclip method to pull the codes. If the IAC isn't moving (put a hand on it to feel for vibrations) or the coolant fan doesn't run, there is a problem.
4. Reset the TPS to .55 VDC between the gray and black wires, and then make sure that there is no dropout between closed throttle and WOT. Almost would say it's better to use an older DMM with a needle to check for voltage signal dropout.
5. You have the idle airflow backwards. The idle air goes up through the throttle body (if you look at the front of the TB, there is a slit to the left of the throttle plate which is the IAC bypass passage), around the IAC pintle, through the air tube, and into the manifold. The PCV stuff gets sucked straight into the lower manifold, does not go anywhere near the IAC. What you see as soot is actually the EGR flow.

Best to get a nice long hose on a fuel pressure gauge and go for a drive until the engine dies. If the engine is indeed being starved for fuel, the pressure test will show that. Since you have hot spark, fuel is about the only thing left other than an electrical issue outside of the ignition.

:edit: How old is the catalytic converter/muffler? May be plugged. It takes a bit of time for the exhaust to backflow into the engine enough that the cylinders can't get enough fuel/air mix into them to fire. And then it takes a bit of time for the cylinders to vent enough (however they do it) to fire again. Which could explain the code 34 (can't draw air into the cylinders if you can't push it out again!). Easiest way to test, which WILL throw a code (BTW), is to remove the oxygen sensor and take the car for a drive. If the driveability improves, the cat or muffler are plugged. Try this before taking anything else apart. It's possible that the exhaust gases got so hot that the guts of the converter melted.

 

OK, on #1 I was actually agreeing with you, I previously thought the OPS energized the fuel pump relay, as the Haynes wiring diagram shows the OPS switch in line with the relay and pump, but this wiring diagram (which is a more logical diagram) shows the OPS actually providing power directly to the pump in parallel with the relay, so when I mentioned that I was acknowledging my previous mistake. http://ww2.justanswer.com/uploads/2p...640_engine.pdf
On #2, the fuel pressure was not dropping when we had a good gauge hooked up to it during and after it died while idling (after idling several minutes).
On #3, I verified the cooling fan relay is bad by actuating it and testing continuity through the two contacts for feeding the fan. Everything else checked out good. So we need a new relay.
On #4, I loosed the mounting bolts on the TPS and moved it around and got corresponding rise and drop in idle speed (which was quickly adjusted for by the ECM). It's just set back in the middle mount position, where you would naturally expect it now.
On #5, according to the IAC diagram in the Hatch book, that same vacuum port (which is not primary vacuum used to actuate anything) that the PCV valve goes to, is the same opening in the manifold that the CSI sprays into. And it tees off to the back side of the IAC valve. Which made me wonder if the PCV feed eventually clogged up that very thin-looking port in the manifold (as I've known it to do in Ford Windstar V-6 motors). Would the vacuum produced at the other end at the IAC valve where it opens to the intake air flow, cause it to suck the PCV's venting into the throttle body? It's not important, I was just speculating. Ford has a shop fix where they blow compressed air into those intake ports to clear them, does GM do the same thing? Or is the hatch diagram incorrect (it's specifically for the 2.8L)?
*The catalytic converter is new. I believe the original motor overheated pretty bad when the cooling fan stopped working in summer. The replacement motor has a lot of new parts from when it was installed a year or so ago.

OK, now for the new update - because of what I found about the ECM entering fuel cutoff mode if the distributor REF pulse is lost (which would hypothetically cause exactly what we've been seeing), and the fact that it's the same distributor from when it overheated really bad and cooked the lifters and rings, we pulled the distributor and took it apart. The pickup coil looked like it had been overheated, the wire insulation was brittle and cracked in several places, including right where it bent to run along the channels underneath it in the distributor body. I did a little checking and found that not only was the part easily available (which tells me it might have a known failure issue), but the symptoms listed for a bad one matched exactly with what we were seeing. So, it has been replaced and the first test run went fantastic, but we have a couple more runs to go before we can call it fixed. But there just isn't anything else that makes sense, the way it just up and dies without a whimper and often without throwing any codes at all. We've verified that fuel pressure remains after it dies, and according to what I've read the ECM will maintain IAC air feed to at least keep it idling if RPMs drop below 600 or so, and fuel injectors being cut off are about the only thing we are left with. It runs fine until it dies, and it dies so abruptly, without a backfire or a sputter or anything, and usually without throwing any codes. I just can't believe something as crucial as the REF pulse existence, that was significant enough to merit a section in the Hatch book, does not have a corresponding trouble code (at least I couldn't find one for it) if it fails. If that is the problem (and what else could it be?). So, over the next few days we'll test drive it a couple more times and see if it's fixed. It certainly runs better than before, with all the fixes we've done along the way.

 

Um, code 12 literally means "ECM not receiving DRPs". (DRP is Distributor Reference Pulse)

Replace the entire distributor. If the engine got hot enough to screw up the pole piece and the PU coil, then the pole piece may be damaged. No, a reman dizzy isn't cheap, but you won't have to deal with the damage-prone GM parts (except the ignition module).

 

Car's been sitting a while. Finally got another test run tonight, it died. Haven't checked the code but if it has one it's probably the MAF code again, which seems to be secondary to whatever the real problem is as it doesn't always come up when it dies.

On the DRP code 12, that is the code that it blinks when you pull the codes manually. And it does it because the key is on and the engine isn't turning. So I don't know if the scanner knows how to tell, or if the computer even has a way of differentiating, between a stored 12 code and a 12 code that's present simply because the key is on and the engine isn't turning. Or if the scanner just ignores the 12 code. Or what. The 12 code doesn't appear in the list when there are other codes, so perhaps that means it's not a stored code?

Anyhow, we're back to square one.

 

Again, for the code 12, see above. It's not a symptom but a result of one. The ECM doesn't "store" this code. It's only when code 12 is NOT displayed when pulling codes that you need to worry about it (engine isn't running, usually, when pulling codes).

When the ECM stops receiving DRPs, then it shuts off the fuel injection and the engine shuts off. If you can, hook up the scanner while going on a test drive. If the RPM signal drops out while the engine is running, the engine will stop.

In which case, you would need to check the wiring going to the ignition coil and between the coil and the ignition module first (I've noticed that the small wires at the 2-wire module connector like to just about break). If those haven't been melted or otherwise damaged, then a replacement distributor is in order. The replacement will come with a module, which would be another thing on the list.

 

I'm looking for the timing degrees settings for my 2.8L v6 MPFI 89 Pontiac Firebird.

 

Well, just a week short of two months, had to get some other vehicles out of the way.

Maverick H1L - the last thing we did was remove the distributor and inspect it real good, the pickup coil wires looked cracked so we replaced it (the car had been overheated before and the whole engine was replaced with a low-miler from a junkyard, distributor was one of several components that were kept) but it didn't help. However, I think we are losing spark, and here's why I think that: when it dies, if I floor the accelerator it will fire right back up, though rough, but it runs. It just doesn't run very long before it quits again. So, I know that flooring it while starting puts the computer in Flood Clear mode, with only about 10% injector pulse or something like that, and with the accelerator floored that throttle body butterfly blade is wide open so it's getting max air and very little fuel, and it fires. That can only mean it was flooded and it's starting on the excess gas left from when it died. This can't be an air issue because the air bypass should be working fine (unless the air bypass passages in the back side of the intake are plugged, but we haven't pulled the intake yet so that's an unknown, the air bypass and PCV are all connected to the vacuum port on the back side of the intake I believe), and we just replaced the air bypass valve and cleaned the throttle body out pretty good. Anyhow, it wouldn't just shut down dead like that if it was a rich condition. It's shutting down almost like the key is turned off, you can goose the pedal a couple times and try to keep it running but it goes down quick, and if you do nothing it just dies immediately.

So, I also know that the MPFI fires all 3 injectors in each bank at the same time, and the fuel just sits on top of the intake valves until they open (which must be only in the microseconds of wait time). Put all this together, and it sounds like we're losing spark. We had some possibly conflicting info last time we looked into the spark, we had a loosely-mounted coil pack which was arcing and we tightened it (the coil had already been replaced), and the ignition module was supposedly stress tested properly at the local Auto Zone (although I'm unsure of that because the first time I was told it was only run a couple times and now I'm told it was run a bunch of times), and I had a visual spark tester on the coil-to-distributor line once when it died and the spark kept going as long as the engine was still rolling over. So it must be something in the distributor or ignition module, and we need to do those checks again from scratch.

My scan tool is an AutoXRay Code scout and it doesn't read real-time data, only scans for codes. I know some of that data is present on the OBD connector pins, but haven't tried reading it yet. Perhaps just a test light on it so see if it flickers. One of the pins is for the rpm, right?

 

Um, the tach and DRP signals don't go anywhere near the ALDL. Tach signal goes to the instrument cluster and the DRP signal to the ECM.

Next time the engine shuts off, disconnect an injector IMMEDIATELY and probe the non-pink wire with a test light connected to a battery feed. Crank over the engine and the test light should flash. If not, the ECM isn't getting any reference pulses and therefore, won't fire the injectors. And, since you've already checked each and every part in the distributor (I would have stood there at AZ and watched them test the ignition module until it was good and hot as I have had one that failed miserably when hot), the wiring needs to be checked out.

Or, connect the test light to a ground and probe the pink injector wires to make sure you're not getting a power loss when the wiring is hot.

 

But wouldn't the fact that it started in flood clear mode indicate it was getting fuel when it shut down?

 

It may have been getting fuel when it shut down, but it may not have been from the right place (the injectors).

Is the fuel pressure holding for 20 minutes after the fuel pump shuts off? Does the oil or the intake smell like gas?

Have you done the spray vacuum leak test yet?

Which coolant temp sensor was replaced? The 2.8 has THREE of them (one for ECM, one for radiator fan, one for dash light/gauge) if you don't count the switch for the cold start injector (the one with the injector-like connector).

Pull the spark plugs. From the symptoms, they will either be white or black. Black means too much fuel or weak spark, and white means not enough fuel. If they're wet, it will either be oil (either bad valve cover gaskets dripping oil into the bores that gets on the plugs as removed) or gas (leaking fuel from something attached to the fuel rail be it FPR, CSI, or injectors OR weak/no spark).

 

I thought I would drop a quick line to close down this issue. I thought we had a wiring problem related to the original engine swap and I recommended we pull the intake to examine the injector wiring. My buddy didn't want to go that deep back into it though, so he sent it off to a local electrical shop where they tracked down a couple minor issues and one major one - the injector wiring was incorrectly routed and laying on the exhaust manifold and had melted and shorted out. Thanks again for all the help, color this one done!