Ok guys... HELP! Just bought my son a 91 coupe (he wanted my vert and I said no way!) Its a 3.1L with a 5 speed. Car was not running when I got it because last guy (mechanic he says) had all the wiring screwed up...anyway got all that fixed. Car runs well and will run for 15 min in the driveway but once it heats up it surges,stalls,sputters, etc. Alsomost acts like it is running on 3 cylinders. Snap on scanner gives me code 33. I change Map sensor and connector (tab was broken) I disconnect battery to clear codes, car runs great for 15 minutes and then the surging,stalling comes back. Fuel filter has been changed, oil is fresh, etc.. Any ideas where to start checking will be helpful.

Ok update, I got home from work and the car started right up no issues. I hooked a fuel pressure guage and 40PSi to start and then a constant 38psi for 15 minutes while running. Snap on scanner shows engine temp 100 deg Celsius (gaue in dash not reading correctly) and all sensors operating properly O2 vairable voltage and switching from rich/lean.. car stays in open loop. When i step on the throttle and rev engine to WOT engine dies and will not restart..... Fuel pressure remains good with no drop. Ideas????

First off, the 90-92 models need to be driven in a city-like setting for about half an hour so the ECM can relearn the proper idle settings (known as an idle relearn). Second, are you ABSOLUTELY sure that the coolant temp sensor is giving the proper reading (test at ambient temp with the engine not having been run and cold)? Third, do you have a way to find out if one of the EGR valve pintles (there are 3 different ones of varying sizes) is sticking open?

And last, any new codes?

:edit: Also, remove all six plugs and put them in order somewhere. What color are they? They should be a tan color and not worn down to stubs on the electrodes. Connect them back up, leaving one out, and tell what color the spark is when cranking (assuming you get a spark). There is also a funky ECM problem I myself have experienced, having to do with overheating the ECM itself, but we'll leave that until last.

BTW, I believe that one of the first things ANYONE should do with an older car is a tune up...

Worried about driving it because of the issues I am having. I replaced the coolant temp sensor yesterday and ran the car and now goes into open loop. Car ran about 20 minutes with no issues then threw code 13 but ran good, about 5 minutes later car went back into open loop and the stumble and running rough began and then finally quit running and would not restart. How should I check the EGR pintles? havent pulled plugs yet, but car runs great for 15 or 20 minutes so plugs,wires should be ok.

Thanks for your help, what should I do next?

Well, let me just say this: When I bought my car, I was told by the PO that the engine had just been rebuilt 10K prior. When the knocking and other problems started, I removed the intake and found all sorts of crap under the intake manifold that SHOULD NOT have been there if the engine had been properly taken care of since the rebuild, if it ever happened at all (which I assume it didn't because it had the classic SBC problem of blue smoke on startup and the RMS was leaking). I was also told the T-tops didn't leak, which they STILL do.
The lesson here is: DON'T ASSUME ANYTHING. Just because the car runs at all doesn't mean that the parts are good.

I would first start with a tune-up. Plugs, wires, all fluids (except possibly trans fluid unless it's OBVIOUSLY old), all filters, PCV valve, clean IAC and throttle body along with as much of the intake as possible. But, I would still note the color of the spark plug tips as they are removed. The color of the plugs is a good indicator as to how the engine is running per cylinder.

You have to remove and disassemble the EGR valve to clean it. I don't remember if special Torx bits are required (Torx security/non-tampering bits) or not. Or, you can just start the engine and hook up a power source between the outer 3 terminals (power wires) and the center one (ground). If the engine dies when you apply power to any 1 of the 3 ports, the valve is clear and working.

Code 13 means you have an oxygen sensor problem. Probably either disconnected or the wire is melted to the exhaust (open circuit, no signal is getting to the ECM).

Ok here is the latest, replaced the O2 Sensor (used a Bosch unit) according to Scanner, car goes into closed loop now, runs well. Here is what is new: Wires,plugs,oil change,coolant. Coolant temp sensor,MAP sensor, O2 Sensor, Air filter, Fuel Filter, vacuum hoses,PCV valve, after about 10 minutes of running, gets to 109 degrees Celsius and fan kicks on, etc. Fuel Pressure is 40PSI, after that car goes back into open loop and runs very rough, idles erratic, chugs, cuts out it seems like its running on 3 cylinder, car stalls and will not restart....grounds on engine block are tight.. so can you help me with what are the next few things to check?

What did your old plugs look like?

BTW, most ignition problems crop up or get worse when the system is hot because resistances in the system go up as they heat up. The plugs are the best indicator to this.

Would bad plugs cause the ecm to go back into open loop? Maybe the ecm is bad? How can I check that?

Ok, took the ECM out and checked the plugs and pins, all seem ok, no corosion. Ran car again for 15 minutes and it dies yet again, Check Fuel pressure again 40 PSI to start and 38 PSI even when car is hesitating,stumbling and when it dies. After it dies it will not restart, I check spark and it has spark when cranking. So we have spark and fuel but no start. TPS voltage is good. I have noticed when the car starts running bad i get code 33, but the MAP is new (changed 3 days ago) and i also put a new connector on it. This is driving me crazy! Help!!

When you next get a chance to work on the car, here's what I think is next:

Take the ECM out of its mount behind the dash and let it hang down onto the floor. Run the engine until it dies again. Disconnect the ECM for 5 minutes. Reconnect and try to start the car again. If it runs, you probably have the same problem I did in that the ECM overheats and shorts out internally, killing the fuel supply to the cylinders.

If the ECM fails, call around and try to find a shop that will test it. My local AutoZone fed me a line of and told me they couldn't test it even though they had the test apparatus and the associated cabling (I had b

Well my FP guage on the fuel rail indicates pressure in the system. still 38psi.

ok latest update, ran car till it died and unplugged computer and left it out for 10 minutes. Plugged ar back in and still no start. Scanner says no vats issue, but this time when it stumbled and stalled, no code was thrown. Also noticed MAP voltage of 4.94 right when it died. This is driving me crazy!!!! HELP!

While hot check the resistance of the injectors. Anything under 12 ohms is bad. If they are still the stock Multec units, odds are you need another set of injectors.

RBob.

Do you have a noid light to test for a signal to the injectors? If not, you'll need to get one from somewhere.

According to my FSM (for the 2.8 system but pretty much the same for the 91 730 with the exception of some connectors and pins), you're stuck between an injector problem or injector signal problem, an ECM problem, a bad ignition module, and a stuck EGR pintle. Once you get the noid light, we can narrow it down further.

yes, I have the noid light set, but how should I check the resistance? Also what if I disconnect the egr valve will that help eliminate the problem?

To check the injector resistance: pull the plenum, disconnect the connectors on the injectors, measure the ohms between the prongs on the injectors with a DVM. Can also heat up the injectors with a hair drier.

By this time just about all Multec injectors are or are in the stages of going bad. GM started to use them in our f-bodys in '89. There are tons of threads here on multiple forums with the same symptoms and the same fix.

The insulation on the injector windings (the solenoid portion) breaks down and shorts out. It gets to the point where the ECM can't drive that much current through the injector(s) resulting in having none of them open.

EGR: you can disconnect the electrical connector. But that will not have any affect if a pintle is stuck partly open. What you can do is to disconnect the feed tube at the intake manifold neck and place a piece of sheet metal between the manifold and feed tube flange. Then bolt it back together.

This will ensure that no EGR gases will pass into the plenum. Once everything is figured out will need to remove the piece of sheet metal.

RBob.

Ok, checked for Vacuum leak, right above where the EGR pipe goes into the plenum, there is a strange cut out and there is a vacuum leak there.. Here is a pic.. is this supposed to be there??

Umm, you have a BIG problem there. The question is, why didn't you notice that in the first place, and how does the engine run long enough to enter closed loop when it should be stalling right off? Either way, when you go to test the injectors, take it to a welding shop and see if there isn't anything they can do about closing that thing. If not, you'll need to go junkyard hunting for another plenum. I don't know if some JB weld or similar would stick.

WTF! How does that happen? Well that is a big problem....id say either try and get it fixed like said above or just go to a pick and pull yard and grab a new upper intake plenum. Either way i still want to know how that possibly gets there. Even more that looks intentional; so why would that be done?! At least you figured out your problem tho man. Good luck

I closed that up, I also pulled the plugs they are tan in color and look ok, but the gap is .055 so ill change them. What is driving me crazy is according to my scanner after about 15 minutes running, something is causing the computer to go back to open loop, then to colsed then to open then to closed, then finally open. Thats when it starts running crappy. I am trying to figure out what in the world that could be.

I'd get that hole taken care of before I went any further. I think that the problem is that the ECM doesn't know whether to believe the MAP sensor reading or not, and that's why the code keeps popping up. See if you can't find something to stick in that hole temporarily and see what happens. Just make sure that whatever it is can't get sucked into the intake .

Yes, that WAS intentional. Why, I don't know, but that was made with a grinding bit of some sort (you can see the marks on the edge of the hole).

Also, these engines run best on stock base AC/Delco R43TSK plugs. I know that in this time you're probably tempted just to go for AutoLites because of the price, but they're junk. I've used them temporarily before (when an idiot at school recommended I change my NEW plugs) and was sorry I did. I had them on for a grand total of about a week... JUNK.

Ok, I had the Ignition Module tested at AutoZone, they said it tested good. I also purchased the ac delco plugs as you suggest above and will put them in along with the new wires. So cap,rotor,plugs and wires are all new. I did notice one thing though while reading more threads... i tried spraying starting fluid into the plenum after it started running crappy and died.. The car did attempt to run again. Maybe I have an injector pulse problem? ECM? Bad ground????
What should I check next?
Thank you for the help

The resistance of the injectors, or make it easy and just replace them.

RBob.

In my GM service manual it says in order to test if the ECM is seeing the reference signal and controlling the injectors, you can use the 4 way injector connector by using a test light between terminals B & F and A & E and if the test light blinks while cranking the ECM should be considered ok. Well There is a plug at the top of the engine right behind the AC compressor with 6 wires, that looks like it leads to the injectors. So I unplugged it and not knowing where the B and F or A and E terminals are I tested all of them and get a steady light which directs me to another part of the flo chart to test the resistance across those. Im not sure where the connector is and where those specific terminals are. I cant find a diagram.

Help!

If you were to clean the connector a little bit, you would see on it that each terminal is labeled. LMK if you can't see the labelling... I'll dig mine out and let you know.

You should be disconnecting each injector when the engine is hot and stalling so you can test them. Hook the noid light to the connector when you do so and crank the engine to see if you have a signal.

If that is the correct connector (behind the a/c compressor) I cant see the terminal labeled, can you send me a diagram please

Latest Update, after changing cap,rotor,wires and plugs, the car still dies and will not restart after running for 15 minutes. But while getting to engine temp and you give it gas to check the TPS voltage from idle to WOT it will stall on the way back down the rpm range. But if the car is cold, it will restart and idle fine.. Help!

Replace the ignition module even if it did test good. I've had a couple test good and relaced them anyway and the car would run fine afterwards. If it still persists, continue looking into the fuel injectors.

Yours is probably behind the A/C compressor. I deleted my A/C compressor a few months back so my connector is next to the thermostat housing instead (or would be if I had my 91 harness installed, which I don't at the moment). When I get back from work, I'll see if I can't help a little there... I don't have a connector pinout diagram for that connector as I don't have a 91 FSM, only wiring diagrams for the major front end components.

Oh, and I agree with the guy above... With as many modules as my car has eaten in six years (3 so far), and without knowing how old yours is, I would recommend biting the bullet and getting one. Personally, I myself and a couple of other guys keep a spare in the car because nobody knows when the frigging thing is going to crap out and leave you stranded .

Okay, now that my internet is back running, I can post.

With the locking tab on the top of the injector harness, the terminals from left to right are: Top, F E D, Bottom, A B C. The C and D terminals are for the CTS, the other four for the injectors. A and E are for the passenger's bank and B and F are for the driver's bank.

Ok, I changed the module and still have the same problem. Here is an interesting point though, while checking my TPS voltage with my snap on scanner and revving the throttle, then engine seems to stall and not restart even when engine not to temperature. Ill check the resistance in the injector harness next, what should the reading be?

Each bank should be around 4 ohms. When I say around, I mean within half an ohm... 6 ohms means a bad injector. Each injector should be around 12.6 ohms... Someone might say different, but that's what I usually get, and GM spec says "more than 8 ohms".

One bank measured 2.1 and the other 2.5 ohms, car was cold, but when I tried to move it in the driveway, I let my foot off the clutch and the car drove a few feet then died. Restarted idled up and down, then died. Restarted Idled up and down then died again. What the heck!!!! This is driving me crazy!

Well tonight when checking everything again, tonight the car starts and runs for about 20 seconds then stalls, restarts again runs 15 seconds then stalls, keeps doing it until finally will not restart. Have no clue what is wrong with this thing

One thing I have noticed since i changed the ignition module the car wont run for more than 25 seconds, while as before it was changed it ran for 15-20 minutes. Last night i put the old module back in, and it still only runs for 15-20 seconds.. YIKES! I am wondering if I have a VATS issue. I have no codes and have it bypassed VATS with a resistor.

To find out put the old ignition module back in and replace the injectors. At 2.1 and 2.5 ohms per three injectors there is one or more bad on each side.

Once the injectors are squared away can then work on the ignition issue. Wouldn't hurt to swap the pickup coil either. They too cause intermittent ignition problems. And while the distributor is out can replace the O-ring seal to stop the oil leak at the back of the engine.

RBob.

Ok, the old module is back in and I have also swapped computers. Same result. Car starts, runs fine then 20 seconds shuts down. No codes, no security light on. Coil is new too. Seems when I try to give it throttle, thats when the stumble happens then dies...checked FP again. 42 PSI to start, then drops 3 to 4 lbs, but when car dies FP is steady and hold pressure. Should I try to block EGR tube to intake with a plate?

You could try to block off the EGR, but if it were stuck open (even the smallest of the 3 ports), you wouldn't even get 20 seconds out of the engine.

It can't be a security issue unless the light is dead, because, as I understand the Tech Article on this (and I have to pay attention to this because I have a current code 46 and a dead car until I get a VATS module installed), the VATS will disable the ECM if there is a VATS problem when the ECM is first introduced to battery power (assuming replacement ECM, of course, with the security problem already existing and not putting the 30Hz signal on pin "L" of C207 and then on to the ECM). If there is a VATS fault after the engine has started, the VATS will continue to allow the engine to run even though a fault exists.

But, VATS aside, now I am looking at something odd. You said that the car is a 5-speed. Does it have something known as a deceleration valve? This is a valve that opens when the throttle is abruptly closed to allow extra air into the intake to help stave off the hydrocarbon (fuel) spike that occurs with rapidly closing the throttle during shifts. I don't have one, so I couldn't tell you what it looks like, as I have never seen one. However, it is described in my FSM.

Also, another thing to try is to try running the engine with the timing bypass connector disconnected (setting a code 42) and seeing what happens.

How did you make out with the injector replacement?

RBob.

Should be your next step.

Injectors replaced. Same problem, car starts runs for about 20 seconds then dies. I have spark and fuel. Maverick says block EGR and his thread indicates that may be the issue, so ill make a plate for the intake Should I block off any other place? Also the decelleration valve, Ill check my FSM to see if it gives a location. But this stalling problem happens even if I dont touch the throttle. I appreciate everyones help with this.

The '91s don't have a decel valve, so don't worry about it.

For EGR blocking, easiest to do it at the intake plenum neck. I thought you did this back near post #18?

What injectors did you use for replacements? What did they ohm out to when done?

RBob.

I repaired the hole and reconnected the tube. I can make a plate. BWD brand new injector. Ohms reading around 12.2

Why am I getting the feeling there is a large vacuum leak somewhere and/or the MAP signal still isn't right? New injectors, new ignition parts, and even a new ECM, and it runs worse than when this started.

I'd also check how my valve covers, PCV valve (and the tube end at the back of the intake manifold down near the dizzy base), PCV tube and grommet on pass side valve cover, and even the valve on the charcoal can are sealing. That would be if things still weren't right when I blocked off my EGR tube. I would also check to make sure I didn't cut any of the injector o-rings upon installation (I lube them with oil when I am reinstalling the rail).

Very possible. Especially since when he steps on the gas is died. Or it takes 10-15seconds for it to die.

MAP sensor is new also, possibly got a defect? There is that one tube comes from the back of the plenum to the base of the MAP sensor and there is a 3 wire connector. How should I check map signal? Also something interesting, when I have the key on, engine not runing and i turn the a/c on the cooling fan does not work. CTS is new. I know fan works because when I hook up my scanner and run the diag test, it turns the fan on, and it runs. With my 5.0L the fan will come on with the a/c request, does the 3.1 L work different?

For the MAP, remove it from the bracket and, while trying NOT to break the vacuum line, move it in a direction where you can get a DMM between the green wire and the black one (or any ground point) with the key on. If you have a vacuum pump, you should apply some vacuum to the MAP to see what happens to the reading.

For the fan, I believe that the ECM has to see an engine speed signal in order to turn on the fan during an A/C request. Either that, or the A/C system is either empty or has a ground problem on the fan pressure switch. To test, there is a switch on the A/C line running down the inner fender well on the passenger's side, near the air cleaner. Disconnect it and see what happens... The fan SHOULD turn on when the switch is disconnected.

BTW, how many injectors did you replace?

What reading should I have at the MAP? As far as the fan, my other 91 with a 5.0, turns on with the a/c on and key on engine not running. I dont believe it should matter if it is running or not. My sons 3.1 L I know the a/c works blows cold and has freon in the system Ive checked with a gauge set. Ill try disconnecting the switch. I replaced all 6 injectors.

Ok, I disconnected the switch, the fan still does not operate. Also the MAP voltage is 4.94 when the car is cold. Now the car doesnt want to seem to run at all... UGH!!!!