Hey Friends! I am stumped. I recently purchased a 305 TPI 87 IROC with 40k miles. I drove about 75 miles and died. I traced that down to a fuel pump issue and replaced it. It was running pretty well except the o-rings on the fuel rail were leaking because I put the wrong ones in while trying to diagnose the fuel pump issue. When I put the right ones in (I think - they are orange) the leak stopped but then it started to idle terribly and has eventually now degraded to won't run at all. It still starts. I found a code 34 stored but not sure when that showed up. I thought for sure I forgot to connect a vacuum hose but I've taken the plenum off and re-checked a few times. At this point I have replaced: all 8 injectors, fuel pump, IAC, and MAF. Fuel pressure is fine at the rail last time I checked. I took the fuel rail out again today to see if something was in there or the o-rings were dislodged. All seems fine.

Any ideas?

Thank you in advance,
Tom

 

What did the inside of the tank look like? Pull the fuel filter and blow backwards through it onto a paper towel. See what it looks like

 

If fuel test above is Ok id look at spark / ignition control module as those are known to go bad

 

Thank you. Forgot to mention, tank is new. When I replaced the fuel pump and sending unit I emptied the tank and cleaned it out. I also replaced the fuel filter.

 

I didn't check any spark-related things, though.

 

I would verify your fuel pressure. I've seen those pumps get replaced and the pulsator or the hose in in its place on the tank fail. Also, I've seen the sock fall off and create starvation issues

 

will check the pressure again

 

Reliability of pumps these days is not the best either.

 

Phew... alrighty... I've replaced, the EGR valve, rotor, cap, pickup coil, IAC, TPS, MAF, ignition coil, and ignition module. New moroso wires and new plugs. I cleaned up the distributor while there. I aligned the rotor with the little dimple on the distributor helical gear when I put it back in. I rotated the engine manually so the etching on the harmonic balancer was aligned with 0 degrees on the metal timing marks attached to the balancer and ensured the rotor was pointing toward the electrode of the cap that would fire cylinder 1. Fuel pressure on the rail seems fine though it does leak down slowly. All 8 injectors are new as well.

Still doesn't want to run. it tries to turn over and run. Sputters a bit but dies pretty quickly. Also I found a disconnected plug that I am unsure where it goes. See pic below.

Does anyone know what the plug is? Did I miss something else?

Best,
Tom

 

Also wanted to mention I verified that cylinder #1 was on the compression stroke and aligned the rotor to fire that cylinder first and adjusted the harmonic balancer to TDC. So, I think the ignition timing is close enough to run (maybe not great though). I checked some fuses under the dash because the fuel injectors have a few fuses. those were all fine. starts but will not run. it behaves about the same as it did before i replaced all that stuff!!

 

Will it run any further if you spray starting fluid down the intake?

 

From what I can tell this picture is looking up from the bottom drivers side back of engine. If so you have electrical connections from the main harness that goes across the top rear of block for the distributor/coil, intake air temperature (bottom of plenum) and oil pressure switch (back of engine behind distributor where intake joins the block). See if all these are connected and if not you found where it goes. Also code 34 is for the Mass Air Flow sensor .

 

Thank you. I know the plenum one is connected since I just put that back together and there are no free openings to the distributor. So that only leaves the oil pressure switch. I'll check again.

Ratfink, I tried the starter fluid and couldn't tell initially whether the fluid helped a bit or having the MAF off. I think I isolated to having the MAF off helped it start and run. Though it ran very, very rough and idled around 500 RPM. When I gave a little accelerator, it would rev a little to about 1200 RPM I heard one or two random pops. It idled for a minute or so before I turned it off. I was able to get it to start and run roughly at that 500 RPM idle consistently with the MAF off using fluid or not. Once the MAF went back on, using fluid or not, it would start but die immediately. I didn't hear any mechanical knocking of any kind. Also, got a new Code 33.

Thank you both for your help,
Tom

 

that disconnected plug has a red and black wire going to it. doesn't seem to want to travel too far.

 

Code 33 is for the MAF sensor.
The ECM thinks the engine is getting too much air for having a half to completely closed throttle valve while being in the lower RPM range.
Would explain why the engine would run when you disconnect the MAF, since the ECM then uses a default value to base its fuel metering on.

Here's the diagnostic chart from the 85 service manual as I don't have one for 87.
May give you some new ideas.

 

So you can get it to run now? Have you verified timing? With and without the tan/black wire disconnected?

 

Well, it runs w/out the MAF - just terribly. I have not verified any timing up than setting the distributor to fire on cylinder #1 with the harmonic balancer at TDC on the compression stroke. But if the timing were slightly off wouldn't it still run reasonably well just not optimal? I can look at the trouble tree. Do we think it is possibly a bad MAF sensor? It is brand new.

Best,
Tom

 

Check the timing. It can be way off and still run... just poorly. Running poorly due to mechanical issues (like improper timing) can cause false codes. You need to go after the cause, rather than the effects.

 

Roger. will do. Any idea what that connector is this is disconnected? Maybe it is important :-) red (or pink) wire and a black wire.

 

I do not recall off-hand. If you pull it up into the engine bay, does it have a longer reach than where it's currently dangling?

 

The only things I can think of for that connector is either one of the connectors going into the ignition control module or something going down to the transmission.

 

It has two wires, one is black and the other is pink with a black stripe. it goes back to one of the relays/connectors in the driver's corner near the firewall. it isn't long enough to run down to the transmission, though.

 

wiring diagram for the 87 5.0L below. There are quite a few pink/black wires...?

 

you may find that the connector in question is the 'extra' connector that goes no where

if so it will have a simple hot and ground lead

 

I would be happy to know that. Are you seeing "extra" in the wiring diagram?

 

Did you ever try to find where that connector is dangling from? It may reach something up top and maybe become more obvious.

Also, there's usually a big difference between pink and red on a GM car. Pink is usually ignition power, red is usually constant power. Not always, but usually.

You also can test for power and ground at that connector. Depending on when it has power (if at all) can narrow down the possibilities of what it may be used for.

It also may not even be engine related. It could be dangling down from the chassis harness. Might even be for the underhood light... I don't remember when they started using weatherpack connectors for those.

 

Good question. I did trace it back to one of the relays near the wiper motor/firewall. But I am not entirely sure what those do exactly.

 

In-line spark plug tester lights up while cranking. Noid lights on the fuel injectors light up (I test only two injectors - one on each side). I had a few pops or so but it still didn't want to turn over. Is this more likely a timing issue? I could try again to set it to TDC with some more advance. I'm pretty sure the last time I set it I had +8 degrees advance. Timing light didn't seem to want to do much while cranking, though.

Thanks in advance,
Tom

 

Oh! Some signs of life. I put it back to TDC with 0 degrees advance and it started and run stumbly. I turned the distributor whilst running and got it to improve a bit but not completely smooth. What's going on with it?

Best,
Tom

 

Set it to 6-8 dbtdc with est disconnected. After that plug est in see how it runs. It will advance to around 20. If it still runs rough and all tuneup items are good. Move on to fuel system or get this view ecm data.

 

I was at about 8 degrees advance before TDC and it wouldn't fire at all. I didn't try w/ the EST disconnected. is that the single tan wire? Pressure seems good at the rail and noid light test of one injector on each side was okay.

 

no real difference w/ EST plugged in that I could tell. Using the timing light and with and without EST the timing was certainly different but I couldn't tell by how much. SES Code 33 and 42 showed up but I expected those because the MAF and EST are disconnected. Initially when I started it up, the timing light showed the timing was very far retarded. As I was turning the distributor I could bring it back to a little before TDC but the idle didn't improve much - only slightly.

Also, the tach is pinned itself around 7K for some reason now and moves only a little. That's new. The engine isn't running at that speed. Sounds like it is limping along at 500 rpm.

Just to recap, IAC, TPS, cap + rotor, plugs, wires, ignition coil, ignition module, MAF, and pickup coil, injectors, fuel pump, fuel sending unit, fuel filter, and gas tank, are all new. In-line spark plug tester shows firing on cylinder 1, noid light tested on one injector on each side show pulsing.

Thoughts?
Best,
Tom

 

Tach fixed itself... not sure how it got there in the first place. I put the MAF back on and reconnected the EST. Still about the same behavior. Very rough idle barely running. Hard to tell the timing w/ the light as it hops around a lot. Turning the distributor will improve only slightly.

Best,
Tom

 

The timing is fluctuating with est disconnected?

 

Let me check. I've had it connected on the last two attempts and the RPM was so low the timing mark didn't seem very consistent.

 

I couldn't yet get it to idle w/out the EST and the MAF on. Last time I had it idling it was with EST and MAF.

 

I'm starting to suspect an issue with the wiring, as you mentioned that tachometer issue.
The tach signal is derived from pulses the instrument receives from the ignition coil via the white wire.
Circuits in the instrument cluster then convert that into a signal the instrument can display as RPMs.

Then again the ECM does work with reference pulses from the ignition coil, too, and if there's an issue like interference on the wires, it will give you totally whacked injector pulses and flood your engine... or starve it.
Follow the wires from the two ignition coil plugs and see if there's an issue somewhere, maybe even dirt or water in one of the connectors between coil and wherever the other end may be.
If that leads to nothing, perhaps suspect the ECM and try a replacement.
The ECM triggers the injectors and you said the noid light lights up, but you can't read how often those injectors are being pulsed from that light... pulse-durations are in milliseconds and determine how much fuel gets put out.

Man, I'd suggest getting a suitable ALDL cable, a cheap laptop and TunerPro with the right files to read your ECM data in real time (or ask someone with the equipment to come over and help you out, if possible).
You would be able to spot defective sensors and all the off values the ECM may be receiving.

 

Thank you! I have a friend visiting this weekend. Lets see if we make any progress. I did look up TunerPro and I'm glad you told me what I needed for the cable. I'll find that too.

Best,
Tom

 

$32b is tricky to use on the 1227165 ecm . Might try winaldl

 

do you think the wrong o-rings in the fuel rail could be an issue? When i initially replaced the injectors whilst troubleshooting the fuel pump i replaced the transfer line o-rings on the fuel rail with some that came with the fuel pressure regulator. it ran fine except it leaked a little from the fuel rail transfer lines. i then replaced the o-rings with some other orange ones I had around that seemed stiffer. the leaking stopped but it started to run like crap which lead me down this whole ignition troubleshooting. maybe the wrong o-rings are restricting fuel to the right side of the rail?

 

what ? 😝 how would that work!

 

some o rings that came w/ the fuel pressure regulator seemed to fit. so, I used them :-)

 

on the low probability chance that the o-rings were giving me some problems, I replaced them all on the fuel rail with the o-rings from kit. best I get is a choppy 500 rpm idle. advancing or retarding the distributor can improve a little or kill it. I am going to trace the coil wires back to see if any issue is there like suggested. but, other than that, should I get the ALDL cable for the ECM?

 

video of struggling idle and using timing light:
should the timing light be pulsing at the same rate for all plugs? because it isn't...

 

Do all cylinders drop in rpm when you unplug plug wires one at a time ?

 

I can try that!

 

I'd definitely get the ALDL cable, as that is an investment for future diagnoses. Mine helped me figure out a bad knock sensor, confirmed suspicions about a bad vehicle speed sensor and especially issues with the O2 sensor and A/F ratio problems.

The timing light may give you varying results as long as the EST connector is closed, because the EST dynamically manipulates when a spark plug will fire, which in turn causes your timing light to light up.
To me, hearing that engine idling sounds like a lot of manipulation is going on to keep it barely running.
Has your minimum idle adjustment screw ever been tampered with? Is the tab that touches said screw bent? That would give back wrong throttle position info in relation to the position of the throttle blades.
And if the blades are closed beyond a certain point, the engine suffocates, which the IAC valve can only compensate so much.
Again, the ALDL cable would show you what the TPS voltages and IAC step counts say.

 

Do try, but please pull the boots only using an insulated pair of pliers and/or gloves, to prevent spark pulses from jumping over to your fingers.

 

was going to mention the common sense thing

 

really hard to say since the idle was so rough. i'll try again. i tried the timing light again on all wires, though. having a hard time getting a consistent reading on the wires. sometimes the light flashes erratically on a wire (number 2 for example) but later will be more consistent and steady.