GaryDoug

You can never reliably use anything but 100% alcohol (no water) to clean circuit boards. Any amount of water will become very conductive with just the slightest amount of impurities, including the material being washed away. The fluid will be left underneath components and not evaporate fully leaving a conductive layer on the surface. Even the residue layer not underneath components will be difficult to remove. Water can be under 10 ohms/mm of resistance which can swamp out circuit impedances of many kilo-ohms or greater. I am a guy who has worked for over 40 years in the electronics manufacturing and rework environment. Trust me.

Injuneer

He doesn't need a Chiltons.... Rob/Shoebox has all the factory wiring diagrams online. Very minor differences between 94 and 95.

4th Gen LT1 F-Body Electrical Diagrams

4th Gen LT1 F-body PCM Wiring

JSkeet

A friend has urged me to swap the battery ground since it's easy and I can find a suitable spot to mount one up top somewhere easily accessible.

Before I go swapping the PCM I'm going to replace both battery cables and if that doesn't fix it I'm going to troubleshoot the Opti again.

I wonder if I hook up my meter to the battery and watch voltage while the car is running if it'll taper off until the engine dies? I'd think I would've noticed radio being intermittent or lights/gauges dimming... but come to think of it, I've not been driving or running the car w/ the radio on due to the beautiful noise of the exhaust, and I don't drive at night (because the car is so unreliable) so I'm not seeing whether or not the lights dim during this plaguing issue. I'd think though that it would stumble/buck if losing power though, and it literally acts like you turned the key off.

Thanks for that tip! It's a cheap try.

As for what I used to clean to circuit board, and what I left to dry, I have no qualms over my procedure.

I used 2 cans of this:
02130 -- QD® Contact Cleaner, 11 Wt Oz

Then very little 91% alcohol on q-tips to mostly clean the orange seal between the two cases. The PCM was no worse off than before the cleaning. So I didn't bother anything inside.

JSkeet

So I swapped the PCM with a freebie I got from a tuned '94 Z28 M6, same as my car, and it did the SAME EXACT THING.

I discovered a pink wire with a splice connector on it, on one of the harnesses.... for no reason. I got the shop manuals out and discover this pink wire (#30 on red connector I believe) is for the ignition!!!!

Makes sense that this wire w/ splice connector could very well be the culprit. I'm guessing someone used it for a tach signal or something in the past?

Anyway, remove splice while car is running and jiggle. Car stops.

Could be just a coincidence.

Cut/strip, butt connector, heat gun, problem solved, right?


No. Car starts and still shuts off intermittently.


Curious about battery cables I add an extra ground from the battery to the ground stud on passenger wheel well. No change.

Pull under-hood fuse panel apart to investigate - there's a 10A IGN fuse in there, wondering if the wiring to it may be bad. Start car, jiggle all that, inspect thoroughly, nothing. Car still intermittent.



Button it all back up, put everything away, start car and it runs for 45 minutes w/o issue.



I'm wanting to chase this #30 wire, so I look in the shop manuals and it says it's tied into the MAF, COIL, and something else. I'm really thinking it could be the culprit.

Am I on the right track or is this sounding more and more like I need to do the Opti diagnosis?

Injuneer

There is no wire on pin A30 (red connector) and there is no pink wire on the red connector.

There is a pink wire on pin B30 (black connector). It is "PCM Ignition Feed". That doesn't mean it feeds the ignition.... it means it is the key switched ignition power supplied to the PCM. It is supplied by fuse #5 at the end of the dash panel, and that fuse also supplies power to the theft deterrent module, the mass air sensor and the fuel pump. Disconnecting it disconnects the PCM from power, so it's likely the engine would die. There is an inline splice as part of the factory wiring, and the splice is where the MAF sensor and pin D3 (also "PCM IGNITION FEED") connect.

There is no way that wire could be used for a tach signal.

JSkeet

You are correct then, my mistake, black connector.

Well, I assumed from the age and the fact it was a nice 3M splice connector that it was OEM but I wasn't sure, alas, there was no spade connector stuffed in it or signs of any nearby wiring that may have been intended for use there.

So, you're saying it should've had a wire connected to it!?



At this point I'm 99% sure it's going to be a wiring issue somewhere or an opti.

All the intermittent wiring issues I've ever dealt with at work end up being something just like this - fight it for months (years in this case) only to find 1 wire loose somewhere.

Injuneer

I can't tell you if it's the factory splice or something someone added. The shop manual shows a black dot with other wires connected, which indicates a splice, but it doesn't show where it is located with respect to the PCM.

JSkeet

I'll have to get the shop manuals out later and study it a little better. The splice was about 6" off the harness @ the pcm.

Mine certainly had that splice connector and nothing going to it. I wondered if it was there for resistance or something. (shows how much I know)

Anyhow, I eliminated it because I felt it may have been the source of issues and I was wrong.

But, that wire sparks concern for me, now that I know it's role, I want to chase it and make sure it's good and clean all the way.

GaryDoug

The 94 shop manual calls that splice S132 (8A-11-5) and describes the location as "Engine harn, approx 2cm from clip near PCM and main branch" (8A-11-19).
There is another pink-wire splice upstream called S205 for fuel pump relay and TDM, closer to the instrument panel.

I seriously doubt that GM would have used a 3M connector. Everything on the car is Delphi.

ACE1252

You mentioned that the cd player goes back to song #1. Does it do this everytime it shuts off?

If so, I think this is either a power distribution issue or there is a short/open happening that is causing voltage on the PWR ACCY fuse 7(15 amp) to drop to zero(or low enough to reset the radio memory). That is why the radio memory resets.

It sounds like you have a wire that is shorting(to ground)/opening due to vibration. That would explain the car just dying. I suppose it could be either open or short. A short would have to be able to handle some serious current for a short period.

A good multimeter with a MAX/MIN function can help you verify this condition(as opposed to having an opti issue). All of the better Fluke meters have this.....you put the leads on the terminals(wire going to PWR ACCY fuse panel), then hit MAX/MIN. When the problem happens, you can cycle the MAX/MIN button to see what the voltage did....if you see the MIN as 0 or some low reading instead of ~11-12 volts, then you have an intermittent open/short somewhere.

A DC amp clamp could really be useful(with max/min), that might show the current spike of a short(if the update rate is quick enough) and it might help in showing the current dropping to zero of an open. This could help to localize it to the circuit causing the problem.

From there it would be very careful inspection of the circuit and all devices on it.

Intermittents can be a pain to troubleshoot, but I think you need to look at the wiring very, very carefully.

JSkeet

That's some good info/advice.

I have a nice Fluke multi as well as a clamp meter... just not a ton of experience using them. I do know how to set min/max, use A/C, D/C, ohm check. So all that shouldn't be an issue.


It has been suggested that the ICM may be bad (again). I'll take it in for testing at Advance Auto ASAP.

JSkeet

Oh, and, I'm not 100% sure the cd player always resets to song 1. I'll have to monitor that closer next time, as I only noticed it a time or two.


When it has died on me though, while in motion, clutch starting it has never worked. It's a total ignition failure of sorts.

Injuneer

I mentioned this way back, but it didn't seem to be understood. When I got this cryptic response indicating just the opposite of what I said, I gave up:

JSkeet

I don't know these cars a well as you guys, nor am I a mechanic, some things are lost in translation.

I hear "high voltage coil wire" and I went and inspected the wiring right at the coil. I hear "power supply problem" and I think, bad PCM.

To be honest, I had forgotten I even owned the shop manuals w/ diagrams and all... but even having them I'm not a trained eye who is great w/ schematics... if I was, I probably wouldn't be here asking for help.

Relax and bare with me or write me off as a dip**** and move along. I'm just looking for some help/advice.

pkincy

You can chase your tail for years, or you can buy a Helms manual and a MultiMeter and chase every wire in the car with the Helms open in front of you.

But first: Re: the PCM. Be really nice to someone near you that has a 94Z28 without mods and borrow or rent their PCM for a half hour. Install it and see what happens. If that solves your problem you know you need a new PCM. If it doesn't started checking Voltages.