Good afternoon,

1994 base model automatic. Got the vehicle up and running about 5 months ago after sitting for a while (see my other thread for more details). Have not driven the vehicle for the past 6-8 weeks as I've been busy with life and performing interior work on the vehicle. New center console and shifter boot installed thanks to tips from this forum.

Today, I put the vehicle on the battery charger as it was dead, then wanted to take it for a drive simply for the sake of running it. Ran the vehicle for about 45 minutes with no issues. When I pulled back into my neighborhood, the car stalled on me with no warning. It started right back up, but the engine was surging- up and down fairly quickly and constantly between 200-2000 RPMs. The vehicle stalled again after < 10 seconds of running. I had a paperclip in the center console- jumped the OBD connector and it's not giving me any codes past or present. Opened the hood and checked for any loose wires that may have become disconnected. Everything looked good. Turning the key half way to start I can hear the fuel pump whirring. I was able to get the car back to my driveway (50 yards away ish) and it stalled again. Started one more time to get it into the garage where it stalled again. Put it in neutral and pushed it the rest of the way in.

Any tips on where to start with diagnostics?

Vehicle did not overheat while running. Hottest coolant got was about 215 I always watch it.
Once the car was fully warmed up, I took a couple medium pulls on it, but RPMs never exceeded 3500 and never went passed 60 mph.
Some info about the car:
New fuel injectors, pressure regulator, and filter last year.
New EGR and canister purge valve solenoid last year.
New Petris optispark, Delphi ignition coil, wires, and plugs around Christmas time.
New water pump, thermostat, hoses, and coolant temp sensor last year.
Coolant flush a few months ago. Reused knock sensors.
Took it to a shop a few months ago as it had a rough idle- they diagnosed an aftermarket camshaft installed by previous owner I didn't know about and tuned the vehicle on dyno.
New driver side O2 sensor a few months ago. I have the passenger side- have not put it in yet.

Since the tune, I've driven the vehicle maybe 150-200 miles without any issues until now.
I am aware that Petris makes the best optispark you can buy right now, but even then sometimes they fail. Anyway I can diagnose this before tearing the whole front end apart? It's still in the 1 year warranty period.

 

Sounds similar to my '94's behavior about 10 years ago. Driving down the interstate, middle of August, withe engine running around 128 degrees or so with A/C on. The engine would just stall and die, left me stranded on the side of the road. Wait 10 minutes and the car would start, run about 5 minutes and stall again. Wouldn't start unless I waited, which I assume was to let the engine cool. Made it to the Chevy dealer and no codes were pulled, and they thought everything on the car was normal. I had them install a new Ignition Control Module and new ignition coil and that fixed it. You might want to check your ignition control module. There's a thermal paste insulator to thermally isolate it from engine heat. If that paste gets hard or brittle, the engine heat will fry the module.
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Check your fuel pump for crud. I (unknowingly) had the sock come off the pickup. Pump packed with crud over time, eventually would overheat the pimp. Let it cool down and it would start right up again. The longer we let it cool, the farther we could go until the next stall. Eventually replaced the fuel pump and sock and it has run 12 years, 17,000 miles, with no problem. Not saying you have the same problem but worth at least looking at. Put a fuel pressure gauge on and see what it shows when the trouble starts.

 

Any updates? Come up with a cause yet?

 

Worked a half day today and had some time to do diagnostics.
I pulled codes again and it was giving me H16 (optispark).

Unplugged the battery for a few hours to let the codes reset. Then I ran the car again for about 45 seconds.
The surging / stalling is definitely not related to engine temp. Fired up no problems first crank with the engine cold, but immediately began surging up and down between 1200 rpms and basically 0. Every time it would hit 0 like it was going to stall, the engine would surge back up again. Could smell gas and there was audible backfiring. Shut the car off.
I pulled codes again. H16 gone, but there is now H64 (bank 2 lean).

I had replaced the driver side (bank 1) O2 sensor a few months ago as it had failed. I have the passenger side (bank 2) O2 sensor sitting in a box just haven't gotten to it yet... I guess now is the time.

I checked the fuel pressure with car off key on: 37 psi and holding for several minutes.
I started the car and kept the fuel pressure gauge on: holds at about 37, jumps up to 40-42 when I manually unplug the pressure regulator vacuum connection.
The car responds approx. 50% of the time when I hit the gas pedal- sometimes the tach will jump up appropriately, sometimes it just stumbles.
Shut the car off after about 1 minute of running (did not stall out- just surging as before).

Checked voltage and ground at distal end of Optispark wiring harness. All good- 12v, 5v, 5v, and 0 ohms as appropriate per service manual.
Checked voltage and ground at ICM wiring harness. All good- 12v, 12v, 0 ohm, and 1-4 AC volts while cranking key as appropriate per service manual.
Called around all the auto stores around my area- none of them have the equipment to test ICM or ignition coil on the bench. Multimeter to ignition coil reveals appropriate continuity and resistance- that's the best I'm gonna get for testing it.

I replaced ignition coil with Delphi unit < 500 miles ago.
I have not replaced ICM, but it is AC Delco and I proactively cleaned and reapplied heat sink paste < 500 miles ago.

I feel very confident ruling out a fuel problem at this time and pretty confident ruling out ignition coil or ICM.
I put the car up on jack stands just before coming inside to write this. I will go ahead and replace bank 2 O2 sensor first thing tomorrow. I've already got it and I should do it anyway to match the bank 1. But, I really don't think this will fix the problem. Unfortunately, I think I'm looking at Opti failure. I've already given a heads up to Petris and so far they have been super great with customer service- as soon as I let him know he's willing to ship it back for me to test it.

 

You are doing a fine job of providing information! I'm far from an electrical guru but the opti seems like a likely culprit.

 

I have switched in the passenger bank new O2 sensor. Petris has been very helpful to me. Shipped the Optispark back to them and they tested it- no problems with Optispark. I got it back in the mail yesterday and will be putting it back on this weekend. He actually emailed me back and recommended checking grounds for the PCM. Clean / replace if needed.

New plan of attack (progressing as needed):
1) Re-install the Optispark. Start the car and see if problem is fixed with new O2 sensor.
2) Check, clean, replace PCM grounds.
3) No codes for it and nothing in particular to point me this direction, but it's free: back probe TPS, MAP, and MAF sensors.
4) Replace ignition control module. Checked out okay, but this was the only piece of ignition system I have not replaced.
5) Petris does scheduled consults for diagnostic help. Pay for this and go from there.

 

Optispark is back on. Ran car only for about 20 seconds (serpentine belt and water pump not back on yet), but it did not have the same problem as before! Will put water pump and everything else back on next week, but hopefully the O2 sensor fixed it!

 

I put the water pump on yesterday, allowed the paper gaskets coated with RTV a full 24 hours to cure, then put all the hoses and connectors back on today.

The car is no longer starting. It will crank and crank, but no start.

I pulled a spark plug wire and put a spare plug in it, no spark seen.
I'm still getting correct readings at optispark wiring harness and at ICM wiring harness.
Most likely scenario was that I injured a wire somewhere putting the water pump back on. There's a ground wire bolted to the block on passenger side just next to the water pump. I undid this, cleaned everything, and re-attached. Ohmed okay from ICM harness to this wire so I can rule that out.

I was just about to pull the wire from ignition coil to opti and check for spark there, but the key is now stuck in "on" in the column. I can twist to crank the car, but cannot twist back to off or lock to remove the key. Tried twisting the steering wheel, wiggling cylinder in/out, and playing with shifter (automatic) to make sure it was in park for about 30 minutes. The key will not budge.

Next step is to remove steering column to replace the ignition tumbler. Have to do this before checking anything else out around the front of the engine. Any ideas for what else to check while waiting for tumbler to come in?

 

Waiting for parts and going online for more info / diagnostic help. This video helped me quite a bit when it came to decision making.

This is very similar to what I'm experiencing.

After the steering column / ignition cylinder is sorted out...

1) Triple check opti spark harness signals
2) Triple check ICM harness signals
3) Look for spark directly at ignition coil
4) Check grounds. Does anyone know where the ICM and PCM ground to? I assumed ICM was to the engine just to the side of the water pump, but I'm not sure? Continuity from ICM harness to this bolt/wire was 0. Continuity from ICM harness to battery negative terminal was .5 ohm. Definitely a connection there, but not sure if I should see a bigger drop to 0?
5) Confirm injectors firing with noid light. From what I understand, opti failure (at this point slim to none) would cause lack of injector pulse, but ICM failure should still allow injector firing.

I really am stumped. The car suddenly driving very badly a few weeks ago after driving about 30 minutes makes me think it might be ICM, but it never had any problems at all starting until today. Before any serious diagnostics when this just started, I waited a full day for the engine to cool off and with battery unplugged to reset everything. Fired right back up immediately, but the problem was still there. Last week, after confirming the optispark was not the problem (see older posts) I replaced the passenger O2 sensor. After putting optispark back in, the car fired immediately and ran smoothly for about 20-30 seconds. I thought I was in business so yesterday and today put the water pump / hoses back on. Now crank no start. Could the ICM suddenly fail after fixing another problem? Could the ICM have been the cause all along with just sporadic acting up (making me think O2 sensor was the fix), only to completely fail now? The ignition cylinder locked up after repeated cranking for diagnostics of no start today- is this failure somehow oddly connected?

Too many moving parts. It's starting to sound like some conspiracy. It's just a machine. I'll get it fixed.

 

More updates. New key cylinder is installed. I can now crank the car safely again (and turn it off and remove key!) allowing for more data.

1) Confirmed fuel injectors pulsing with noid light. This proves optispark signal is getting to PCM and this proves fuel is not the problem.
2) Confirmed no spark condition with spark tester at coil.
3) Checked ICM harness and this was an issue...
ICM Harness readings:
A) 12Vdc
B) 1-4Vac during crank
C) 0 ohm ground to front of engine
D) NOTHING. No signal. 0Vdc.

At this time, it seems that terminal D is a very likely suspect for no spark condition. Right after installing the water pump when it gave me the no start condition first, I could've sworn I was getting correct readings at ICM terminal. Maybe emotions got in the way and I read the wrong terminal? Maybe it's an intermittent problem?

I'll get to my library this week and borrow the service manual again to trace back the wiring. Maybe it's a fuse, but it seems likely I injured the wiring while putting the water pump back on. Done for the day and happy with the progress.

 

Best of luck. I really admire your patience and persistence. If that was my car, odds are I would have torched it about three days into it

 

Okay I think I've got this figured out.
Based on the wiring diagrams, the earliest in the chain for power should be the fuse and the last in the chain should be ICM.

At ICM terminal:
I had 12V at terminal A
I had 0-5V AC at terminal B
I had 0 ohms good ground at terminal C
I had nada at terminal D

I checked continuity to terminals A and D from the fuse. 0 ohm to A. Nada (1- open) to D.
Okay that's one step closer.

I went back a step in the chain and checked continuity from ignition coil terminals to D. Good to pink/black at gray connector. Plugged gray connector back in and left black connector unplugged.
Where the black plug goes into ignition coil, I checked for continuity there to fuse. 0 ohm to the terminal for pink/black at black connector (going to terminal A ICM). Nada (1- open) to terminal for dark green at black connector (going to terminal D ICM).
Interesting.

I unplugged the gray connector and jumped it straight to the black connector with a paper clip and some alligator clamps. Did the pink/black at black connector first and got 0 ohm from fuse to terminal A ICM. Did the dark green at black connector and finally got 0 ohm from fuse to terminal D ICM.
Alright problem identified- signal not getting through the coil.

I had an old coil sitting around from last year. Undid the power steering reservoir and swapped in the old coil.
Plugged everything back up and ran my checks again.

I am now getting 12v DC at terminal A and terminal D ICM.

Proceeding with no spark decision tree, I crank again and look for spark at coil with tester. Still no spark! (It is worth noting that when this coil was taken off last year, it was working fine. It was replaced when I was trying to fix a misfire. It wound up being an O2 sensor and aftermarket cam shaft I didn't know about, but that's a different story. Point being: no reason to believe the coil is the cause of no spark at this point.)

I got power to opti. I got signal to PCM. I got PCM processing signal and sending to ICM. I got good ground. I now have 12V DC at both terminals A and D.
Manual is pointing to ICM as the cause. I have no idea how the coil shorted, but I suppose it's possible when the ICM failed?

ICM getting ordered today. This is nuts lol.

 

Back up and running.

ICM came in the mail.
Slapped it on with new thermal paste. Filled with coolant. Took down from jackstands. Started first crank and runs great now.

Problem solved- was likely ICM all along slowly dying and somehow it fried the connection in the ignition coil giving me no power to terminal D