The particulars on the car are as follows:
'93 Trans Am, basically stock.

Description of problem; about a month ago, I installed a Chandler opti. While I was doing the job, I replaced the coil (it was loose in the housing), plugs (NGK TR5's gapped to .050), the ICM (broke the damn pigtail connector removing the coil) and the wires (Taylor 8.5mm).
The car fired right up, ran like a champ, and all was right with the world for about three weeks.
Fast forward to last week; on my way home from work, the engine just died with no warning. No misfire, no bucking, just died as though I had cut the key off. Immediately the engine RPMs dropped to zero, but a split second later it caught back on it's own and went right back to where it was, but now with the SES light on. When I got home, it was showing code 36 again. However, *most* of the time, the SES light is off on a cold start. After about 15-20 minutes of driving, it will die going down the road, then restart on it's own again just like before, then run in low res mode until I get where I'm going.

My research points to an opti that is suffering from heat-soak, but I haven't seen anyone describe the oddity of the car restarting itself in low resolution mode without having to actually stop and allow it to cool. When cold, the engine starts immediately. After the restart happens, it cranks like you'd expect a low-res mode car to crank. 5 seconds of turning and tapping the gas to fire off. It's just the issue of restarting on it's own without having to stop that has me very confused. Has anyone seen this before? Should I be looking at something besides the opti?

Thanks

 

The ICM can become "heat soaked"as well..Take it off and up to an Autozone or Orileys and have it tested...When you reinstall it use 3 washers on each end to space it off the head to cut down on the heat transfer.

 

Sounds fuel related.Keep posting.

 

DTC 36 is high resolution signal. Engine should continue to run on the low res signal, but the codes indicates loss of high res signal. If there is an intermittent high res signal, it may run rougher, make the tach jump around. Its the low res pulse DTC 16 that shuts the engine down, and does not turn on the SES light.

Could be another case of a poor quality Opti, but the absence of DTC 16 is odd.

 

I thought the same thing, Injuneer. The ICM could be an issue, so I am going to take it in for testing today. However, I doubt it will be the problem because it doesn't require a cooling period before restart. The engine literally shuts down just long enough to reach 0 rpm, then restarts itself as long as I'm rolling down the road fast enough. From what I know and what I've read, a heat-soaked ICM will shut down until it cools and you'll sit on the side of the road until it does.

Could the abscense of DTC 16 be due to the self-restart? If it restarts on it's own in low res mode, won't the PCM read only a loss of the high resolution pulse?

 

You didn't mention M6 or A4...

Based on nothing but words, I suspect the problem is not with the opti but with the fuel system. The engine doesn't likely get to 0 rpm and then somehow restart itself with an A4, I think the rpms drop very low and then an event occurs that allows it to run again. A fuel pump that shuts off, a intermittant ground for the relay or the pump could cause that scenario.

The lack of the DTC 16 could just be because it never lost the signal....

Just guesses....

 

It is an A4. When I say 0 RPM, that's exactly what I mean. The engine is off, no power steering, no power brakes, all dummy lights are on for a split second, no sound from the exhaust. Then boom, she catches back and fires off. Once again, prior to this, the SES is off and the car is running perfect az far as I can tell. Once the event occurs, I get the SES and a code 36 until it sits several hours.

I have tried stopping immediately after the shut down, shutting off the ignition completely, then opening the door to cut power to the accessories. Then I restarted the engine. It took several turns before it actually cranked (5 seconds or so) then the SES was on again. This was just to see if the shut-down was the cause for the SES because the SES only comes on after the mysterious restart, not right before it mysteriously dies like I would expect.

Sorry for the long posts. Just trying to provide as much info as possible.

 

I'm not trying to be condescending but you know that what you just said is quite impossible, When an engine goes to zero rpm, equipped with an automatic, it can't restart without engaging the starter motor.

It sounds like an electrical problem, a momentary loss of power, that has the gauges read zero, that allows the slowing engine to restart when power is restored. No power steering and no power brakes can be related to the slowing engine.

I'd receommend checking the ignition switch and the large gauge wire to the starter, as well as the wires on the (+) and (-)junction blocks on the inner fender. An intermittant problem can be a bear to find, try wiggling things around as you check.

I think I'll say now it isn't the OPTI........

Good luck!

 

I should also mention that it has died while coming to a stop from highway speed after 15 or so miles at least three times. However, it didn't restart any of those times. All of those times required going back to park or neutral and turning the key. But, all of those times also resulted in an SES code 36 after restart as well. Honestly, it's an A4 behaving like an M6.

 

Yes, bw, I understand what you are saying. In your shoes, I would likely be wondering what kind of looney toon I was listening to myself. Trust me, I am not dismissing your suggestions out of hand. I will be checking everything suggested and I will post my findings for posterity. However, I am nagged by two things;

1. Why does the PCM give me code 36? The engine is running like crap after it "catches back up", we'll call it. Possibly the opti harness losing connection intermittently?

2. Why does it actually DIE, requiring a restart with the key if the event occurs while not at highway speed? i.e., coming to a stop for a turn.

I've been a member here for years, doing my own mechanic work and I never post anything. I research everything with the search function and don't clutter the boards. Notice I haven't said that I started randomly replacing sensors or parts, either. Gimme a little credit, man, lol. It just happens that I'm stumped this time.

As far as the impossible rolling start, yes, I know automatics don't do that. I just know that if it's just going to low rpm and not actually shutting down, it's so low that I can't hear anything from an exhaust that has no cat and no muffler. I hear nothing but tires on the highway. I know you've got to be right, but I can't figure out what I am experiencing.

 

I'd check the opti harness. If your gauge cluster does not go dead (no lights or anything), I would not suspect the ignition switch. I'm not sold on Chandler optis, either. A 36 is going to be the opti or opti harness.

 

DTC 36 is the Opti or the Opti harness. More often than not when the High Res signal is lost, the motor will die, or come very close to it. It will fire right back up with an extended crank with the SES on. If it's not the harness itself, your Opti is on it's way out.

This is normal behavior with an intermitent code 36. I have the exact same issue with my 94 and simply have not replaced the Opti....again.

Actually, they can

 

How so?

 

Same way a manual does, you just have to be going a whole hell of a lot faster. More than likely, though, was that the motor simply caught at the last second. When 36 sets, the motor loses spark for a short amount of time. It's a craps shoot whether or not it stays running.

For the most part you are right, it's not an easy or common thing to do with an auto.

 

The tach is going to drop to "0" on loss of the Opti signal. Does not mean the engine has stopped turning, only that the RPM signal was lost.