I think it's Opti TIme.

I have run the car through probably 10 cycles of "get HOT, then die". It is like clock work. With the hood closed, one fan cycle and it dumps. With the hood open and cool air, it can take a couple fan cycles, but at any rate heat = no spark. This afternoon, I would hold the throttle so that (when the symptom started) it would run about 2k...the idea being that there would be a great chance for it to stay running. Due to longer "coast time" it did help...but when it finally crapped, the Low res signal had long since vanished, and the hi res stopped counting.

One odd thing is that when it's cold/cool, I still get codes 13, 16, and 42. If I clear the codes, they come back instantly...even though when cold, the thing LOOKS like it's working.

At any rate, I've had every connector off and on multiple times. I'm confident that they're all making a fine connection. I can feel the pins engage the female pins as I slide the connectors together. I've tried wiggling; no diff, hot or cold. It is totally heat related.

The other thing I wondered was if the ECM was being affected by heat. Since the hood closed sped up the symptom. Anyway, with the car cool, I ran the hair dryer on the ECm until it was about 180*F...car started right up and ran fine (until engine got hot again).

One last thing; because I keep getting a code 42, I tested the white wire from the coil to the ESC at the ECM to ground. I got ~1.5 M ohms. Not a short...but there is continuity there. I ohmed the wire from the ECM to the coil and got 0.02 ohms there, and then from the ECM to ground and gor the same ~1.5 M ohms. Any thoughts on that?

At this point, I've drained the coolant and pulled the water pump and balancer. Time for a new distributor, I guess.

 

Yes, I agree, I think it is Opti-Spark time.

The 1.5 M Ohms things, umm.......that is a lot of resistance. I would like it better if it read OL, but I don't think it would cause an issue. Possible but the sun might not come up tomorrow either.

 

1.5Mohm, yeah, I am going to say "thats fine".

Your scan tool sounds a little screwy if it threw out all those codes! Id call it a fluke on those.

Probably need a new MAT.

22mSec... lets see 22msec between each start of the low resolution trigger, so it reads the leading edge. There are 4 slots, so multiply 22mSec by 4, 88mSec per rpm. but wait, the cam turns at half the speed as the crank... so divide by two... um wait if there are 88msec for half a crank rotation... or 44msec per rotation
44msec*1000=4.416666 sec
4.416666sec*60=265 rotations per min
265rpm of cam*2= 530 rpm on the engine. That cant be right

Factory settings:
Auto - 550 in drive, 650 in park.
Manual - 850.

so what does this 22 number really mean?

Well this isnt relevant at all. just a head scratcher... i tried frequency, i come up with .22Hz at 530rpm, .14hz at 850rpm.

either way, that low resolution signal just needs to be there. if it is=good, if its not=bad

did you try this on the ICM when it was dead?

 

I'd like to learn more about the count number on the low res. Just so I know, but you're right; "000" doesn't seem good.

I didn't try Step #7. I wish I had thought of that and tried it but I forgot. Now it's apart, so I can't get it up to temp. I'm GUESSING that with no low res dignal on the scan too, and no high res signal, there wouldn't be a pulse signal at the ICM, but that is...a guess.

 

Yeah, no low res. and no high res.=No pulse. ECM does not know how fast engine is going, or anything.

Can run without High, but NOT low.

From 93 FSM, paraphrasing, Low Res. (4 pulses per crankshaft revolution)
Figure displayed is time difference between the pulses, in m/sec.

I would believe that "000" is an error readout. That could never logically happen under normal operation.

 

That is interesting...and good info. Thank you. I wonder what the deal is with the "000" too. It will start going to that when the symptom starts, and for the last 5 seconds that it will run or so, it only shows "000"...while running REALLY badly.

Another thing that indicates that there is ZERO crank/cam reference is that right before it dies, the fans will shut off...then if it fires again before coasting to a stop, the fans kick right back on. I'll keep you posted...

 

Guess I need to read my fsm more... lol. I've been going on memory, which seems to be running low this week.

 

......... Try running a ground wire ... heavy gauge ... from the battery to the engine ....... jumper cables would work for testing purposes ..... multiple codes are sometimes caused by a single problem unrelated to the codes being set ..... it wouldn't hurt to include the ECM in the ground loop ..........................

 

Tom, get er running, We want to come down one of these weekends and play race cars with you.

 

I'm workin' on it Wayne! Well, another day off and it's time for an update:
I really do hate to say this...but it would appear to me, that the above is not true. I've ordered a new "opti unit" and it is en route. Meanwhile, I was still feeling uneasy about the extremely strong correlation between heat/symptom, my diagnosis that it's the opti unit, and Merlot's statement above. 1 of the 3 didn't fit.

Today, I took the distributor off the front of the motor. Took it apart, and reconnected the wire harness to it. I ran my coil wire from my coil to near ground, and then with the Key On, turned the distributor wheel and everything "lit up". The coil wire shot sparks to ground, the injectors fired, the AIR pump started up, fuel pump ran...everything happened that would happen if the engine were running (correctly)...as predicted.

THEN, I took the stripped down unit into the house and threw it in the oven, 275*, for 15 minutes. Came out baked to perfection! I cruised out to the garage with it in hand (leather gloves) and plugged in the harness, turned the key on, and spun the optical wheel with the screw driver. See video here:




NOTHING!.
Dead as a door nail. Everything else in the car at this point is "room temp, EXCEPT the dist casting, and opti unit. For further "proof", I let the unit sit w/o touching it, still connected to the harness, cooling for about 10 minutes...then I spun the wheel again and BANG! Everything "lit up" again; spark, injectors, fuel pump, AIR... I ran the test twice and the point that it begins working again during cool down is roughly 208*F...about the same as on the car.

It would seem that heat can affect the unit. I can prove it on mine clear as day. NOW I feel good about my distributor replacement. I know for certain that is the issue.

 

Must be the support circuitry? The diodes themselves shouldn't die under heat.

I suppose its my turn for humble pie?

Either way, glad you got it figured out. That rust leads me to believe there was some water in there at some point!

 

Ha ha...well, let me tell you from EXPERIENCE...humble pie varies in taste greatly, depending on the origin! Lol.

I still appreciate your posts and the diagrams are interesting too. It IS a simple piece. It's possible the the problem may not be in the unit, but maybe in the rest of the assy? Who knows.

Yes, it did have water in it at one point.

 

When mine would die when hot after I first got it, I changed the ignition module & cleaned the fins of the heat sink, they were filled with grime. I got lucky cuz that solved it. As additional precaution, I fabricated an insulator of sheet alumina of appropriate dimension and disposed it between the heat sink and the cylinder head (or block, I can't remember which its mounted to without looking), the idea being to keep engine heat from dissipating through the sink, enabling the sink to more efficiently radiate heat only from the module itself.

 

Your test is great. The video is great. I get to change my distributor this week for the same reason as you. Thanks for your work and taking the time to post what you did.

 

Awesome diagnostic work. Just great. I like the idea of throwing it in the oven.

You can fix cars a lot better than many "professional mechanics" out there. I've seen a whole lot of them, it really is sad. They work on them all day and don't know nothing about them. Just how to turn a wrench.

I only claim to have half a clue.

 

Got my hands on a new distributor Thursday night. Installed it, put the water pump on, filled/bled the thing, and fired it up. Tested through two fan cycles, no codes, no issues. Went to bed at midnight.

Got up at 5 AM, got in the car and drove 580 miles to Vegas -evidence that I was pretty confident. Got to Vegas around 2, and then ran the car at the drag track there; ran a slew of 13.6's@103 and managed one 1.9 60' (best yet in this car) which got me a 13.5/103. So it was running...fantastic. Drove back home today. Put 1200 miles on it this weekend. Had the cruise set at 84 mph all the way to Vegas and all teh way back. Got 32.23 mpg going down and 27.11 coming back (AC on) for a 1200 mile average of 29.67 mpg. Not bad. Not bad at all.

The engine runs great, and also, the <2000 RPM high load miss problem that the car has had for years, is now gone. Pulls smooth from any RPM in any gear.

Thing is running great! Thanks to all who contributed to this thread!

 

Hey, you should have given us a heads up, we could have met you there.

Sounds like you had the problem figured out all along. Hopefully we will see you soon.....

 

 

Hey wayne! Sorry I didn't let you know about this trip. It came together really quick so no real notice. Plus I didn't know if I'd even be bringing my car until midnight the night before I left! No car would have meant no drag track.

I hope to see you soon one way or the other. Nikki Is in Park City today for a job interview...

 

Great info, thank you to all.
My '92 starts bucking when it gets heat soaked. I have replaced everything but the opti in hopes of solving the problem. (I used the "routine maintenance" excuse.) I only have about 90K on this opti. I guess I should not complain too much.