Nayr

Hi. I am a little stumped on my current issue. Within the last few weeks my engine will shut off (abruptly, no sputtering) usually when it gets up to ~220oF but has done it when it is ~180oF. The engine has stalled while moving and while at a stop, only idiling and being driven. The check engine light does not come on when it stalls, unlike what it did about a year ago when the Opti went bad and the engine light would come on. I then have to wait 5-10 minutes before I can start up the car again. Afterwards It will drive fine for awhile and I have had it sit idling in the driveway for over an hour with no problem (other times it will stall after 10-15 min)

I thought it could be a heat issue with the ICM so I replaced it and moved the bracket off the head to reduce the amount of heat going to the ICM. Thought it fixed the issue but then a week later it stalled again. (I only drive ~15-20 min each way every day).

I then purchased a Actron 9185 scanner (in the 9190 kit) and scanned for codes. No codes were present. Which left me confused. I then did a running test and waited for the engine to stall, when it did it said no codes present, however, after some continued testing I was able to get 5 codes 79, 81, 82, 83, and 86.

79-83 I found but 86 is not on the list. The scanner says it is "Low ratio error calculated ratio different from actual".

As for 79 the trans temp was ~140 when it stalled (other times it stalls these codes do not pop up). 83 is for manual so I do not know why that is here. (Yes i did correctly input my car info into the scanner)

A strange thing did occur though when it stalled. The PCM disconnected from teh scanner and when trying to reconnect it would connect for a few seconds then disconnect then I would connect again (It did this several times before staying connected). This makes me believe it could be the PCM going bad (Same with the weird codes and only sometimes showing them)? Also the scanner will show no codes present but after running for a little bit it will change back forth from yes/NO, but no codes are being stored.

Additionally, when starting the engine sometimes it fires right up, but it sometimes has to turn over for a second before starting and then it has a fast but incremental startup as if it is not getting enough combustion. (I can hear the Gas pump pressure the system too when I turn the key, even after a stall)

Thank you, and I will take any suggestions

Skedaddle

83 has two definitions:

Reverse inhibit system (manual transmission)

TCC PWM Solenoid Circuit Fault (automatic transmission)

Use Shoebox's LT1-specific code list. The definitions given by the scanners tend to be generic. DTC 86 is not on his list, not on the list of DTC's in the 1994 factory shop manual. Would appear to be a quirk of the scanner (not unusual).

http://shbox.com/1/Dtcs.htm

None of those faults shuts down the engine.

Sounds like an intermittent power supply to the PCM. Can't rule out a problem with the PCM, but PCM failures are extremely rare.

Might want to scan the PCM using Scan9495.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Nayr

Thank you may have to look into that. Otherwise, it stalls at different temperatures and I can get it to idle in the 230 range (when I step on the accelerator for a bit) and it will not stall. So i guess it could be an intermittent opti issue without throwing any codes.

Any other ideas?

Injuneer

Typical Opti heat soak problem is with the optical cam position sensor. Even an intermittent problem should set DTC 16 and 36. An intermittent power supply to the PCM may be causing the codes to clear.

sleepyguy24

would the intermittent power supply to the pcm be related to the optispark?

Injuneer

The PCM receives power, both switched and unswitched (for the volatile memory) from the battery, through fuses - conventional on the switched, fusible links on the unswitched. The Opti has nothing to do with supplying power to the PCM. It's actually the other way around. The PCM supplies 12 volts to the Opti for the optical cam position sensor, and 5 volt reference for the pulse signals the Opti sends to the PCM.

There are two PCM grounds that can upset power to the Opti. One is at a stud on the block near the starter, and the other is at one of the studs that holds the ICM/coil bracket to the driver side head.

4th Gen LT1 F-body Tech Articles

sleepyguy24

awesome I appreciate the info.have a 94 lt1 Firebird with A4. Having good startup but once the engine is warm, the battery voltage comes down between 10.5- 11volts. Think it might be a ground problem. I will check those two ground points you mentioned. Could be the ground near the starer. Also I have partially broke off the alternator bolt holder on the upper right; closest to the engine. Would that point serve as a ground for the alternator? If so will the broken piece be an issue?

Picture of engine bay. (94’ Firebird formula A4, LT1) might be able to see where I broke off a piece on the accessory bracket where the alternator bolts into; it is to the right side of the alternator.

Injuneer

Where are you reading the 10,5-11 volts?

You can read the voltage the PCM sees with a scanner, or free software like Scan9495. That could be affected by the grounds I mentioned.