skyhawk50

Just as the title says, my 92 LT1 starts, runs great, then suddenly shuts off at 204 degrees. So far I've replaced the ICM, Coil and CTS. Car runs smoothy, then abruptly shuts off. I've searched the threads and am wondering what the next step would be. Opti was replaced about 3 years ago ( SacCity) Do most opti issues involve a rough run condition prior to their failure? Seems strange that it always shuts off within a degree or 2 of 204. Thanks in advance for any input.

Additionally, after about 10-15 minutes, temp drops to 175-185, it starts right up,

billschroeder5842

I'm not sure, but does the LT1 have a shut down provision for high temperature? Think of a rev limiter for high RPMS?

If so, you engine thinks it is over heating. If not, I'd still be looking into your coolant sensor system as this sounds more electrical than fuel or temp related.

BTW... how do you know it is precisely 205? Are you using a thermo gun or do you have a digital gauge? The factory dash gauges are all over the place and can give you false readings.

LT1_383

Before replacing anything else, do some testing. When it shuts off, verify that you still have spark. If it still has spark, check injector pulses to make sure they are threre. Finally, make sure you have fuel pressure when this is happening.

c4cruiser

My old '92 never had an issue like that and I had seen temps as high as 215 or so. The LT1 did have a fuel cut off built into the ECM when the engine reached 5850 RPM, but it didn't shut the engine down, it just reduced fuel flow. Once the RPM dropped below that value, the engine would run fine again.

Are you seeing that temp reading from the digital display? That would be much more accurate than the analog gauge. The analog gauges are not linear and not always accurate. A bad coolant temp sensor may be the cause, but you may need a scan tool to verify that. Isn't there separate sensors for temp reading? One goes to the ECM, another for the gauges?

205 degrees (Fahrenheit) is not really "hot" for an LT1. In fact it's well within the normal operating temp range. Besides checking for spark, get a fuel pressure gauge to check pressures when driving and when the engine starts to run rough and die. If you have an AutoZone store near you, you can "rent" a gauge for free. You put a deposit down on the gauge and when you bring it back, you get your deposit back.

Once the gauge is connected, place it on the windshield so you can see the face and tape it in place with duct tape.

skyhawk50

Digital temp - only using this # for a baseline.

skyhawk50

I'll give this a shot when a helper gets from work>

skyhawk50

Have a gauge. Will give it a shot

JackDidley

Wildass guess, short circuit in the cooling fan. Happened to me once. Fan motor was bad. As soon as the fan kicked on, the car had a bad miss. One day that fan motor went up in flames.

antfarmer2

Get a noid light you can check them by yourself. Free at part store. Look at your temp sensor on your pump. You did use the right thermal grease on you ICM?

Tom400CFI

Fan doesn't turn on at 204, so not likely a fan.

I agree with the above about spark...when it dies you have to confirm if you have spark or not.

It could be the opti; mine died with heat (right around 208*F)....

See diagnosis, HERE




.

skyhawk50

latest update: ran the car in the driveway this afternoon. digital temp gauge went up to 200, didn't shut off. Cooling fan kicked on, temp dropped back down. Got real brave and went around the block...no issues. Pulled into driveway shut it off...started right up. Let it run for about 20 min, no problems. ???? For now, it's good.

thanks for the input.

skyhawk50

[QUOTE=Tom400CFI;1594256610]Fan doesn't turn on at 204, so not likely a fan.

I agree with the above about spark...when it dies you have to confirm if you have spark or not.

It could be the opti; mine died with heat (right around 208*F)....

See diagnosis, HERE




Nice video !

pcolt94

I agree with this also. Really need to check fuel pressure (as far out in left field as it seems) just to make sure it's there so you don’t go off in the wrong direction.

On the 92s the ECM have given problems with heat. If the fuel pressure is good when it dies and the system pressurizes with the 2 second prime by cycling the key to ON, checking the injector pulses is the next step. If there is no injector pulses, the ECM could be the problem.

Also, if there is spark (and no injector pulses), you can almost eliminate the opti because you cannot have spark if there is no pulses from the opti.

JimLentz

If you are having ECM issues you usually get codes. My 92 ECM had cold solder joints and had some strange symptoms that changed over time. The odd thing for me is I drove it home 240 miles when I purchased it with no issues, but a couple of weeks later had on and off problems. Mine did not seem to be temperature related as once it started for 2 seconds and then shut off and the engine was cold.

geb@abq

Did you do anything to the car ? Add any parts, make any adjustments ?? Did it cure itself ??

skyhawk50

I had a return of the problem. Drove it approx. 20 miles, no problems. Digital temp climbed too 220, fans kicked on, temp dropped to 217, so far so good. Parked, went in a store for about 1/2 hour, NO START ??? Waited additional 10 min, started right up. When it's running, it's smooth as silk. No rough running at al. NO codes being thrown. ( I got the paper clip method down pat )

WVZR-1

With an "under-hood" ECM I've seen people actually ICE DOWN an ECM when it quit at higher temps. I've never done it myself but for the '92 - '93 LT1 I'm quite sure a friend has done it more than once.

The 10 minute "cool-down" and then crank/run seems to hint a MAYBE!! Carry a small cooler with an ice-pack or FREEZE PACK and go for another ride!!! LOL

Tom400CFI

Or just open the hood. That will cool the ECM pretty quickly, but not the Opti.

geb@abq

Sorry...guess I missed something: "I HAD A RETURN OF THE PROBLEM" led me to believe that you had changed something. I just got back for Autozone, and had 2 ICM's checked, and both failed. Bought one of theirs for $85 & had them test the new one before I left. This is the 4th ICM: the original OEM, one POS I got from A1 Auto, would not even start, and a new DELPHI that showed "fail". I have been chasing a "lope" for about a year, throwing parts at it, and biggest problem has been bad parts. I think I have finally decided that it was a bad ICM from the start. That is after having replaced opti, plugs and wires, coolant temp sensor, oil pressure sender, o2's, fuel pump, etc. Last "failed" ICM (the new DELPHI), if the car didn't start with first few revolutions, then would not start, would backfire, and fart but not start. Let it sit for a few minutes, and start beautifully.

Have you replaced any parts ?

skyhawk50

Yep, still having issues. Went out this AM, car would not start. Approx 3 hours later it started, pulled into garage, shut it off. Would not restart. Checked fuel pressure......no issues. Checked voltage at ECM to opti harness A- 5 volts +-, B - 5 vots +-, C- 10.8 volts. Evidently the ECM is sending the proper juice to the opti. NOID light on injector connector did NOT light. Can I assume that a dead opti will cause a NO START situation. Prior to this the car ran great cold but had no start issues when Hot.