Help !!! 92 GA stalls when hot

[mitch]

My '92 3.3L GA quits running when engine is fully hot (after about 15 minutes, coincidentally, just at the same point when the cooling fan kicks in). It also stalls with the cooling fan unplugged at around the same point (15 minutes). It doesn't matter if the car is driving or at idle, it completely dies just as if I turned off the ignition with the key.
Then it won't start again for a few hours until things cool down. I changed coil pack/ignition module and computer before I discovered the connection to the car being warmed up to a certain point. Ground & powere wires were wirebrushed. The computer is not throwing any codes. The AC compressor is bypassed on the serpentine belt. The temperature guage is reading correctly and triggering the cooling fan at the correct point so I'm sure the CTS sensor is OK. I'm at a loss as to how to proceed here .... does anyone know offhand what could be the problem here ???? I'm goinf to check for spark after stall tonight but any other clues would be helpful.

[SlamedAM]

Losing any coolant? :/ Mine did the same thing, except mine was losing coolant and sucking all the coolant into the oil system because of a blown head gasket. What a PITA to repair!

[rixGAphx]

My *guess* is the PCM is operating the engine just fine in warm-up 'open-loop' mode, then the PCM is shutting down on (or more) major systems when it switches to 'closed-loop' at a certain temperature.

If this is the case, try disconnecting the temperature sensor before you drive-off this evening.
This should keep the PCM permanently in 'open-loop', so you'll never stall.

Try this as a diagnostic.

You may have a faulty PCM, or a disconnected/failed sensor the the PCM thinks is SO wrong that it's not safe to run the engine (like low oil pressure).
I dunno enough about the 3.3's to be of much more help.

That car must have 150K miles??
Has the O2 sensor or the cat ever been changed? Those parts are expected to fail, so it wouldn't hurt to change them (well, it hurts the wallet :roll2: ).

Good luck.
-Rick

[mitch]

Catalytic converter was changed a few months ago.
O2 sensor I don't know...I just got the car a year ago but my understanding is that when O2 sensor is bad the car just idles/runs badly because the mixture is corrupted. This is not the case here ... the car runs fine then just dies when hot. If it was a blown head gasket what are the other symptoms ??? Can you see discoloration in Oil dipstick ??? I'll check that tonight. The computer doesn't flag any codes in this problem... It's weird because if a sensor was not being seen or intermittant the appropriate error code should be raised.
Here's my next big question... can the removable PROM inside of the computer go bad ??? because I had to swap in my previous PROM from my former ECM to the new one because the new computer was from a Buick not a grand AM.

[mitch]

Did your car experience major overheating during this warm up period or did it just reach the expected 1/4 temperature on the guage and then stall ? Because in my case, everything seems normal... the guage hits 1/4 temperature and stabilizes a bit lower when the thermostat kicks in... its only about 5 minutes later when the cooling fan normally kicks on that the car shuts down. But the problem has nothing to do with the fan because it stalls whether the fan is plugged or unplugged.

[rixGAphx]

It is doubtful that it's a blown head gasket.
The usual symptoms for such are much different.
And, the engine *generally* runs well enough to get to a mechanic (unless there's coolant in the oil).

There are several ways a head gasket can 'blow', with different symptoms:
* From cylinder direct to outside: Rough running, no other effects.
* From cylinder to water passage: Rough running, excessive water vapor in exhaust, loss of coolant level, possibly foamy coolant (from exhaust), possibly wet spark plug, possible hydrolock. Oil generally fine.
* From cylinder to oil passage (very rare): Rough running, excessive air pressure in crankcase, possibly oily spark plugs.
* From water passage to oil passage: Runs fine; usually a 'chocolate milk shake' appearance to oil on dipstick, possible oily scum in coolant, loss of coolant level.
* From water passage to inside of 'V': Runs fine; usually a 'chocolate milk shake' appearance to oil on dipstick, possible oily scum in coolant, loss of coolant level.
A compression check of the cylinders will reveal the first three conditions above.
A pressure check of the coolin system *may* reveal the fourth and fifth conditions.
Since the head and block expand at different rates as they warm, a leak may be present only when warming, only when hot, or only as it's cooling down.

IMO, don't worry about that now (unless there's a 'chocolate milk shake' where you used to have normal crankcase oil) since your symptoms are definitely a control issue.

* * * *
When the O2 sensor starts to fail, it gives poor readings to the ECM which does, indeed, cause rough running.
When it fails, the ECM will store a code AND revert to 'open-loop', where the running becomes smooth but the exhaust is rich and pollutive.

* * * *
Easiest way to screw up ANY GA is fart with the electricals.

You changed ECM's with a non-GA ECM and reinstalled a GA part.
And you wonder why the damned thing won't run right????

Not to put too fine a point on it, but you're screwed.

I'd like to see you back on the road, and I'd like to help.
But I just don't have time to waste on this bone-headed self-created control problem.

My best advice is find an EXACT replacement ECM (try E-Bay) and return your car to a stock 'normal' GA configuration.

Good luck.
-Rick

[mitch]

The scrapyard considers one 3.3L same as any other except for this PROM module so they told me I absolutely had to swap in my old Grand-AM PROM (which I did) when they sold me the used (supposedly OK) ECM. I got the car running OK only by swapping in the non-Grand AM PROM (because I had the one that came with the scrapper ECM).
It was my last resort before limping on over to dealer to get my pockets raped !!!

Thanks for all your feedback !!!