mckinpe21

Hi, Looking for some ideas where to search now. My 92 LT1 6sp has been running really well until recently. The symptoms I have which have indicated a limp home condition according to the FSM is: Start car, within 3 -4 secs, Service engine soon light goes on, Both fans begin to run. I followed the FSM and it looks as if the book is saying its the ECM. I have an OB1-scanner, does not pulls up no codes after startup. C-12, H36 every time I use the paper clip technique.

When driven other than the light and fans, car runs strong, no diminished performance

Any other ideas to test or check?

I went through each of the sensors. Battery looks to have a good voltage. Although from my past searches some have notes that using a battery tender sometimes causes problems. Not sure if that is true?

Opti, wires, injectors all new.

Any help is greatly appreciated

theadmiral94

Two quick thoughts.

1. Coolant temp sensor in water pump bad or disconnected -- check what the digitial dash coolant temp says..

2. bad ground connection -- especially the one at/near the battery ground cable connection (i.e. driver side bell housing).

mckinpe21

Thanks,

I did disconnect and start and no change. This gauge is reading properly, Many years ago this sensor was off the charts and I remember it affecting the idle and general drivability.

I'll check that ground, thanks, I'm thinking of taking battery out and getting it checked. The volts check out but I think I need to start ruling stuff out.

jaa1992

Did you short the ADL pins to have the codes displayed by module on the dash?

Got a FSM handy? The procedure is there to pull the CCM, ECM and other module codes.

mckinpe21

Yes, that is the strangest part, Whatever is happening is not triggering a fault code the next time the car is started.

So Start car, within 3 secs light goes on, both fans stay on. Shut down car, Short the ADL, and the I see C12, H 36, or running normal

And yes I have the FSM, and while following that it leads me to trying a faulty ECM, not sure which page that was in the second book.

jaa1992

Yeeccchhhh
Where do you live?
Start looking for another ECM - they are scarce as hens teeth.
Over at the guru there was a guy that had good results with RockAuto's rebuild service.

I keep a second ECM around for just those places in the FSM that say "ECM"

amlarson2001

I know this is an old thread but this is literally the same problem I'm having. Just wondering if you can shed some light on what fixed your car. Thanks

Nomake Wan

I would assume it's the ECM. The ECM on these older cars is somewhat notorious for having cold solder joint breaks and/or bad capacitors. There is a very well-respected rebuilder for these ECMs known as SIA Electronics who can repair it for you. The only thing to make sure of is when you get it back, be absolutely sure the MEMCAL is fully seated in its slot. It can come loose during shipping and will cause all kinds of fun problems if you try to start the car with it like that.

Heck, just for fun, open the access panel on your ECM and make sure the MEMCAL is fully seated in its slot. If it's not that can also cause limp mode issues. But yeah, chances are you're looking at an ECM repair.

Peter McKinley

Hi, yes this was my thread from 2012. From my recall I determined the Optispark while functional was starting to show signs of breakdown. This was my second optispark and like many of us it was a faulty Ebay Delco unit. I bit the bullet and bought a third Delco from Summit with an understanding it was a remanufactured Delco but Summit at least offered a year warranty.

That fixed the problem. I also retrofited a MSD cap and vented it. Worked great until I sold the car in 2017. Great car.

But as many have said the ECM was a 1992 only model which is a nightmare if you had to replace or service.

amlarson2001

Really apricate the reply. I think im also going to replace the (according to the guy I bought it from) new opti. Thanks