Hi from EU

Our customer (we are garage) brings here C4 corvette which is totally unknown car here in Europe. Few shops tried to sort this car but without luck so he brings it here as last chance for repair.
As vin decoder said is C4 1991 with L98 engine

Car had 2 major problems.

1.) it sometimes died without any reason
2.) it runs heavy heavy rich causing non starting and all **** comming with it... (but strange is, sometimes it can run normally with AFR 13-14)....then after 10 minutes its AFR 10....

After few hours of diagnostic I found that first problem with "cutting off" engine is ECU PCB. 30+ years for this ECU mounted under hood....bad.
As you touch PCB of ECM it does everything......(clicking sound from engine compartment). I found some cracked joints near MCU on PCB and we "resolder" whole PCB. + "eeprom" memory was little out of slot.

Now car start and runs without cutting off, you can touch and move ECU itself as you can, it has no effect.

But running rich is still here.... it runs AFR 10 after start and holding still...

Any advices? possibly ECU DEAD?
I am going to measure all analog values comming to-and from ECU with oscilo at monday, look at fuel injector pattern, temp sensors, map sensor ....etc.
Also I ordered OBD1 ALDL cable from ebay + tunerpro to see some live data from ECU...beucause without data I dont know what is happening.
But as I said, in EU this car is totally unknown and I can miss some important points!!!!

Thanks!

 

It should be throwing some codes-is the check engine light on? Once you can scan live data I'm sure the problem will jump out at you. I would suspect the O2 sensors, however live data will show the problem.
Congrats on the ECM resolder!

 

do the 91s have the same FPR set up as other L98s? when the diaphragm cracks, it lets excess fuel into the intake.

 

Very good point/possibility also, yes 1991 is still the same fuel pressure regulator.

 

Thanks, how good accesible is that FPR? I will check it for fuel leaks....

It will take weeks to ALDL cable to arrive from USA here to EU so...I wil work on that car in "blind" mode....
so monday plan is:

check FPR for leaks
check ECU injection pattern for injectors..how long is activating injectors and if there is no full ground....means ecu is holding injectors activated still.... ( I have strange feeling)....

 

The FPR is at the back of the fuel rail-pull the vacuum line off it and see if there is fuel in the vacuum line.

 

Where in EU are you based? I am in Czech and here I found few C4 skilled guys to help me with my 85 z51…

 

Where are you from EU ?

 

SK...

but I think we will solve it ...

I suspect ECU..maybe it has more damage that we repair