93 Corvette Plagued With Problems! HELP!!

C4Jalopy said:

Hi,
I have a 1993 Corvette with the ZF6 transmission. I have tried so many different solutions to try and fix this problem and none seem to work. Let me tell you what is going on and then what I have done.

The problem is that after the engine gets warm, the car will randomly stall out and die. This could be 2 miles or 20 miles. I don't lose power to electronics but the AC turns to heat and the power steering fails. The engine will still move when Im at a high speed but once I come to a stop its kaput. I also currently have a code 15 on the dash which is causing an SES light. The digital display reads 142 degrees constantly. At one point it did work correctly but now it does not. I also have a 27 code that will not go away for EGR solenoid. Sometimes a code 62 will popup in section 9 as well. I have also seen a code 72 and 74 in section 1 but only one time after it stalled. This car is a mystery!

Now as of what I've tried,

Tested fuel pressure, changed fuel filter, fuel sock etc.. (It is getting plenty of fuel)

I have gone around and tightened/cleaned every ground in the car.

I have cleaned and inspected both sets of Maxi fuses near the battery, they are fine.

I have replaced the EGR solenoid and valve since the valve was sticking and hard to move. No change to 27 code still runs like crap.

I have replaced the CTS on the water pump and made sure to test using the FSM flow chart to make sure it was getting correct signal and it seems to be fine. (This did not show back up for awhile but now it is preventing the car from running correctly)

All of the vacuum hoses seem to be OK.

I removed the ECM and sprayed contact cleaner on the connectors and made sure they were in good condition.

I opened the ECM and the inside is immaculate but i went ahead and blew it out and reseated the chip anyways and cleaned with contact cleaner. (The ECM board itself looks OK but im still concerned that the bubbly looking traces on the ECM could be a problem. The whole back of the board is all bubbled up on the traces and solder points)

I cleaned the MAP sensor which smelled like gas but was getting correct power as far as I am aware

I checked the ICM which had ZERO thermal compound on it, so I tried to use thermal compound on mine to no avail. Replaced the ICM just now and I am still having problems.

Currently the car will start fine and then 20 seconds later it will turn on the SES light and show a code 15 in section 4. The code will then go away after around 10 seconds but the engine will run like absolute garbage until the SES code comes back. Funny how it runs worse with the code off vs on. It will continue to cycle like this forever. Both coolant fans kick on immediately after SES light is thrown

Im not really sure what to do at this point. I haven't looked at the Optispark yet but that might be next... not sure how that could affect CTS and EGR but maybe something else is wrong. In the meantime I am going to continue to check wiring to see if there is a short in the wiring harness somewhere or something blindingly obvious that I am missing. ANY suggestions would be helpful if you guys could point me in the right direction!!!

Thanks,
Joe

Click to expand...

moodman said:

Have you found the issue yet?

Click to expand...

C4Jalopy said:

Hi,
I have a 1993 Corvette with the ZF6 transmission. I have tried so many different solutions to try and fix this problem and none seem to work. Let me tell you what is going on and then what I have done.

The problem is that after the engine gets warm, the car will randomly stall out and die. This could be 2 miles or 20 miles. I don't lose power to electronics but the AC turns to heat and the power steering fails. The engine will still move when Im at a high speed but once I come to a stop its kaput. I also currently have a code 15 on the dash which is causing an SES light. The digital display reads 142 degrees constantly. At one point it did work correctly but now it does not. I also have a 27 code that will not go away for EGR solenoid. Sometimes a code 62 will popup in section 9 as well. I have also seen a code 72 and 74 in section 1 but only one time after it stalled. This car is a mystery!

Now as of what I've tried,

Tested fuel pressure, changed fuel filter, fuel sock etc.. (It is getting plenty of fuel)

I have gone around and tightened/cleaned every ground in the car.

I have cleaned and inspected both sets of Maxi fuses near the battery, they are fine.

I have replaced the EGR solenoid and valve since the valve was sticking and hard to move. No change to 27 code still runs like crap.

I have replaced the CTS on the water pump and made sure to test using the FSM flow chart to make sure it was getting correct signal and it seems to be fine. (This did not show back up for awhile but now it is preventing the car from running correctly)

All of the vacuum hoses seem to be OK.

I removed the ECM and sprayed contact cleaner on the connectors and made sure they were in good condition.

I opened the ECM and the inside is immaculate but i went ahead and blew it out and reseated the chip anyways and cleaned with contact cleaner. (The ECM board itself looks OK but im still concerned that the bubbly looking traces on the ECM could be a problem. The whole back of the board is all bubbled up on the traces and solder points)

I cleaned the MAP sensor which smelled like gas but was getting correct power as far as I am aware

I checked the ICM which had ZERO thermal compound on it, so I tried to use thermal compound on mine to no avail. Replaced the ICM just now and I am still having problems.

Currently the car will start fine and then 20 seconds later it will turn on the SES light and show a code 15 in section 4. The code will then go away after around 10 seconds but the engine will run like absolute garbage until the SES code comes back. Funny how it runs worse with the code off vs on. It will continue to cycle like this forever. Both coolant fans kick on immediately after SES light is thrown

Im not really sure what to do at this point. I haven't looked at the Optispark yet but that might be next... not sure how that could affect CTS and EGR but maybe something else is wrong. In the meantime I am going to continue to check wiring to see if there is a short in the wiring harness somewhere or something blindingly obvious that I am missing. ANY suggestions would be helpful if you guys could point me in the right direction!!!

Thanks,
Joe

Click to expand...

C4Jalopy said:

I cleaned the MAP sensor which smelled like gas but was getting correct power as far as I am aware

Click to expand...

autowiz said:

Did you know the MAP sensor has a diaphram in it akin to a diaphram that you'd find in a fuel pressure regulator or an vacuum relay or actuator? I mean a much smaller and different looking flavor but that sensor is now 30 years old. What do you think the odds are of that sensor's internals still being soft and pliable to the point of sending back exact calibrated data to the tenth or hundredth of a volt?

And yet the MAP sensor is primarily responsible for fueling in your car.

Smells like gas sounds like too much fuel.

One possibility of what you are describing is a decades old failed MAP and a controller that can't run an engine from it and when it realizes this and codes for the problem it can run better in limp mode.

REPLACE the MAP and RETEST and REPORT back

Click to expand...

moodman said:

You hit on an important issue, and one I think most don't know. Although you responded to C4Jalopy, I wanted you to know that I have sent my ECM back to the original rebuilder (because they have a warranty on their work) and when I get it back I intend to also replace the MAP sensor. I will let everyone know the results. But in another thread which you helped me track things down, I also got some advice from someone really familiar with the C4, and he said that almost certainly my problems are coming from the ECM, not the Optispark. But your advice about the MAP sensor is a very important piece of advice. Thank you.

Click to expand...