Let me start off by saying my 88 automatic vette has engine modifications and was running well with recent tuning. I decided before final tuning I would have a set of headers put on the car. I also had an MSD distributor cap and 8.5 mm wires put on. The headers were put on with all cats deleted. When I went to the garage that put the headers on the car started up, ran for a few minutes to hear the exhaust. The next day I went to pick up the car. The mechanic informed me that he had fired it up and left it run awhile to get it up to temperature burn off any debis in the exhaust. I started the car to take it home and noticed that the engine light would flash quickly and just as quickly go off. It was like the engine was going to quit and this is why the engine light would flash. I had to keep the rpm's up in order to keep the car from stalling. When i got home I checked for codes and there were none.

The following day I had checked all the spark plug wires and had not noticed that any were burnt or melted due to the headers. I also changed all the spark plugs since the ones in there were Bosch Platinum. I had changed to the AC Delco 41-629. With the change of the spark plugs, the car seemed to idle better. I ran the car around the block for a short 1/2 mile ride, the idle was noted to flash the engine light when in park and stall. It also did this with revving the car at higher rpm's. I would describe this as a hiccup or misfire. I tried to see if any codes showed at this time and a Code 51 Memcal appeared.

I had re flashed the bin file from the tuner and had him send me another file in case his file was corrupt. I tried the new file however it did not fix the problem.

My question is I know it is rare that PRom would be malfunctioning. Where do I go from here. What should I check? This problem is driving me nuts . I'm not sure where to look, how to diagnosis the problem and how to resolve. Any advice would be greatly appreciated.

 

Since yours is an 88 it may be different but according to the FSM for a 1990, a code 51 is a Mel-cal error.

It states:
Check that all pins are fully inserted in the socket and that MEM-CAL is properly latched.
If ok, replace MEM-CAl, clear memory, and recheck.
If code 51 reappears, replace ECM.

Not sure if that actually helps any....

 

Thanks mypatera. I had since cleared the code 51 by taking the negative off the battery for about 60 seconds. I started the car right up, it idled for about one minute and immediately without evidence that it was going to happened it stalled. It was like someone turned off the key but it wasnt turned off. I looked for a code and there wasnt any. Of course, it took a drive around the block the last time for a code to show. I had new injectors put on with my engine build about 10 months ago and as I said, it was running fine a week ago until the headers went on. This is when the problem started. Not sure where to find the PROM. Apparently, it is rare for the problem to occur here. I don't know if the ecm may be bad or not?

 

You may want to have a look at ECM grounds. Easy enough for them to get fubared when installing headers. There are about 6 of them attached to block, just below #7 exhaust port.

 

When the car wouldn't start, did you check whether it was a fuel delivery or spark issue?

 

Hind sight is 20/20 but those guys really should have disconnected the ECM before they started welding stuff.

You say your car will run for a minute or so before it acts like it wants to die. I bet the O2 sensor or wiring is or got damaged/shorted out when the headers got installed. The car will run in "open loop" ignoring the o2 sensor data until it warms up then once going into "closed loop" o2 data is critical to keeping the car running properly. Check the wiring going to the o2 sensor if you find no issues replace the o2 sensor. Or if the o2 sensor was reloacted further back in the exhaust when the headers whent on you may even consider a "heated" o2 sensor.

 

Thanks everyone for the replies I really appreciate it. I will try to get under the car in the next day or two to see if the grounds are in place. I will also take a cloase look at the O2sensor. I haven't found anything wrong with the spark plugs, each tube of the headers get hot. Does anyone feel this could be a problem with the ECM? How about the ignition module? I dont understand why it would start well, and it is almost like someone turned the key off when it stalls during idol.

 

i am having a similar issue with my 89. its not the o2, it would still run without one... i suspect a wiring (dizzy stuff or relay stuff) or im prob, havent had time to finish checking wires and even so, since it is intermittent its not fun....

 

Stormy, if you figure it out let me know. I had the ECM down last night I didn't see anything unusual, I made sure things were tight with the PROM. My Moates connection was wiggled around slightly. I made sure again that things were tight put an earlier bin file in the car. Car started right up and Idled for a good five minutes without any symptoms. I thought I had it licked that maybe something was loose. I put bin file 4 in (the latest file) started the car right up and into idle about two minutes it didn't stall as it had done in the past, it had the hiccups. THe engine light would quicly flash, the car would miss with the idle and tach going up and then back to normal until the next miss. Strangely enough unless it is just my imagination, it does seem slightly better that I manipulated things in the ECM. I'm doing my best to try to figure this out. Even with the several minutes of runnning last night,there are still no codes. I'm going to look to see if there was a ground wire missed. It was suggested that maybe the ignition module is bad? According to an earlier code that I did have and cleared, 51 was present (memcal error) which tells me to change the PROM or the ECM. I think all the suggestions thus far are potential links to what is going on but I just haven't found the exact one yet.

 

I have only seen a couple of computers go bad, ever... if the car will run then its unlikely the computer failed. U may have sone bad solder joints in urs tho.

 

OK guys have an update. I took the car for a ride after I looked around underneath to make sure all the connections were grounded. The car threw a code 42. With some good advice from Pete K, I ordered another iginition module. The old module was taken and tested. I was told the old module was "good." At this point I wasn't sure if this was my problem or not. Again, good advice from Pete K. I was told that the tests are not always accurate. I changed the module and my symptoms diappeared. So for those of you who have similar problems, this may be the answer. The ignition module doesnt need to leave you in a situation where the car won't start to be the problem. Again, thanks Pete K. for your diagnosis of my problem. Now, on to put a heated oxygen sensor into my long tubes so I can get some accurate data logs.