OBD2 LT4 Corvette running horribly. It has a lack of power and feels sort of sluggish and hesitates under hard acceleration. Sometimes it will pull OK, others it wants to die altogether. No engine codes.

I pulled off the exhaust thinking that it was possible that there was an obstruction. I found the driver's side cat had been gutted. Honeycomb structure on passenger side cat appeared OK. Drove it around with the one cat and both rear O2 sensors removed, ran pretty much the same, eventually got codes P0140 and P0160 since rear O2's are not there. Also got P0410, found the air pump fuse is burned. OK, it's not the exhaust and I need to replace the air pump fuse and driver's side cat.

Looked in the factory manual to try to troubleshoot. Found on page 6-616 "Loss of diagnostic code memory. To check, disconnect MAP sensor and idle engine until the MIL <aka SES> comes ON. DTC P0107 should be stored and kept in memory when ignition is turned OFF. If not the PCM is faulty." When I unplugged the MAP sensor, it came off in pieces. Bought new MAP conector and MAP sensor and installed. Confirmed 5V at connector.

I unplugged the MAP sensor and let it idle for about 5 minutes, no code P0107. Then I drove it around with the MAP sensor unplugged. Ran the same, like crap. This time got the codes P0300 (random/multiple misfire) and the dashboard started flashing "SYS", but still no code P0107. I also did this same MAP test on my OBD1 Camaro, it immediately gave me the SES light.

Any other checks I should do before tossing this PCM into the firepit and buying a new one? The car has new plugs/wires/Optispark. Also just got heads redone. It seems to me that even if I had something else wrong, it should still give me the SES light with the MAP sensor disconnected. I also suspect the PCM because it has a sticker on it with a “SERV. NO.” I’m thinking this is a service PCM, maybe someone put the wrong thing in it?

 

Try tying the MAP sensor signal to either it's ground or it's reference voltage to see if the appropriate codes come up. Just leaving a signal hanging allows it to float.

Also, if you suspect the PCM is causing your engine to perform badly, it should show up in the real time data that it will show on the scanner. That is if you have an actual scanner and not just a code reader.

Third, if you suspect a defective PCM, places like auto value can put it on their programmer and not only reprogram it to the most updated software, it may show if the PCM has a fault as well. However notice I said MAY.