Good afternoon C4 Tech,
I place a problem with my 1990 base corvette in the wrong column. (New at this) Lets start by telling you about my car. I was bought last July with 53000 miles: 9/14 - 45000 miles, new injectors, fuel pump, 160 thermostat, aftermarket prom chip (93 octane)
11/16 - 48700 miles new plugs, new battery. 12/16 - 49000 miles, rebuilt HP trans with 2500 stall converter, 3:73 gears. the car ran great last July when bought (7/20); 5/21 on my way home from work the gas gage (range) said 64 miles left, the car started to run like crap ( no acceleration)
so i thought the gas gage was off. stop for gas, after a mile or so i could not step on the gas ,it would bog badly and shut off. started it and ran like crap . would not go at all. ( hard starting) called for a flat bed and sent it home. After dropping off the car it started right up and had no problems for a month. then it did it again. 6/21 - 57000 miles changed fuel pump and it ran great for one day, since that day i changed fuel reg (stock) fuel filter, map and tps sensor (set tps to .54 vdc) plugs wires, plugs( came out black) cap, rotor.O2 sensor. Stall have major bog.
place pressure gage 37 psi steady at idle, 41-43 when trying to raise rpms. placed my scanner on the car NO CODES. when shut off no fuel pressure drop. PEASE HELP

 

The one thing I would suggest you check is the Coolant Temperature Sensor to make sure it is giving the right information. There is a chart in the FSM that gives you Resistance Value to Temperatures conversion chart.

The reason you want to check this part is that it has major input on the fueling of the Corvette. If the CTS is showing that it is colder than it really is then the engine would get extra fuel like an old Carburetor's Choke would do. It would make the fuel mixture richer based on how cold it thinks it is. This might explain your black spark plugs you mentioned. Likewise if the CTS is telling the engine it is already warmed up then it would have a harder time starting when cold.

The CTS is involved in a lot of the Fueling decisions made by the ECM. If it is bad it could cause issues like what you are experiencing. On my 1988 C4 the CTS is on the front of the Plenum and it uses three wires. They are easy to find and verify their operation with a Multi-meter. The CTS is one of the three primary sensors your engine uses and it is important to have it working properly.

If you need the Chart to convert the resistance Value I could post it for you. It is on this forum a few places I would guess.

Is it possible that your fuel pump is picking up air?

 

All of those parts were likely due to be replaced anyway. They're routine maintenance parts, for the most part.

Agree with the previous advice about checking the coolant temp sensor. Particularly given the aftermarket chip.

Good luck with it.

 

If the coolant temp sensor doesn't help, I'd put the stock chip back in