1990 L98 engine has been rebuilt, all sensors have been replaced, new plugs, wires distrubter, everything is new, grounds have been checked and rechecked, no vacuum leaks, proper fuel pressure and does not bleed off, PROBLEM: take the car out to drive step on the gas runs like it should, next time step on the gas, car falls on its face, no codes or check engine light, only thing i havent replaced yet is the stock computer chip and that is next on the list ...... any ideas would be a great help, also this car is made up from the factory with 89-90-91 parts.

thanks
gary

 

Hmm there are a few different things that come to mind. What exactly do you mean by 'falling on its face?'

Have you driven around with a fuel pressure gauge attached when this happens? Still have good readings? Other things im thinking about are ignition module or maybe knock sensor... maybe others can chime in.

 

i have replaced all sensors from top to bottom,side to side and front to back, there is nothing left to replace, 2 new coils, rebuild distribtor then replaced with new one 2 sets of new plugs, new plug wires have placed fuel pressure gauge on fuel rail and have great fuel pressure at speed and idle, timing is set as called for in the 1990 corvette service manual, grounds have been checked and rechecked, fuel filter replaced, as stated before the only thing left to replace is the computer chip and that will be done soon, When driving the car, when you step on the gas it will accelerate as should, but the next time you step on the gas the car will bog down, not accelerate, if you back off the gas and then ease into it very slowly you can sometimes get past that point. this happens between 2500 and 3000 rpm, have looked in the corvette manual under stumbling , have done everything there to no end...no work. have looked at GM site dl all there information and it seems that the 1990 year corvette is nothing but a pain in the butt. they have a mulitude of electrical problems some of which i have run across but nothing about the problem i am having. have taken car to local chev dealer, put on scanner, shows no codes or problems, have been there so many times they now tell me dont bring the car back we dont want to work on it, cant help you

gary

 

Is the MAF rebuilt or new? Tap on it while the engine is running and see if engine stumbles. Went through several rebuilts, finally bought a new A/C Delco one to the tune of almost $400.00, the Vette one is diff from the Camaro ones (Gee, I wonder why?). [8D]

 

Also, take some carb spray and spray around intake area, plenum, injectors while engine is running to check for vacuum leaks. Have you watch O2 sensor reading on a warmed engine around 2000 rpms? Is it active or does the voltage stay low, < .2 volt?

 

mech. is right on about the vacum leaks. that's what i was thinking, but you didn't say if you check out the thottle pos. sensor?

 

no vacuum leaks, tpi replaced and set, no maf on this car, waiting on new computer chip for car now

 

Next thing to check is the fuel trim or intergrator. For that u would need a scan tool. Fuel trim is in % and intergrator is in numbers. Normal intergrator number is 128, more it is trying to fatten it up, less it is trying to lean it down.

 

After that, next thing would be to start with a lab scope and check injector pulse rate, which you can check with scan tool also. Pulse rate usually runs around 2 to 4 milliseconds at idle and increases with throttle. Also check voltage patterns on MAP sensor. Your problem is either a timing issue or lean misfire. If you had someone who really know what they are doing and has a labscope, they would be able to run down the problem. Wish I had better news for you.