here is exactly what is going on. the car runs fine at all times idle,WOT,city driving, ect...except in overdrive at low rpms..1200-1600 if i lightly press the gas is starts busting up. sometimes pretty bad, sometimes you can barely notice.(doesnt matter engine temp).. it hasnt thrown a code yet. i first changed the plugs and plug wires with no luck. then i installed new o2 sensors. no luck there either. any suggestions?

 

How is your fuel system? Clean injectors? Clean fuel filter? Clean MAF?

 

Are you sure it is misfiring?
Have you checked it with a techII to see live misfire data?
Have you made any other recent changes to the car?

I agree with a possible fuel filter issue...

 

it has been a week and it still hasnt thrown a code. i havent done the fuel filter swap yet but i am tonight. as far as injectors, how would i go about cleaning? i think it may be a possibilty of MAF because earlier that day i cleaned and re oiled my k&n. i let it dry, went to the track 20 miles away, made one pass, left and drove another 50 miles around town. the misfire started as i was almost home from the trip. with that much driving with no issue until then i was doubtful of a bad MAF. now im not so sure. if it was fuel filter wouldnt i notice it at other rmps. once im over 1600 rpms in overdrive the "miss" clears up. i even took the valve covers off to check the rockers for lifter bleed off. everything seems fine. if its an injector clogged can a bottle of injector cleaner help, or should i remove them and inspect them? thanks...i did clean the maf..no luck

 

well, if you could use a techII to see what cylinder is misfiring, you could try moving injectors around to see if the misfire moves with it.

I wish you the best of luck with it, I just spent 2 weeks tracking down misfires in my car...techII said it was cyl. 5, but after wasting lots of time looking for it, it turned out to be a broken valve spring on cyl. 4....go figure.

Thanks
Mike

 

thanks. im checking more into the fuel now. i disconnected the fuel line to remove the injectors and fuel barely ran out. it is a 2001 corvette. ive researched that the most likely cause of this symptom is a faulty rear fuel feed pipe. There is a built in check valve (not replaceable separately). The rear fuel feed pipe is connected to the output of the left fuel tank, travels upwards and then "Y's" off with one branch going to the right fuel tank and the other branch going directly to the fuel filter. i reconnected the fuel line and primed the system again. im gonna go back out in 10 mins and see if the pressure bleeds off again. if its questionible then i will go get a pressure gauge to check. not sure if this would cause my drivibilty probs. but its a start. like i said i havnt noticed it being hard to crank or anything like that....

 

Had the same issue it was a plug/coil lead.

 

looks like its gonna be a fuel issue. i installed a gauge on the rail and im only getting 50 psi. then it goes to zero after the car sits for a little while. im gonna put the new filter/regulator on and see if that fixes it. if not guess the pump is on its way out.

 

well i replaced the fuel filter/regulator. it was definitly clogged up somewhat. when i installed and cranked the car again i was getting the full 58 psi. instead of the previous 50 psi. also the pressure is still bleeding off to 0 psi, but now it is taking an hour to do so instead of 15 mins. the car is still misfiring under low rpm load. i assume the pump may be bad, a bad injector, or possibly the check valve between the tanks...however i dont believe the bad check valve would cause the misfire/studder.

 

problem was fuel pump