Tyler Z28

iTrader: (1)

the car is a 1999 z28 102K miles LS6 intake 85mm TB Long tubes ORY stall and gears and its tuned, i have already replace the fuel pump, plugs, o2's pcv valve and pcv hoses, the problem with the misfire only comes on when im on the freeway or going 65+mph in town and it will stay on or go off and on while im driving, i took it to my tuner today and he looked up the mis fire count and on 2,3,4,7 they were all about 3000-7000(when i took the car on a few roadtrips the SES light was blinking the whole way there and back so that might be why the count is so high) and the other 4 cylinders were in the 100's he said that my stock injectors were going out and i should replace them along with the wires. does this sound right? and does anyone have any other ideas? thanks

lt1pwr1

iTrader: (1)

What brand o2's did you use in the replacement? I HIGHLY doubt you have injector problems. Flashing SES is a hard misfire so possibly wires. Make sure they are snapped on the coils and plugs good first.

Tyler Z28

iTrader: (1)

i cant remember but i think they might have been bosch o2's and the plug wire are on there way and should be here next week, and i spoke with my tuner again and he said the fuel trims weren't right also, could that still be from the plug wires?

Tyler Z28

iTrader: (1)

UPDATE: i checked the resistance on all the injectors and they were all at 15ohms which is with in spec, im going to check the plug wires and coils with a spark plug tester in a little bit.

lt1pwr1

iTrader: (1)

Well, first of all it seems everybody has bad luck with Bosch o2's. I wouldn't put them in any car of mine. I would stick with Denso.

Fuel trims that are off won't be caused by bad plug wires. Fuel trim issues could be because of the Bosch o2's (wouldn't surprise me) but which way are they trimming? Is it adding fuel or taking fuel away? You may have bad intake gaskets making the car run lean. On a cold engine, you can try spraying carb cleaner around the intake where it seals to the heads and see if the idle changes. If it does, you need to replace the intake gaskets.

Lastly, could be tuner error....is this guy reputable? And did these misfires happen right after you had the car tuned?

Tyler Z28

iTrader: (1)

i sprayed carb cleaner around the intake and tb and all other possible leaking spots and it did nothing to the idle, i think it was adding fuel on the trims and the code has always been there since i had all my bolt ons (and O2's) installed over a year ago, i talked with the tuner yesterday and he said most likely it was a partially plugged injector and i pulled them out lastnight and blew some carb cleaner through the injectors and it seems to be running fine, be he turned off the code so im not sure if its just hiding the problem.

Chevyscoot

iTrader: (3)

I had the same code I replaced everything also and it turned out to be the knock sensors, your tuner can change the sensitivity of them. Good luck

Tyler Z28

iTrader: (1)

but a knock would cause the elevated misfires on those 4 cylinders and then mess with the fuel trims?

Novaracer1966

I had the same problem, after knock sensor, all plug wires, all new coils, and a new ICM, I replaced the PCM and have not had any problems since.