cbonjour

well i did have a stock 98 Z28. it had california emissions on it and about 130,000 miles on it. it runs smooth and is making normal oil pressure. also, it has a cold are lid, stock 2.73's. it ran a 9.15 bone stock, with the ses light on due to bad o2 sensors. i changed out the front 2 with ones that i took off of a car that didn't have problems with them, they were the stock replacements and worked. i recently had bought a mail order tune and had my egr and air deleted. it was tuned to have cats on it and stock manifolds, and i didn't request to have the back o2's deleted out, probably should have though. anyways, i took all my egr and air off and took it to the strip friday night to see what it would do. on the street it feels like it runs great, but at the strip, it ran a 9.98!!!!!!! i was pissed. i cut a 2.24 60 ft. it also threw the ses light so i had it scanned and it was the o2's. whats strange about it is that it threw 4 codes. o2 sensor circuit low voltage(bank one sensor one), o2 sensor circuit low voltage(bank 2 sensor 1), o2 sensor circuit low voltage(bank 1 sensor 1), o2 sensor circuit low voltage(bank 2 sensor one). i'm still scratching my head over why it would throw the same code twice. could something have happened and it could be reading the back one's as the front ones or could it actually be reading the front ones twice. and could this be causing my car to run way lean resulting in the bad time. please, someone give me some advise. and i don't wanna sell my car and get a different one, i can't let this beat me.

99345hp

Its not reading anything wrong, it just threw the code twice. It happens all the time. If it sees that low voltage, its going to throw the code. If the problem goes away then comes back again, it will throw the code again. Just because it says O2 sensor in the code doesn't mean its the O2 sensor. I with I had a dollar for every O2 sensor that was wrongly replaced because the code had O2 in it.

O2 sensor low voltage on both side means that the engine is running lean. You need to check for vacuum leaks, clean the maf sensor, etc. You need to find out why the car is running lean, fix that problem, clear the code, and it will run much better. The lean problem might also be in your tune.

cbonjour

thanks man. like i said, the o2's weren't new, so i am thinking about just going ahead and putting new ones on it anyways. and i did have a vaccum line, the one that goes into the top of the head on the drivers side, break and i fixed it, it was just old and broke. there is probably a good possibilty i could have another one somewhere, and suggestions on where to check? and i highly doubt i would have a speed density setup on my tune, but would that cause it to run really lean?

99345hp

any part of the tune could cause it to run lean. It wouldn't have to be speed density. You have to check everything behind the maf for leaks. Go buy 2 cans of carb cleaner and spray down all vacuum hoses and vacuum hose connections, intake manifold sealing surface to the head, throttlebody, everything that could leak intake air.

cbonjour

thanks. if i can't find the problem on my own, i know a guy that has an hp tuners and i'll have him pull my tune and see if he can find the problem.