robs85ss

Hello everyone, I picked up a nice 98 trans am over the summer. It has 141,XXX on it and is stock except for an SLP LM1 cat-back and K&N air filter (Stock airbox). I took it down to the Wildwood NJ car show this past weekend. It is about a 100 Mile trip one way for me. It ran great until about mile 70 on the way down, it just had a only slightly noticeable misfire. I thought it was my imagination. I stopped at mile 95 at a Wawa, restarted and went looking for a parking spot. after sitting in traffic for a while It set the SES light and would not rev over 2k rpms. It would start breaking up badly. It sounded like a 2 step rev limiter. I Shut it down and let it sit for a few minutes and it fired up and ran fine. Driving it home, the SES light was on until I stopped for gas. when I restarted it went off. It ran fine until about 60 miles. It started the same thing again. When I restarted after a few minutes it would rev ok ,but break up at 4k rpms then as it sat idling the point at which it would break up and not rev got lower and lower until it was not driveable. I have read through many threads, but I have not found anything matching my symptoms completely. I am planning on replacing the crank position sensor, but I just wanted to know if anybody has had this problem before and is there more to it. I am not very familiar with LSX engines. It just seems like a heat related and definitely driving time related problem.

Thanks for any advice.

Rob

thunderstruck507

iTrader: (18)

Sounds like a fuel issue to me. Either clogged filter, water in the gas, or maybe cavitation from heat in the pump?

robs85ss

Thanks for the reply, I had a chance to hook up a fuel pressure gauge this past wekend. While I couldn't replicate the misfire, I did come up with 58 psi steady at idle and cruise and 50psi at full throttle. It never dipped below 50. I drove the car for an hour and a half. I plan on taking it for a long highway drive to see if I can get it to happen again. The car feels down on power right now. It runs smooth, but it just feels flat. The transmission seems to not be shifting as crisp either. Other than a transmission (auto) is there anything else that wouldn't set an SES light that would cause the lackluster performance and mushy transmission? I would like to get the car in good running order before the Ocean City MD fall cruise next week.

Thanks for any insight.

Rob

robs85ss

Hello all, I was able to grab a short video of the fuel pressure gauge while the missfiring was happening. at idle, it has a steady 58 psi fuel pressure, but as you rev and the missing gets worse the fuel pressure spikes quickly. Is this because of the misfiring or something else? It really never drops below 56 psi unless I am at WOT then it drops to the low 50s. From what I have seen it never has dropped below 52. Of course I can't do much more than 1/4 throttle when the problem shows up. After this run, I shut the car down and fired it up five minutes later, it ran fine, but withing a few minutes started acting up again. Right when the problem began, it set the P0336 code again.

Sorry for the lack of volume, it was useless and annoying camera on dash squeaking, so I muted it.

Thanks for any ideas/ help

http://s127.photobucket.com/user/85m...3bd4b.mp4.html

Rob

robs85ss

Is it possible the car is going into limp home mode?

redbird555

iTrader: (14)

sounds like you might have abad crank position sensor. i had a similar issue where mine would break up around 5k and sounded like it had a 2 step. never threw any codes so it took a while to track down

robs85ss

Your were right redbird, it was the crank position sensor. I put about 200 miles on since Friday and so far so good.

Thanks,

Rob

BRUTL

iTrader: (27)

if you were popping a P0336, that shoulda pointed you directly to the CKP