Jerking during acceleration
02-24-2011, 08:10 PM
#1
Junior Member
Thread Starter
Join Date: Mar 2010
Location: Columbia, SC
Posts: 8
Jerking during acceleration
The car is bone stock and has 57,000 miles on it. Manual.
It does not do this at full throttle. Basically when I let the car rev up at half throttle the car will jerk through the middle rpm range and then run fine above 4500-5000 rpms. I first noticed it trying to gain speed going up a hill after a redlight. It doesn't do it every time and its always a different severity. It's been happening for almost a year now.
I've taken it to the dealership twice and of course it stops doing it as soon as the tech gets in the car. I did finally get a good datalog on the car today. The only thing that I see is the short term fuel trim jumping everywhere. I know its suppose to be constantly correcting buts its all I see that's weird.
Throttle/RPM/STFT
23.52/2372.5/3.90625
34.90/2629.5/4.6875
51.37/2925.0/-3.125
56.47/3235.0/2.34375
56.47/3560.7/-0.78125
56.47/3893.7/6.25
56.07/4203.7/-0.78125
56.07/4507.0/-4.6875
56.86/4844.5/-10.9375
56.86/5164.7/0.0000
56.47/5482.0/0.0000
56.86/5795.2/0.0000
56.86/6087.5/0.0000
It seems like once the STFT goes to 0 the car runs great. The two data passes with STFT at -4.6875 and -10.9375 both have the same exact vehicle speed so the car had a pretty hard jerk right here before reving the rest of thew way without a problem. The jerks always get worse the longer you rev with the worst one being the last. The car hesitates a little, then jerks a little, then jerks pretty hard and then revs all the way to redline without jerking again.
I really need some help guys. This is driving me crazy. If you need any more information or would like to see a different log just let me know. My datalogger should pull whatever you need. Thanks in advance.
It does not do this at full throttle. Basically when I let the car rev up at half throttle the car will jerk through the middle rpm range and then run fine above 4500-5000 rpms. I first noticed it trying to gain speed going up a hill after a redlight. It doesn't do it every time and its always a different severity. It's been happening for almost a year now.
I've taken it to the dealership twice and of course it stops doing it as soon as the tech gets in the car. I did finally get a good datalog on the car today. The only thing that I see is the short term fuel trim jumping everywhere. I know its suppose to be constantly correcting buts its all I see that's weird.
Throttle/RPM/STFT
23.52/2372.5/3.90625
34.90/2629.5/4.6875
51.37/2925.0/-3.125
56.47/3235.0/2.34375
56.47/3560.7/-0.78125
56.47/3893.7/6.25
56.07/4203.7/-0.78125
56.07/4507.0/-4.6875
56.86/4844.5/-10.9375
56.86/5164.7/0.0000
56.47/5482.0/0.0000
56.86/5795.2/0.0000
56.86/6087.5/0.0000
It seems like once the STFT goes to 0 the car runs great. The two data passes with STFT at -4.6875 and -10.9375 both have the same exact vehicle speed so the car had a pretty hard jerk right here before reving the rest of thew way without a problem. The jerks always get worse the longer you rev with the worst one being the last. The car hesitates a little, then jerks a little, then jerks pretty hard and then revs all the way to redline without jerking again.
I really need some help guys. This is driving me crazy. If you need any more information or would like to see a different log just let me know. My datalogger should pull whatever you need. Thanks in advance.
02-25-2011, 12:52 AM
#3
Junior Member
Thread Starter
Join Date: Mar 2010
Location: Columbia, SC
Posts: 8
I've cleaned the MAS (with MAS specific clearner) and run injector cleaner through the car a couple of times. Maybe a bad MAS or a bad O2?
MAS readings on the pull above went from 1.99 to 15.50 smoothly. I did not log the O2 sensor but I can.
MAS readings on the pull above went from 1.99 to 15.50 smoothly. I did not log the O2 sensor but I can.
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