running issues

cherrysmash · Apr 18, 2007

hi. i have a 02' GT 5-sp. with the following mods:
flowmaster A/T cat-back
bbk O/R X- Pipe
bbk MIL Eliminators
professional Products 75MM TB
Professional Products Plenum
American Thunder Plenum spacer
K&N cold air intake
C&L 85mm MAFS
March underdrive pulleys

when i'm driving on the hwy at about 50-55MPH in 5 th gear, the car bucks serverely and also if im in traffic for a long period of time on a warm day, the car loses a bunch of power. does anyone know what could be causing this? please help!!

Dragstr05 · Apr 18, 2007

If you're in 4th at 50-55, does it still buck? Trying to accelerate from 50mph in 5th puts alot of load on the engine which may just be upsetting the underlying problem.

Is the check engine light on? How many miles on the car? Were any of the mods recently done that could be contributing to the problem? On the sitting in traffic note, is the engine overheating? Any visible smoke or high fuel consumption?

Sorry for all the questions, but a yes or positive answer to any of these will help to better diagnose your problem.

cherrysmash · Apr 18, 2007

re:re: running issues

no, it doesn't do it 4th. if i put a heavy load on it in 5th it will buck real hard until about 2000-2500RPM's and then it will smooth out. it throw codes for the o2 sensors (running lean in bank 1 and 2) once in a while, especially when idling for a long period of time. it doesn't overheat or anything. just after sitting in traffic for a long time, if a was to take off hard, it feels like it lost like 100hp, but if i drive it a good period of time(maybe 5min. or so) its back to normal. i also notice that the motor rocks a little in idle, and it sounds like it has a miss to it. the plugs are new. what do u think?

the98stang · Apr 18, 2007

definetely fix the o2's if the car is throwing codes. That's at least part of the problem.

Dragstr05 · Apr 18, 2007

cherrysmash said:
no, it doesn't do it 4th. if i put a heavy load on it in 5th it will buck real hard until about 2000-2500RPM's and then it will smooth out. it throw codes for the o2 sensors (running lean in bank 1 and 2) once in a while, especially when idling for a long period of time. it doesn't overheat or anything. just after sitting in traffic for a long time, if a was to take off hard, it feels like it lost like 100hp, but if i drive it a good period of time(maybe 5min. or so) its back to normal. i also notice that the motor rocks a little in idle, and it sounds like it has a miss to it. the plugs are new. what do u think?

The codes you have, plus the rough idle and "miss" all point to a vacuum leak. Start there. If both banks are running lean, that could explain the hesitation in 5th.

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