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03 Gt 5-Speed bucking or hesitating to accelerate in lower gears

New User
Posts: 1
Joined: 12/10
Posted: 12/30/10 03:33 PM

I have a 2003 Mustang GT 5-Speed. I purchased it when it was completely stock except some cat back exhaust work. Since then I have added a cold air intake kit, 70mm throttle body + plenum, SCT tune, short tube headers, off road X pipe, 3.73 rear gear, and a short throw shifter. The car currently has about 26,00 miles on it. My problem is the car bucks in gears 1-3 at low revs, however this doesnt happen all of the time. It tends to happen a lot driving thought our alley in first gear. The only way to stop the vehicle from carrying on is to shift into a higher gear. This also happens between second to third gear if I accelerate fairly hard and get off the gas. When the I continue to accelerate it will then start bucking sometimes until I shift into third. In all situations the car will continue to buck like this through the rpm's however the car will accelerate like this but much slower until shifted. I just want to make sure I mention that the car did this when I first bought it.

  I would appreciate any help with trying to solve this problem.
Thank you  

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Posts: 194
Joined: 02/10
Posted: 12/31/10 05:00 AM

until somebody else comes up with a perfect answer...

i was wondering if you have a scan tool to monitor the air flow through the maf sensor...  some scan tools can graph the data...

what might be happening is the original ford throttle body being slightly smaller and the inlet duct more restrictive... you might be setting up a resonance pulse in the air inlet duct that will cause the air flow to surge through and then slow down surge through and slow down...

since the fuel flow is controlled by the maf sensor.. the surge calls for more fuel... the slow down calls for less...  with the increased volume... you are stuck in this weird waves bouncing back and forth messing with the air fuel ratio...

most better OBD2 scan tools have the ability to display graphed data streams of some of the sensors..  

i just worry that this pulse reversion in the inlet duct might be happening to fast for the ECM to monitor and to send the rapid changes to the scan tool..... the internal operations of the ECM are probably much faster than the data rate to the OBD2 plug..

one last thing from this late night session.. i am taking that this is an engine surge... NOT the clutch damping springs bouncing the car back and forth at the slack in the drive train is wound up ...  

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