cams and headwork question
Posted 21 November 2005 - 04:52 PM
Posted 19 July 2006 - 02:53 PM
I have a 2002 mustang gt that I put a set of comp xe270 cams in and got the stock pi heads ported. The car has been tuned at a ford dealer that does ford racing tunes on a dyno with a superchip. Ever since the heads and cams were installed the car seems to buck and jerk a little upon very light throttle. It was real bad when the car was just finished, but the ford dealer modded the computer itself a little and made it better. They said it is form the egr. Is there any way to make this problem go away completely and still pass emissions.
I don't know the specific cause, but maybe I can help you isolate it a bit. I'm assuming you hve a stick; if not I don't know if this will work. On a stock 02GT if you try what I'm going to suggest you'll get only a very mild drivetrain buck, not violent. If it's violent on your car, then I think the ECU is telling the injectors to go to a level higher than their lowest flow rate, and the superchip tune is likely the cause. If this test produces only mild drivetrain buck, then that's not the problem (tho I then don't know what is) but it's a start.
Try this: with the car thoroughly warmed up (20 miles or 20 minutes minimium), on a level road in first gear, accelerate normally to 3500-4000 rpm and hold for 20-30 seconds, then gradually remove your foot from the accelerator completely and before the tach drops below 2500 rpm. Let the compression braking take you down to idle (which I'm assuming is still about 750 rpm or so). When you reach idle the injectors should completely shut off and then iwill alomost mmediately come back on to their lowest programmed setting. When this happens, the engine will hunt from minimum to off to minimum to off, etc. which will cause a very noticeable but not severe bucking in the drivetrain as the slack is racheted back and forth. If the bucking is mild, the enjectors are properly comeing back to their lowest EC controlled setting. If severe, wither the reprograming is the problem (most likely) of some other change the dealer made is a problem. I heard of, but can't validate, that certain cat-backs can affect how the ECU interprets the O2 sensor output and can cause balky injector control, so that could be another possiblility but should also be correctable with the right reprogramming.
Good luck, and if you find what's up, let us know in a post -- I'm sure others will be interested too.
Just one other thought... those new cams I assume are not full racecams not suitable for use with ECU engines, I hope.
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