Help W/ Hesitation Under Hard Acceleration

folky15

Member
May 10, 2007
10
21
13
Chicago
I'm stumped and looking to see if anyone has a possible solution to this!

2001 Bullitt with 77k miles. Car idles and runs great except when accelerating over 4000 rpm.

Right around 4000 rpm, in every gear, the car hesitates dramatically and occasionally shuts itself off. I've noticed that it also does the same hesitation when I am accelerating and hit a large bump.

I've just replaced the fuel filter and that didn't seem to have any effect on the problem. The fuel pump was replaced about 20k miles ago. Car isn't throwing any codes.

Anyone know what might be causing this?

MAF? COP? ECU? Alternator?
 
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I would check for codes anyway. Just because the service engine soon light is not on does not mean there isn't something stored. If no codes start from the basics and check fuel pressure with a mechanical Guage and verify it is within spec then go from from there.
 
Im having almost same problem except its all before 3k. once i get past 3k or WOT it runs fine. i originally had a mass air sensor code, changed that out and ran great for a week now its back to same problems but throwin O2 codes.
 
Just following up - turned out to be a COP boot that had worn out. I found this by just checking out what was loose under the hood. One of the COP's moved around more than the other ones so I replaced it ($6 part). Worked like a charm!!
I guess the engine vibration above 4k rpm and when going over bumps was enough to shake the COP and cause a misfire.
Hope this helps someone else.....