Car's missing, please set me in the right direction


New Member
Jun 9, 2005
Bethel, CT
Hi, I have a 99 GT with a mongoose vortech sq kit and the mph powerpipe. Lately, the car has been missing under load. If i were to put it in say 4th gear at 2500rpm and stomp on it, there would be a constant bububububububu almost like making your lips vibrate back and forth, that's the best way i can describe it.

I have the sct xcalibrator and decided to try and datalog it. I'm not to familiar with which paramaters to test. This is what i came up with:

Red = RPM
Pink = MPH
Yellow = Short Term Fuel Trim 1
Green = Short Term Fuel Trim 2


See how it drops off real quick right before the bottom says 119? That's where it was missing like a son of a gun. What could be the problem?

I'll try different paramaters and post a graph, let me know which ones would be useful. Note, I cleaned the maf to the best of my ability already, so I'm assuming this isn't the problem.


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If possible you need to cancel cylinders tell you figure out what cylinder it is. And check that coil out. It does sound like a spark problem. Narrowing it down to one cylinder helps. Now if its a random missfire on any cylinder you have a different problem.
Well I replaced the spark plugs and everything seems okay now. They only had about 5,000 miles on them but they looked pretty blackened and one or two were even a little bent-looking. Thanks for your help guys :nice: