Misfires, 2004 GT

Under drive pullies will sometimes cause problems with the crank shaft position sensor (esp bolt on type). Not 100% positive of the reason. However, the PCM must have an accurate CKP signal. Excessive vibration may reduce the quality of the CKP signal.

Also check the CKP sensor to be sure it is tight and correctly connected.

I seen several threads where the Steeda units are recommended for that reason.

Note, I am not an expert on under drive pullies. What is above is the limit of my knowledge. I am sure there are many more PPL out there that speak "underdrive" better than I do.

The main thing to check with a misfire indication after the installation of UDPs is the torque on the crankshaft bolt.

The timing wheel for the crank position sensor is sandwiched between the pulley hub and the timing chain sprocket. If the bolt is not torqued/tightened properly and fully, the pulley hub may not be fully seated which allows the timing wheel to "flop around" a bit. This "flopping" looks to the PCM as if there is "noise" in the crank position signal and it flags it as misfires.

Assuming you stayed OE and did not go, say, APR on the bolt, be aware that the OE bolt is TTY or "torque to yield" (i.e. single use) so get a new one. Ford's recommended installation procedure is:

- tighten bolt to 66 ft-lbs
- loosen the bolt one full turn
- tighten bolt to 37 ft-lbs
- turn the bolt an additional 90-degrees