2000 Explorer Sport 4.0. I just did the heads, valves, decked, proofed. New wires, plugs. Followed the procedure to the letter. First two starts were a bit touchy, but now starts fine and purrs like a kitten at idle. The problem; under load it acts like it drops a cylinder. Any ideas? Bad plug, bad wire, fouled injector? This thing is driving me nuts. Thanks.

 

Have you checked for pending misfire diagnostic codes?

-Rod

 

Not yet. Thanks for the tip.

 

Talked to my mechanic friend today. He recommended that I scan it for coil pack break down. After fifteen years that is most likely it.

 

And a misfire diagnostic code would point that direction, but if the misfire codes only point to one cylinder, then it may not be a coil issue. Some scan tools can even access the PIDS for Cylinder Misfire Counts so you can see how many misfires are measured by an individual cylinder which can identify a cylinder that is misfiring long before it triggers a diagnostic code.

-Rod

 

Did you install Autolite 764 plugs. they are incorrectly listed for the application and will miss under load. get motorcrafts if so.

 

No autolites. I use NGK or EEE. I have better luck with both, especially the EEE

 

How much Deck height??
Too much may cause this.

 

A week valve spring can cause this also.

 

Deck height is within blueprint parameters and valve springs checked out okay.
Thanks, everybody. Its the coil pack.