On a trip to MN I needed gas but couldn't get 93 octane so I put in 87 and some octane boost. It's pretty stock. SCT 93 tune, throttle body spacer. Just recently did plugs and coils. It had been running strong til this trip and now it misfires. Only does it when I step on it and its pulling a little and then it misfires...let up on the gas and it straightens out. Lower rpm's it has the power but above 2500-3000 it starts up again. Today I put a new crankshaft sensor and cleaned the MAS. I'm not sure where to go from here.

Thanks
Mike

 

What brand plugs and coils did you put in?

 

motorcraft

 

well after a week in the ford shop and $731 it was the spark plugs!... before I sent it to the shop I returned to stock tune...now I got the car home and installed a JLT CAI and went to tune it again and the SCT says its not married to my car and it won't let me do anything. and of course the car wouldn't run at all. where do I go from here?

 

Probably need to contact SCT.

The spark plugs causing the issue, were they Motorcraft?

 

yes they were motorcraft but he said they weren't quite the right ones

 

???? What do you mean by they weren't the right ones? Did you change the plugs before this misfire started happening?

 

Yes I did change plugs and coils about 30 days before the misfire. I can't remember the plug number but they were motorcraft with the diodes enclosed. They replace them with the standard plug design. It ran strong after I changed plugs. I also just read that the anti-sieze grease has been fouling out plugs. Some how it gets down to the tips. Anyway it's running great now.

 

Also hot my ACT straightened out and will reinstall the JLT CAN I on Tuesday