While driving a short distance on a rural road, suddenly my truck began misfiring and the the check engine light was flashing. The auto heat was on 70 and as it was cold, the fan was on high... I slowed down and shut the Auto heat off so as to be able to listen better for the problem, when immediately upon shutting the heat off, the check engine light went off and truck ran smoothly, did not happen again with or without heat on...

Any thoughts (2004 w/5.4 liter, 50,000 miles) plugs changed last year, COPs have not been changed, fuel filter changed yearly.

Thanks in advance

 

Any codes?

 

You have a COP that is failing....I replaced mine at 76K or so due to same problem. Global Automotive has all 8 for $104 shipped. If you want motorcraft they are about $83 per COP.

 

Thanks guys... Had it checked and there were no codes, no sign of any in the history. Thinking maybe bad gas. I figure there is no need to change the COPs at this point.