i have a 89 f250 with a 5.0L 302ci efi motor. i bought this truck about two weeks ago hadnt really been driven in the last 2years. evrything was fine with the truck for about a week and a half and then it began misfiring. it doesnt happen until 1600rpms and does alittle on idle. i have changed the cap and rotor, plug wires, checked plugs and fuel filter checked air filter looks new, ran truck off of the second gas tank stayed the same, checked egr valve and seems to be ok. nothing i have done has even slightly changed the trucks problem any advice would be greatly appreciated thanks!

 

Welcome to FTE!

Ford issued a Service Bulletin years ago for this issue:

http://www.justanswer.com/uploads/ep...ug_routing.pdf

Verify your plug wires are routed appropriately.

 

thank you for the response ill go check it out when i get to my shop in a little bit. this problem just began happening and even after i changed the wires one at a time, still the same it starts off small at the missfire gets worse the more the truck drives until it cools off again it goes back to starting point

 

I start off with the simple items, then move onto the $$bigger$$ ones.

 

I 2nd the sparkplug routing as this is my problem with my 89 F250 302/aod. The plug wire harness is missing and the wires will cross over and cause the crossfire between cylinders.

Also pull the codes from the ECU and it could tell you of any other porblems.

Bad gas also can cause a misfire, so try to get fresh gas in the engine.