I picked up a '93 f150 with an EFI 300 about 4 months ago for $1000. It's run well, A/C works, radio works cranks right up and goes, until recently it started missing when warm. After investigation, i found a cracked and loose spark plug and replaced all 6. It seemed to solve the problem for a while, now its back. I replaced all the plug wires and it seemed better for a while, but when its warm it seems to miss bad. I also noticed that around 2 spark plugs on the head, it seems dry, no oil where there is oil all over the others, does this indicate that those 2 cylinders are running hot? and could that be the root of the warm missing? I appreciate any advice.

1993 f150 Straight 6 300 EFI
230,000 miles

 

Does it misfire more when its wet or raining out? moisture in a cracked distributor cap will cause intermittent misfires especially when its hot. The oil is probably un-related. You most likely have a leak in the valve cover gasket and its dripping oil around those other plugs, or people have been spilling oil when they change the oil over the years and it runs down some areas of the head more than others.

 

I dont believe it was raining or extra wet the times it runs bad. I will make it a point to check out the distributor cap this weekend. Thanks