1995 f150 with the 351w, its been having misfires at colder op temps, once the truck is completely warmed up the misfire goes away. I originally changed the plugs and found what looked like carbon fouling, still had the missfire. I drove about
100 miles between swapping parts, re checking timing, etc. and decided to remove the plugs and see what i could find, if anything. I found wet oil on the threads, closer to the ceramic side of the plug. The electrode is completely clean with normal heat marks, the truck is not pinging, knocking, blowing any smoke and the oil level hasnt changed at all in the last 300 miles. The truck drives amazing whenever its fully heated up. My theory is that a gasket, possibly the valve cover is swelling up with heat causing the miss to go away. Wanted to get another opinion before i start swapping them out, or if anyone has had this issue can shed me some light that would be great. Thank you!

 

miles on engine, compression check, you know you have a nice blue spark on that/those cylinders, and not a dull yellow.

 

blue marks on the spark plug? And 317k, was rebuilt 2k miles ago by a reputable rebuild shop. Im going to hook up a tester tomorrow

 

naw! (lol), blue spark(strong to burn off oil) yellow spark(weak cant burn off oil) on the plugs, did they use, new stock motorcraft copper spark plugs, could just have been rings not seated good but they are now, could replace with new and see what happens, and wow! on miles, hope mine is running at 300k,

 

heres the results to the compression test

cylinder 1 145

Cylinder 2 145

Cylinder 3 145

Cylinder4 145

Cylinder 5 145

Cylinder 6 145

Cylinder 7 148

Cylinder 8 148

the truck is bored over 030

im not seeing alot of fouling on the plugs, just wet oil closer to the top, no smoke, ticks, knocks. Just the hiccups at idle and driving…
i did a fuel test at idle and durring the hiccups the fuel pressure goes up by 1 psi, injector???

 

I can't recall which right now, off the top of my head, but try switching out for the next range "hotter" spark plug, to help burn those deposits off. (for the life of me, I can't remember if its hotter, or colder, that you need, to burn off deposits more cleanly, I end up having to re-educate myself every damn time.)

 

Thank you for the quick reply! Im kinda stumped out here. Im assuming the compression is good? would make sense to be a hotter range spark plug, i put in the copper autolites and gapped to .45 (ive read those are what the truck wants)

 

They should work. I don't use autolites.

 

what would you recommend? Ive used autolites on a few 302’s with no issues, but im open to swapping it out if it means getting this truck back up to peak perf

 

In general, if Motorcraft plugs are available, and not hideously expensive, that's what I run, if I'm working on a Ford. Otherwise, I pretty much always run NGK or AC Delco.

Lots of guys use autolites, and have no issues. It's just not been my experience, so I quit using them.

 

alright, ill probably try to swap in some hotter moto’s or NGK’s. Im pretty stumped as to whats going on with it, i hit the gas and it takes off then itll stutter as the rpms rise.

 

The Motorcraft spark plugs used to be made by the same company that makes Autolite spark plugs, as far as I know they still are. I do believe there is some difference in quality though. I personally won't use anything but those 2 brands in a Ford engine. I have had an Autolite spark plug burn out so to speak after a lot of miles. I have an old Chevy truck that uses a lot of oil and it seems to fare better with Autolite spark plugs than AC. Had to throw inn my 2 cents.