I am finally resorting to posting this....I've read every possible thread I can get my hands on regarding this issue...

So I picked up this 98 F150 with manual trans 4x4 3 door for a steal (or so I thought)...it is super clean body and interior wise.... the previous owner was the second owner and it was a local buy. He said it was throwing the misfire code on cylinder 8. I did some premeditated reading and figured I could get it to run or I'd still be money ahead if i had to rebuild it or something.

He said he had done the compression at a shop and that was good. Had the plugs, wires, and coils replaced...none of which are OEM...also did fuel filter and dropped the tank to see if it was dirty. then he decided to bail on the truck.

since buying it....I have put 3" exhaust and a series 40 flowmaster under it from the Y pipe back to see if maybe exhaust was clogged...the big cat had already been deleted. That didnt do much...

Next i decided to see how the MAF looked...cleaned it and not much changed there either...pulled the neg terminal and reset computer...then it threw codes for misfire cylinder 5, and 3.

Decided to pull the plugs and look at them....wow...they were auto lites...one had the electrode smashed and not one was gapped right...two were only finger tight...so i put in some motorcraft plugs gapped right... BOOM....purred like a brand new truck...for a tank of fuel...then it started stumbling again...threw code for misfire on 1,4 and 8. Ive ran seafoam through the tank and did the seafoam intake cleaner as well.

the coils that are on it are the MSD blaster coils and the wires are Belden edge 8mm wire. I know that OEM is the way to go on these parts but not sure they are the problem since they are new...and the truck ran so well when i changed the plugs.

not sure where to go from here....i dont think its mechanical due to it moving through nearly all the cylinders...could the ecm be a concern on this year of truck? it starts and idles fine...really stumbles under acceleration...runs better when cold...i havent moved into the injectors yet because electrical seems like it would wander before fuel would.

im sure i may have left something out and would love any assistance on this...and like i said i have done the search and read other threads...no one ever seems to solve the issue or at least confirm what it was when they do.

THANKS!

 

Sounds like a poor plugup in the harness back to the PCM.
Another possibility is the crank sensor plugup.
Go over the harness plugs for seating.
Pull them apart and re seat them.
Look at the PCM master cable plug.
You don't know what has been done before you got the truck.
Good luck.

 

any chance you can provide locations of these? or a good manual to get that shows?

thanks

 

Put your hand on the coil injector harness and follow it back.
The crank sensor is behind the A/C compressor up front at the crank pulley.
Get under and look.
Good luck.

 

looks like the crank pulley sensor plug got hot a time or two...a bit melted. still plugs and unplugs just fine though.



question regarding the injectors....should they spin pretty freely in the intake? i was checking all the plug ins and most of the injectors themselves will spin in the intake with the slightest pressure.

 

The injectors will move because they are only set in with neoprene ring seals both ends.
Good luck.