JJFORD

Hello,
My F150 misfires and shakes while accelerating between 40-50 mph. Stops when i let off the gas and continues when i press again. Only in this speed range. Doesnt do it at all when i turn O/D off. Finally got a CEL flashing for a few seconds only, then shut off. Took to advance and autozone both and no code. Possibly due to the cheap scanners they use. Im thinking a bad plug or ignition coil but dont want to replace all right now. Any ideas which injector is misfiring or do i need to just replace all. Only 37000 miles on all plugs and inj. coils. thx

techrep

iTrader: (1)

What brand parts did you install 37K miles ago.. a flashing CEL is a misfire condition...with a less expensive scanner you will have to wait for a steady CEL to read which cylinder is causing the problem. I would also double check the condition of the Fuel Pump driver module (FPDM) located above your spare tire mounted to the frame..a corroded backside will cause problems also.

JJFORD

I used Motorcraft plugs and Duralast Coils. I will check the FPDM. If i hold off for a steady CEL will i run the risk of damaging the Cat converter?
thanks

Tommy J

Even though it only does it at 40 to 50 you still may be able to unplug the coils one at a time at idle and see if it affects the idle or not or have somebody gas it while you do the same. This way works some of the time but you may have to get it to throw a code

JJFORD

It finally threw me a code. Cylinder 4 misfire, next day cylinder 5 misfire. changed all spark plugs again even tho 37k miles on them. Problem is gone. all is well for now. Seems motorcraft plugs should last longer than that. Cylinder 4 a B"" to reach.

Boomshockpow

Now you say it "misfires" only between 40 and 50 and when you let off the throttle? are you sure it's not "bucking"? google a video of it if you don't know what that means. If that is your problem, try cleaning your MAF sensor and the IAC.

nevermind lol.

Tommy J

Just out of curiosity how did those plugs look with the misfire

techrep

iTrader: (1)

Yeah...post some pic's of #4 plug removed.

dsa

Wife's 2005 Lariat did the exact same thing. I had just done the plugs a year earlier so I know they weren't the issue. Bought a set of cop's from eBay for 60 bucks and have never looked back. Took about 45 minutes to replace all 8.


I didn't have time to try and diagnose which cylinder was misfiring because the issue was intermittent. So instead of scratching my head, I just replaced them all.

techrep

iTrader: (1)

yep.. if you have extra money you can just throw parts at a problem.. some people need to just replace the part thats bad..