I have an 2007 F-150 5.4L V-8 4X4 With just over 92,000 Miles on it. So at around 90,000 miles the truck started misfiring and hesitating on acceleration and at Idle all day long no matter how long I drove it. so I assumed it was time for Plugs, and within a week I went and bought Motor-craft OEM plugs and changed all 8 of them. As soon as I finished and started driving the truck the misfiring stopped and the truck ran great.

After about 3 months or so it has now started to misfire again only this time it will misfire when I start it up in the Morning for about 15-20 minutes until I stop somewhere and shut off the engine. Then when I Restart the engine it will run completely fine the rest of the day no problems at all until the next morning and so on. So this time It actually threw a code on the OBD with a check engine light, whereas previously no check engine light ever showed up. So I had the code read and it reads Multiple Misfire cylinders 3, 5 and 7. Since I had just changed plugs I figured it couldn't be plugs again but I pulled 3, 5 and 7 anyways and checked them only to find that they were completely fine and still sparking. So next I thought maybe it's a fuel problem, (Even though I would think if it was the filter it would happen all the time or intermittently not just in the morning or when the engine cold starts) so I changed the fuel filter and checked the pressure at the rails (The filter did look like it needed changed so I changed it but pressure was normal). Start it up and still no difference, it's actually getting worse.

I'm at somewhat of a loss here I just cant seem to understand whats going on under the hood. I grew up working on cars/trucks all my life, I have a fairly good idea of what I'm doing as far as working on the truck but it almost seems as if its a ECU problem or electrical but it doesn't say anything like that in OBD just multiple misfire. What doesn't make sense to me is that I start it in the morning and drive 5 miles, stop at the gas station, when I restart it I got no problems for the day(The check engine Light usually blinks during misfire but stays on solid after it starts to run normal).

Could a MAF Sensor or an O2 Sensor be causing this until its warmed up?

If anyone could give some insight to what may be going on I would really appreciate it. I am the original owner of the truck and its never been off road 4 wheeling or anything crazy it's towed a few things but mainly highway and city use.

 

Its your coils

 

That's kinda what i was leaning towards is there a definitive way to check them with a volt/ohm meter?

Thanks for the quick reply much appreciated!

 

Hey.

No. They need to be load-tested. You are not equipped to do that. If you buy new ones, Motorcraft is highly recommended - most aftermarket units are a crapshoot - avoid Accel , no-name fleabay units, etc.

BTW - you used new boots and applied dielectric grease properly during the plug R&R, right?

Good luck
MGD

 

whens the last time you changed your oil and filter and what type of oil are your running. multiple cylinder misfire codes can be set when only one cylinder is actually dead you need to see if any one cylinder or cylinders are misfiring or if its just running poorly. these engine are built around technology so with out scan data and the like things you just have to work harder sometimes a lot harder but what do you have as far as test tools go I take it a fuel pressure gauge what about a vacuum gauge or volt meter. if your worried that spark could be jumping to ground you can take a test light or insulated wire with to open ends ground it and take the other end and trace around all the coils none should arc to your light just don't get shocked some may have issue with this but its just a suggestion.