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.

 

Can you scan and make sure your IAT is showing correct? and check the CTS as well, it's possible that it's leaning out causing the missfire. I would look into the COP boots, sometime they carbon track and when the engine is cold it takes more spark to light the fire, and when you tuned it last time you moved the boots and they were not losing spark, now they carbon tracked again. Boots are cheap and if there original I would replace them. Good luck

 

What do you mean by IAT and CTS(Cats?)? im not familiar with short hand online for engines ha. The COP boots are the originals so yea i can change those today and see if that helps. Thanks you for the quick response really appreciate it!!

 

The ECU sounds fine to me.

From your description it sounds very much like an issue I had with aftermarket COP's. On a cold morning star up I'd get a rough idle until reaching operating temp---shut engine off, immediately restart and the miss was gone.

This might be an issue with the boots but most likely its one or perhaps a few of the COP's failing. Re-read the DTC's for a more detailed read-out as to if or which COP consistently shows a failed circuit.

Also since you've changed plugs there's a possibility the wiring harness connectors aren't fully locked into the COP housing---that's kinda common too. A quick test is to GENTLY tug on each connector to make sure its locked on. If not those need to be changed, I use an NAPA #EC259 or similar---they'd need to replace the original factory connectors. Butt splice connectors are okay but its better to use some sort of heat shrink connector or follow Ford's advice for repairing a wire harness.

HTH

 

6 months ago, got tune up and replaced all spark plugs. About 3 months ago, the misfires and loss of power after 45mph started. Thought we had ‘coil pack’ replaced but found out it was just one coil that was replaced. I personally have no clue about working on vehicles but some times I have at least a good idea of what the problem has to do with but I’m at a loss. Both times that it was scanned no codes errored. The check engine light was on one day and never came back on. Now the fuel gauge is not working half the time. Can anybody please help me!?! From~mom that should have never moved away from my sons

 

You'll need a trusted local independent mechanic to a better more thorough inspection and diagnosis. Your symptoms could be attributed to a large number of issues, there's no way to even offer a guess with your so-far described situation.