Since the time I got it with about 60K miles on it, my 2007 F150 with 5.4 has occasionally started missing and running very rough. This can happen on the highway or when sitting stopped at idle. It feels like it's losing more than one or two cylinders. If I turn it off and restart or put it in neutral and rev it up, the problem almost always goes away. I have changed Fuel filter and spark plugs with no improvement. What could cause this missing but not throw a check engine code?

Thanks for any ideas.

 

Just a guess here, sounds like it might be losing fuel pressure. If it starts and runs good right after shutting off, that might give it just enough build up of pressure to run decent again for a while. fuel pump?

 

Thanks for your reply. I've pretty much decided it must be a fuel delivery problem because any electrical misfire issue would throw a check engine code. I got this truck used with 44K miles on it and it stalled out soon after with a totally plugged fuel filter. It has 88K on it now, so it looks like the fuel filter needs to get swapped every 44K. Did the swap yesterday and it's OK so far.

 

Ford recommends fuel filters to be changed every 30k.

 

I have an '06 with the 5.4, about 80k. Sounds like I might be having the same problem.

Occasionally, when the engine is cold and I get on it (such as merging onto highway) I get random misfires. This has been an sporadic problem for several years, but it is particularly bad in the winter. It's also accompanied by rough idle.

I have had a few coils and plugs replaced over the years when my ECU reported specific cylinders misfiring, but it didn't make much of a difference. I also get the error "misfire on random cylinder". Air filter is clean, fuel injector cleaner every 6 months or so. Don't know where to go from here.

Any advice would be appreciated.

 

Vast majority of misfires on the 5.4 are caused by the plugs and coils. You have already replaced the plugs, so I would lean more towards the coils. An ignition misfire won't always set a code, it is just as likely to set a code as a fuel or mechanical issue. Misfire codes are set by RPM differences, which can be caused by any of the above components.
The best way to diagnose this would be with a scanner like the Ford factory tool, IDS, performing a power balance test to pinpoint what cylinder is misfiring. You can see what cylinder is causing the issue, then swap coils with another cylinder to see if the misfire follows.
Have also seen injectors, catalytic converters, mechanical components, and fuel pump driver modules commonly cause issues, but ignition components are far more common.

 

Thanks for the help forayzor. I guess I'll go ahead and replace all the coils and plugs. Not too expensive, but what a pain to get to the back ones.

 

Anytime! to get the passenger side rear two, cylinders 3 and 4, take the PCM and bracket out. Makes it much easier. Let me know if it fixes it.