Jwill517

I have an 04 5.4 3v that I'm having an issue with a misfire and rough idle. Has thrown p0351 and p0356 codes but only after hauling a trailer for 2 hours, but only once. I have replaced the coils(2 connectors too), boots, spark plugs (motorcraft), made sure it had Motorcraft oil and filter, fuel filter, fpdcm, tested voltage to injectors and coils, checked for leaky injectors, and pulled the valve cover looking for a dropped valve. Took it to ford and they said it failed the power balance test on 5,6,7,8, 5 being the worst but only when warm. It passed the back pressure test. I ordered the adapter to do a compression test and plan on checking the oil pressure next week. No noise except from the injectors, cam phasers were supposedly replaced before I bought it. Still idles rough and misfires but goes down the road fine until a load is put on the motor. Any suggestions? I'm going crazy over this problem.

Endlessendevours

I was driving my '08 F150 a couple months ago and pulled over at a rest area to get a nap. I woke up to my truck running rough and seemed to be missing. I threw my code reader on it right quick and it gave me the same code. I reset it and haven't had a problem since.


I would like to know more about it myself.

ajack

I'm in the same exact situation. I have 05 5.4L3v with a rough idle that will jump like a misfire with no codes. It gets worse as the RPMs increase but no studdering, bucking or hard misfiring while under load. I've done nearly everything you've tested except the power balance test at ford. The only thing I've found that helps so far is to let the truck warm up real good before I take off.

A couple things that I've read that have solved issues like this that you've not mentioned.
Clean TB and MAF
Replace foam airbox seal
Pull all your cops and clean the wells and plug ends, make sure plugs are properly torqued, replace boots with proper installation of dielectric grease.
Pull your VCT solenoids and check the screens
Get your PCM flashed to latest software
Bad O2 sensors that haven't yet completely failed
Bad Cats
Bad battery
Vacuum leaks

I have hunch on mine right now. My A/C pump has a pretty loud whine right now and you can almost kind of feel it grinding when the clutch is engaged which seems to make the idle worse. Let me know if you ever figure it out. I'll let you know if I find anything too.

corey_lax

OP, clean your MAF and throttle body and get back to us. Helps a lot with idle

Jwill517

Ford said mine actually gets worse when it's warm, passes balance test when cold. I've cleaned the maf twice but not the throttle body. I've taken the plugs out and cleaned them even after changing them. All boots have dielectric grease. I've sprayed starting fluid all over with no luck on vacuum leak so far. Haven't really messed with the filter seal. I've unplugged the vct solenoids, nothing changed but I haven't taken them out yet. Cats tested good. It's only on the driver side with cyl 5 being the worst. I'm starting to lean towards fuel or oil pressure. I wish it would just die or throw a definitive code.

ajack

I know the feeling!

Definitely clean that throttle body to completely rule that out. It's cheap and fast. It probably won't fix anything but it needs done and can cause these problems.

Jwill517

Will do. It's just weird to me that one side is "bad" with one cylinder being worse but gets worse when warm. It doesn't make any noise and no codes.

papa tiger

Obviously it runs to bad to wait for it to worsen ! A vacuum test and a compression test can tell you where to start. My guess is a vacuum manifold leak is your problem. Cheapest to fix right now.

papa tiger

Try spraying it or fog it expecially around that bank.

Jwill517

I haven't been driving it, been driving the stang but snow is coming so that's not an option much longer. I did a compression test.
1-182
2-180
3-178
4-180
5-175
6-182
7-178
8-172
Cyl 5 and 6 spark plugs were really white 7 and 8 didn't look too bad.