I have a 2010 E350 super duty with a 5.4 liter engine. I bought this used and the engine had an intermittent miss on cylinders 4 and 7. We did all the replacing of plugs and coils and injectors and it still missed out on 4 and 7. So after a while cylinder 3 lost compression. So I replaced the engine with a remanufactured one. It still missed out on the same cylinders. I replaced the main engine wiring harness with an OEM part. Still no help. Replaced the computer..no help.. Bought more coils ..Still missing out on 4 and 7 . Here's the interesting part. When you're on the highway it will intermittently miss out on both of those cylinders and they drop at the exact same moment. We were observing this with a pico scope. Those 2 cylinders will miss out for 30 to 45 seconds and then quit missing out for 30 or 45 seconds. The only codes that come up are the missing out of those 2 cylinders 4 and 7. So finally I get on a toll road which has a speed limit of 75 miles per hour and found out that at about 77 miles per hour and about 3300 RPM And above those 2 cylinders never drop..So everything is new and still have the same problem {black}:crying:
So the 2 cylinders aren't exactly "dropping out" at the same moment.
The computer is shutting down their injector pulses at the same moment.
(because it's detecting misfires and that's what Ford computers do)
The thing is, I've seen the computer do this to unrelated cylinders when the issue was with another cylinder.
(It's enough to drive you crazy.)
So why is the computer doing is?
The 1st thing to do would be to try to pinpoint the offending cylinder.
I know what you're thinking. "all the stuff is new. Reman' engine.New PCM. New coils, wires, plugs."
I'm willing to assume that your remanufactured engine has good compression and that your new PCM is functioning and was programed right.
I'm not willing to make that assumption on the other parts because if all these new parts were functioning correctly you wouldn't be having misfires.
Maybe try this. Hook up your scanner. Bring up (in Mode 6), the misfire counter.
So at idle, I assume you'll see the misfire totals climbing for cylinders 4 and 7.
Turn off the truck, clear the codes.
Now, you can start wherever you want cylinder 8 or cylinder 1. Just be systematic about it.
I'll start with Cylinder 8.
Unplug the #8 cylinder coil.
Crank up the truck and look at the misfire counter.
Of course #8 will be misfiring (you just created it) but did it stop the misfires on 4 and 7?
No? Plug #8 coil back in and repeat the test on number 7, and so on.
Even when you get to #7, did unplugging its coil stop the misfire on #4?
Or when you get to #4. Did unplugging its coil stop the misfire on #7?
If unplugging a particular coil stops the misfires on the (original) misfiring cylinders, then there's the "offending" cylinder and that's where to concentrate your attention.
The Ford dealership couldn't figure it out .. 5 of the most reputable shops around town couldn't figure it out either.. One of them worked on it for 8 hours and didn't charge me because they couldn't figure it out.Every shop has started from the beginning and I have changed coils ,plugs and injectors countless times. .. All cylinders have had several different OEM parts on them..I don't even know How many new coils and injectors I have ..I kept them because they are good parts.. I'm having to drive it everyday like this and I honestly don't know when I'll have a chance to allow this vehicle to be down.. I drive it over 100 hours a week and soon will be as much as 110 hours a week..I'm looking for ideas to try when things slow down business wise..one idea I'll probably try next is I..was told that alternators sometimes create a strong backfeed that could cause a missfire..I do know if you have a small vacuum leak in the PVC tube 4 and 7 start missing but of course there is no lean codes.. The alternator will be next because I won't miss half a day doing that one.. Now that my brother is here seeing me write this is telling me he did the very thing you're suggesting..going through every cylinder unplugging each coil one at a time and so on..He's a master mechanic for thirty years.. It's a strange thing for sure.. It's also weird that it runs fine over 3300 RPMS and doesn't miss fire anymore as long as it stays above 3300 it also runs fine until about 2400 then goes into intermittent miss fires
Continuity test the wiring harness. Could be a fault on the trigger signal line for those two cylinders. Or a fried PCM.
It does the same thing with the old and new PCMS.. The old and new wiring harnesses also do the same thing.