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Super duty 5.4 misfire...

Gatorgrizz27

Well-known member
Joined
May 20, 2020
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756
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Bought a 2005 F-350 work truck with the 3v 5.4L. Guy told me it was misfiring and needed plugs and coil packs.

Replaced them all with Motorcraft plugs and aftermarket coil packs (not the super cheap ones), since it had about 5 different types of coil packs on it. Also cleaned the MAF sensor, throttle body, PCM connections, made sure the air intake and box were clear, drained the gas tank and put a new fuel filter on it since it had been sitting awhile.


It starts and runs way better than it did before, but still idles like a cold carbureted truck, and is sluggish accelerating below ~2,500 rpm. Only code is P0354, coil pack issue on #4 cylinder.

I checked all the coil pack connectors for proper 12v and ground signal from the PCM with a test light and noid light. That coil pack reads 0.8 ohms continuity, but my meter reads 0.3 ohms with the leafs shorted. From what I’ve seen 0.5 ohm is fine.

I also did a half ass vacuum leak test with carb cleaner, didn’t find anything, and found the fuel injector for the #4 cylinder isn’t getting any signal. Thought that was likely the problem, but I’ve read the PCM may shut it down due to the fault code. Cats have been removed previously also.

Next step is a compression test, but other than jumping in and troubleshooting the PCM or assuming it is fried, what else is there to check?
 
I would probably swap #4 with a different cylinder and see if the code stays on #4 or moves with the coil pack. Still could be a coil issue.

Otherwise you are on the right track I would probably compression test at least that cylinder and another for comparison. rule out any mechanical problems.
 
Move that coil to another hole, primary circuit code is most likely the coil since you say it'll flash a noid light.
 
Dad's truck (04 5.4) has been losing coils now for a year. I think by now he's pretty much replaced all of them at least twice by now. no idea.
 
Thanks, that’s my plan so far. Anyone know for sure if the PCM will shut down that injector based on that code? Weird thing is it smells like it’s running rich.
 
Depending on ECM version, yes because they don't want to burn up the cats.

That is right in the era Ford started doing that, previously running a misfire for even 20 miles was enough to plug or melt a Cat.
 
Thanks. As I said the cats have been removed, truck has 155k miles which makes me think they probably did plug up from dumping some raw fuel in there.
 
Is he putting Ford coils in it?

Knowing Dad, probably AutoZone specials. :laughing:

Probably shouldn't have said a year. More like closer to three. It sucks because the truck only has 65k on it, but the entire thing is rotted. But yea, that truck didn't hold up too well.
 
Found the issue. Apparently the brand new Motorcraft spark plug on the #4 cylinder (hardest one to get to) had the insulator and electrode come loose. Pulled it out and it was touching the strap, my first thought was “fuck, it dropped a valve and bent it.” Then I saw it sliding back and forth. Easy fix aside from wasting hours of my time. :shaking:
 
Glad you found it. Pretty frustrating when new parts are bad. Especially brand name parts. Happens too often.
 
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