01 Expedition Cyl 3 Misfire When Driving Highway

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Mike Joros

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01 Expedition 5.4L 257K mikes. Had this truck since new. I drive the vehicle monthly now, only use it for medium haul drives 4 hours one way. For past 3 years. I have had issue with the truck misfire occasionally for about 10 seconds when driving after one or more hours of highway driving. Once every 6 months it will misfire enough that it throws the code that designates "misfire on cylinder #3".

Over the past I have changed out all the plugs and all the coils(with dealer coils). Since that point changed plug and coil Number 3 additional two times... I even tried switching coils around to see if it would fail on a different cylinder(it does not only fails on cylinder #3) It seems to misfire less if I change out plug and coil #3… BUT just could be my imagination cuz I still have the same problem.


The wires to the coil and leading into the harness look fine. When I start it (cold) it runs and sounds perfect, it is only when driving at 70mph for a while before it starts to act up. I ruled out sticky valve because I feel it would do this more if engine was cold not hot.


Since the engine smoothes itself out after 10 seconds and will not happen again for the next 3 hours of the trip, I just keep kicking this can down the road waiting for some sort of revelation... or a catastrophic failure…


Has anyone came across such a problem?


Any help or insight would be appreciated.


Mike
 

1955moose

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Usually an electrical item will act up the hotter it gets. The fact that the miss doesn't move, and gets better when you pop in a new coil or plug, would lead me towards the plug connection going to the #3 coil. Try a new boot on that one coil, as well as some dielectric grease. We've had members here that had a bad wiring harness leading up to the coils. If your problem was a bad injector, or wire to it, it would act up all the time, not just after a couple of hours.

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Yupster Dog

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The heater hose is famous for leaking that on that cylinder as well. When it starts to act up, stop the truck and check the T's in the heater hoses to see if they are wet.
 
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Mike Joros

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Thanks guys... looks like responses are all over the place with this one... obviously not a common problem.


I will check the heater hoses... but since I do not see any risidual antifreeze staining nor am I ever low on antifreeze so i am not hopeful.


When I changed the coils I always put new boots and grease again not hopeful that the 4th time will be a charm but will try or test anything at this point...


If the springs were soft or rockers were loose would this not make a ticking noise all the time especially when cold?


It has something to do when the engine warms up possibly "ecm" or wire harness, injector... i do not hear any clanking or ticking noises when it fails. Just seems like it is starved for gas and starts to shake.

These are the origional injectors... are they past thier lifecycle? 18 years and 257k?


I hate that I love this truck so much or I would get rid of it... I have muscle pains for a day after laying across the engine trying to get at the back cylinders.... :)
 

1955moose

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Yupster hit it. Think about it, if the hose above that cylinders just starting to spray coolant, it will get worse as it heats up. You might want to change out all the coolant hoses. At 257k your long overdue. Problems going to be finding some of the dealer only ones. You could pressure test the system, at the degauss bottle, proper way to do the hoses. But when you do that, all the weak gremlins are gonna rear their leaky little heads. Water pump, hoses, etc. Keep us posted what fixes your problem.

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Machete

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I’m thinking a faulty injector. May have a disrupted spray pattern that is intermittent.
 
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Mike Joros

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I ran some Lucas Fuel injector cleaner and premium gas last 3 tank fulls and did not re-occur YET...

As for heater core hoses above cylinder 3 leaking or spraying when hot Not sure about your 5.4 enjines but mine has a cover with a seal that nothing will get under if water or fluid got on it . As well there is no residue or evidence of any dried antifreeze anywhere on engine... so it is very unlikely it is leaking fluid on the cylinder or coil #3.

I wil posyt again if anyhting changes or I figuer it out
 

Retiredusps

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Had a coil go bad the air cond.line froze up and defrosted letting condensation drip on coil.It was under very heavy humidity condition.
 

1955moose

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Mike, we had another member that was chasing a misfire, and his turned out to be a clogged catalytic converter, go figure. I'd never heard of that causing a misfire like a coil, or faulty sparkplug. He discovered it when the muffler shop did a back pressure test. Something to look into. The test is cheap or free in some cases. The repair, not so much!

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