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Old 12-21-2010, 11:08 AM   #1
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Default 5.4 engine miss under acceleration

I'm dealing with an intermittent engine miss when under acceleration. I swapped out a blown 5.4 engine (145k) in my 2001 expedition. I swapped in a 85k mile 5.4 from a running 2001 Expedition. I was able to drive the donor vehicle prior to pulling the engine and it ran just great. Thanks to the help of this forum, I did the engine swap by myself in our driveway (a Bear).

Since the swap ( a year ago), I have an occasional miss in the engine. It flares up when I let off the gas (for example coasting down a hill) then get back on the gas. It will also happen if I stab the gas pedal or attempt to accelerate heavy as when merging onto the freeway; It runs good for a couple of seconds, then starts falling on its face.
If I feather the heck out of it, and drive like a Granny, it will never miss a beat. It pulls our 4500 lb. travel trailer no problem-as long as you feather the gas.
I just had the vehicle smogged (CA.) and it passed all tests with flying colors. No "check engine" light has ever come on. It's a 2nd family vehicle that gets driven only about once a week, but I'd like to get it resolved. I'd really appreciate any input you folks may have. Thanks.
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Old 12-21-2010, 11:42 AM   #2
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When was the last time the plugs were changed? Fuel filter? Air filter? Have you tried cleaning the MAF sensor? It sounds like you have an ignition coil going out.
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Old 12-21-2010, 02:15 PM   #3
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Had the Same problem with my 2007 F 150 with the 5.4L in it after changing every filter plug and having all coil packs and ignition module checked at 85,000K I ended up taking it to Ford and they had to replace my throttle body and exhaust gaskets. After all that have not had a problem since then. I don't know that this is the case for you, but I would have never thought that was the culprit on mine. It has ran perfectly since then and just turned over 103,000K
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Old 12-21-2010, 02:25 PM   #4
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yeah sounds like a vacuum leak. or a coil pack. if any of the intake type gaskets start failling at hight vacuum surges the engine will be more prone to stumble. you can do a vac pressure test.... buy a new coil keep the old one... after replacing the new coil if its still ****ty then put your old coil back on and return that **** cus it aint it. visually look at all pressure sealed surfaces you may see the problem?
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Old 12-21-2010, 03:59 PM   #5
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New plugs at 65k. Air filter is new. Fuel filter hasn't been replaced and should be, so I'll start there. It's a cheap stab. Good advice on cleaning the MAF sensor-I'll knock that out too.

I proactively replaced all the vacuum lines when I swapped the engine. Possibly I have a cracked vacuum T as I didn't change them?
I got under the hood and man handles all the electrical harness plugs, etc. under the hood.

Coil sure sounds like a possibility.
I'm hoping to solve myself if I can w/o throwing spendy parts at it. before taking it to my mechanic to have it diagnosed on the scope. Any other minor stuff I might check?
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Old 12-21-2010, 05:54 PM   #6
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I would like to commend you on your engine swap. I am still looking forward to my first 5.4L swap to really appreciate your undertaking. According to other members, these engines take their sweet time for the engine miss fire to be pin pointed down to cylinder location. Keep having the codes read and hopefully it will talk to you shortly. Good luck and nice job.
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Old 02-03-2011, 12:44 PM   #7
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sounds like you have a knock sensor gone located in the top of the block under the dome ,bit of an hassel to replace but will cause the truck to die right down when you want lots of power,but like you said feather it and works just fine,had to replace mine costed 45$ and about 3 hours work,well worth it..good luck
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Old 02-03-2011, 12:44 PM
 
 
 
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