Misfire in 3rd @ 3300 rpm

[bill92250]

So, my 2005 4wd expy with 5.4, 120k has decided to throw a P0301 code just before the shift out from 3 to OD. Typically in a passing or acceleration situation. All plugs and coils were replaced at 108K, and #1 was re-replaced when this started. I can avoid it by easy acceleration. Any ideas?

 

[docraymund]

You could check for excessive backpressure on bank 1. Also check the cam and crank sensors.

 

[1955moose]

What type of coil/ plugs did you install? Did they come with boots. If you read other posts, the aftermarket China coils can work worse than original. Normally you change plugs and boots. The only coil that gets changed or swapped is the one that fails, you can swap a known good one to isolate problem. With only 120k I doubt you have a valve/ cylinder problem, but it wouldn't hurt to check compression on that cylinder with a compression gauge. Anyway, that's what I do. Be sure to disarm spark if you check compression.


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[1955moose]

One more thing, just realized your year has a fuel pump module mounted near your spare tire. Crawl under there and see if the connections are corroded. Real common problem with fuel delivery on these years.


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[LEOL]

I know its not an answer you want to hear, but the problem with a question like this on a forum is there are way too many variables and possible causes to even begin to make a wild guess without having more information. Misfires on an engine like the 5.4 could be anything from fuel delivery, ranging from the common module corrosion to injector problems or fuel pump... could be an intake, or even exhaust leak or plugged CATS, plug or coil problems, could even be the PCM itself.... valve problems, head leak, Timing component failure... or a combination of multiple things.... the list goes on... so there has to be some diagnosing done to even know where to start.

It really sucks to have to pay a mechanic to tell you what "could be wrong with it"... but unless you have the time and ability to diagnose it yourself, that might be your best bet.

If you can gather some diagnostic info to offer, then hopefully someone on here will analyze it and have some insight.

I am in a related scenario, and recently posted a ridiculous amount of information,... thus far it seems any actual professionals highly knowledgable in diagnosing are probably too busy fixing everyone elses problems at work to read forums and help people out for free. LoL
its a bit lengthy but You can read my post HERE if youd like an idea of various things to test for.

 

[Snag]

LEOL, you nailed it. I feel the same on many posts. And yes I have read your other post, a couple times. Without standing at the vehicle on these posts it would be very difficult to give sound direction, but these guys on this Forum really do try to give good ideas for info given. Moose is very talented and always gives good direction on his posts as well as many of the other guys..

I can't help you either on your post and maybe the others feel the same, you have had many views. Looks like you have covered a lot on your rig. Maybe like you have suggested its time for a trip to Ford and pay the diagnosis fee. I have done the same in the past, got the diagnosis and brought it home and fixed it myself.

Good luck
Gary

 

[1955moose]

One thing I've learned working on the same model of cars in the past, is that they have the same idiosyncrasies. When you have say a Ford 351 or 302 engine with a misfire at idle, you'd check to make sure the spark plug wires at #6 and 5# cylinders crossed over each other. That stopped the light misfire. All we can do on our end is throw out info that #1 either it's the most likely place to start, or #2 it worked for ourselves or other members. I've made this comment before, and let me say what I used to tell my customers. You have to fix one problem to find another. It would be great if misfires on these Suv's was fixed by just changing one spark plug, and one coil boot, but life is never that simple. And the more miles a vehicle amasses, the more things like low compression, Exaust leaks, intake leaks, and so on, makes it more difficult to get right. Hope that makes a little sense.


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