Why would I have a worst skip after new parts installed ?


Asked by Oct 18, 2015 at 07:36 PM about the 2004 Ford F-150

Question type: Maintenance & Repair

Dealer said my 45 mph break down or skip was due to two faulty coils. I
replaced with motorcraft plugs, and all eight oils with  Accel coils. The engine
is a 5.4 three valve triton.
Starting it up it runs terrible worse than before replacement parts. Took it sell
apart rechecked re assemble same issue. Any guidance where I should test

9 Answers


You should have used Motorcraft coils. Accel coils sometimes don't like Fords. Also check the boots at the spark plugs.

1 of 1 people found this helpful.

Hi Bob Thanks for your info. I have no problem replacing the Accel w motorcraft. It's the only time I have ever used anything other than motorcraft. My luck. But I don't understand "check the boot" seems they fall in on their own without any room for adjustment. It's odd that it runs worse now with all 8 plugs & coils than it did before I started. I removed the plugs a second time to make sure I didn't apply to much dielectric to the plugs. I wiped them clean but it did not appear that was a problem. Reassembly proved no change a real bad misfiring shaking engine.

1 of 1 people found this helpful.

I am not guaranteeing different coils it will fix it, but the Ford 4.6 and 5.4 engines seem to have issues with aftermarket coils and sometimes they don't last long. Look for small holes burned through the side of the plug boots by the spark from the coils. If there is a small hole or carbon tracking it will cause the spark to go to ground instead of across the plug gap.

1 of 1 people found this helpful.

Do some googling and read about problems with aftermarket coils on Fords. Here is an example at the link.....http://www.f150online.com/forums/v8-engines/325901-accel- coil-packs.html

1 of 1 people found this helpful.

Bob has good info. To help narrow it down try to have the codes read to see where the misfires are

1 of 1 people found this helpful.

Thanks Andrew. I did as you suggested and i had 6 out of 8 misfire. I sent the Accel back and ordered the Motorcraft coils. I think Bobs suggestion is warranted. Plus its a finicky engine to begin with. Ill let y'all know if I'm successful or if i need to go further. Thx


Gary, keep us posted and good luck with it.


Hi Guys. Installed new Motorcraft coils still misfiring. its worse at low end but it is there at higher RPM's as well. I think i will test the injectors next. Any ideas would be welcomed.


Ok all 8 injectors give me a 12.9 Ohms reading. so they work. but that doesn't mean there clean. so if i have to remove all that wiring, hoses and fuel rail to remove them to clean them, at 140K miles am i better off replacing them? of course i still really don't know if they are even my problem. God Bless mechanics.

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