4.2 miss need help!
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4.2 miss need help!
My 4.2 liter F150 suddenly started missing under load. A little background: It is a late 2003 and has 75k miles. It has been in my family since new, and I have had it for the last 4 years. This truck is as stock as they come, and has been well maintained.
On my way to work yesterday, it began missing. Not bad at first, but got worse. It misses while under load and under acceleration. The "check engine light" never came on. I have not put fuel in in several days, and it ran fine until now, so I doubt it is bad fuel. I started the engine after dark and looked for arcing. None visible, and I even sprayed the wires with a mist of water. I pulled the plugs and they all look normal. The gaps were all way too large, so I regapped the plugs to .054". I pulled the coil pack and it checks within range with my VOM. Can the coil pack be the problem even though it checks out on the bench? Can the large plug gaps have contributed to a coil pack failure?
I am looking for suggestions on where to start. I HATE just throwing parts at this thing, and I don't like wasting money... If I let one of the auto parts stores run a scan, will it show a code even though I have no check engine light?
I used to think of myself as a pretty good diagnostician, but then again, when I used to spend a lot of time under the hood, those cars had points, condensers and carburetors... Can anyone point me in the right direction? Thanks!!
On my way to work yesterday, it began missing. Not bad at first, but got worse. It misses while under load and under acceleration. The "check engine light" never came on. I have not put fuel in in several days, and it ran fine until now, so I doubt it is bad fuel. I started the engine after dark and looked for arcing. None visible, and I even sprayed the wires with a mist of water. I pulled the plugs and they all look normal. The gaps were all way too large, so I regapped the plugs to .054". I pulled the coil pack and it checks within range with my VOM. Can the coil pack be the problem even though it checks out on the bench? Can the large plug gaps have contributed to a coil pack failure?
I am looking for suggestions on where to start. I HATE just throwing parts at this thing, and I don't like wasting money... If I let one of the auto parts stores run a scan, will it show a code even though I have no check engine light?
I used to think of myself as a pretty good diagnostician, but then again, when I used to spend a lot of time under the hood, those cars had points, condensers and carburetors... Can anyone point me in the right direction? Thanks!!
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Thanks critter. I guess it is worth a trip to Advance Auto to borrow their scan tool. On another forum, someone suggested changing the fuel filter. Even though I don't think it is fuel related, I will go ahead and do that since its cheap... Like me! 
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Follow Up:
I bought plugs, fuel filter and a new coil pack. My suspicions have been coil pack since the problem began, so I replaced it first... Problem solved!! 
I am going to do the plugs and filter as well, but at least I can drive it now! FWIW, when I left the auto parts store, the guy behind the counter said I would be bringing the coil pack back, as they rarely go bad... Right!
I am going to do the plugs and filter as well, but at least I can drive it now! FWIW, when I left the auto parts store, the guy behind the counter said I would be bringing the coil pack back, as they rarely go bad... Right!
Logistics Pro
Joined: Jun 2010
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From: East KY
Coil pack was my problem too.
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