1997 Ford F150, 4.6L engine missing

[herefish101]

I have a 97 F150 4.6L with 170,000 on it that keeps missing, I'v put in new plugs, and it worked for a day, I put in new plug wires and it worked for a day, i'm some what iffy on replacing the coil packs because of their cost and the fact that i'v tested them with an ohm meter and they ohm'd out correctly. Every once and a while I get what sounds like a backfire(pop!) and it sounds like its coming from under the hood. My guess is a backfire in the intake could only be caused by a build up of fuel in the intake, but then how does it get there in a fuel injected engine? I'm far past stumped, and I really need some fresh ideas, the truck is not worth the thousand dollars it would cost to bring it in so any ideas any of you have would be great, thanks in advance, and i'll try to keep an update going as to the diagnosis

[Scott K]

Well, to be honest, there are several more things it can be. What you have replaced so far was maintance items, so even if they havent fixed the problem, it more then likely needed to be done anyway. But with that, for $100, you could probably have had it diagnosed, and had them tell you what is wrong with it, and then you could replace the part yourself. It could be a bad injector, a shorted wire, a bad computer, sticky valve, coil pack, bad vacuum leak etc..

[herefish101]

I think thats what might have to be done. Thanks for your input, I'm just hoping that there might be a common problem that I could be overlooking.

[Jeremy airjer W]

no check engine light?

[herefish101]

Nope, no check engine light. I guess I'll drive it this week and tear the top end down next weekend, it has to either be an intake leak, or a head problem, anything else should trigger a code. But even an intake leak should trigger a lean burn code, so I guess i'm at the "thinking the worst" stage.

[Scott K]

I wouldnt be so quick to dive into it. I would splurge for the diag, then go from there. Common things on this for a missfire would be bad plug wires, you took care of that. You also replaced the spark plugs. If you have a vacuum gauge, hook that up to a vacuum source on the engine, when it is missing, watch the vacuum gauge, if it bounces more then 1 inch, you can have a bad valve. If not, I wouldnt even be thinking base engine until I ruled out everything else. Also if it misses at idle, unplug injectors one at a time, and see if there is a cylinder that doesnt effect the rpm, and how it runs when you unplug the injector. If you find that, you just narrowed it down to which cylinder it it, now you just need to figure out what that cylinder is missing, fuel, spark, compression. Being you already replaced the plugs, and wires, I would be thinking injector. Listen to that injector, to see if you can hear it clicking, just like the others are. If it isnt, ck power, and make sure the other wire is pulsing a ground at the injector, if you have power, and a pulsing ground, and the injector isnt clicking, you have a bad injector.

[herefish101]

Right on! these are some pretty easy thing to check, I'll go through your list this week while trying to decide where to take it for diagnosis, thanks for the info 4wanderingeyes.