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Old 06-05-2003, 07:53 PM
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Angry 4.6L missing once warmed up

My 1999 Ford F-150 has a miss under any type of acceleration once the truck is warmed up. Does anyone know why or how to figure this out? Could the wires need replacing, and if so, how do I figure out if they are arcing?

The other thing I read about on this site is coil replacement, what is that and where is that on the truck. What does it look like, etc. Are we talking about an iginition coil, coil resister or what?

I replaced the plugs with double platinums because the truck has 120,000 miles on it and I thought it was about time.

Please help, I need to get this done ASAP.

Thanks.
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Old 06-05-2003, 11:47 PM
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4.6L missing once warmed up

If your truck has plug wires, then disregard on the coil thing. The newer ones have a coil on each plug and have no wires. These are more prone to burn out if shorted because the only have one path to discharge. With a plug wire type ignition, the rest of the time, the coils can discharge to the remaining cylinders, taking some of the load off of it. You coils could be bad, but doubtful. Usually they will turn on the check engine light when the go bad. I am assuming that you have one or two coil packs?? The one on my Windstar went bad and quit firing #2 cyl. It missed all of the time.
To locate them, just follow your plug wires back from the plug. Should be a box with terminals for the plugwires. I am thinking on yours that there are 2 of them with 4 plug wires on each one.
I would start with a set of wires. 120,000 is a long life on todays engines. I think Ford recommends 100,000 miles. It isn't so much the lenghth of time that kills them, it is the heat and dirt.
I am assuming that it did this before you changed the plugs? Does your check engine light ever come on? Could also need new oxygen sensors if they have never been replaced.
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Old 06-06-2003, 12:31 AM
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4.6L missing once warmed up

A 99 should have COPs...coil on plugs. Each spark plug has it's own coil sitting on top of it.
To tell which one is misfiring you can have the truck scanned for codes. It might not show up any hard faults but there may be a pending code that would lead you to which cylinder is missing.
If not it will take an ignition analyzer of some sort to figure out which cylinder it is. If it was missing at an idle it would be easy to figure out which one....pull off either an injector connector or coil connector one at a time until you find one that doesnt make any difference. With a miss only when driving, a Ford dealer can hook up their WDS scan tool and watch the cylinder power balance while driving to see which one drops out. I've had to do this lots of times and it works well. It sure beats guessing
Take a look at the heater hose above #4 COP and make sure the clamp is tight and hasnt leaked any coolant onto the COP. If it has any sign of coolant on it (green stain etc) it's a fairly safe bet that it's got a problem.
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