1999 F-150 coil pack failure

I have a 1999 F-150 with a 4.6L.

I traced it down to a coil when it was missing. I had nothing going to cylinders 1 and 6. I installed a new coil pack and it ran fine for about 5 minutes and then split the bottom of the new coil pack. Now, 1 and 6 are dead again. It's the passenger side coil pack. And idea what's going on?

Are the wires known to be good? Sounds like stray HT voltage is burning the packs up.

Yes, the wires are brand new as well. Is there a resistor somewhere in the line?

No, the coils are fired directly by the EEC. You have two coil packs, one on each side, and NOT 8 individual coils correct?

Correct, one coil on each side.

That is odd.

Generally when you have back-to-back failures like this, the failed part is NOT the real problem. So I am not convinced all you need is a new coil pack. I really think, based on the failure mode, that there is something preventing the spark from reaching the cylinder(s). Either a bad wire or an open plug. I have seen LOTS of new plugs that are no good, and an occasional wire or two that will not conduct.

Unfortuneately, there is no way to check the plugs or wires without removing them. With an ohm meter, you can check the wires end to end, they should have no more than 5,000 ohms resistance (new), the plugs can be checked from the wire tip to the center electrode tip, resistances vary widly here. The big thing is that the must not be "open".

Thanks, I'll give it a test as soon as I can and let you know.

Thanks for the help.

Okay, we're still dead in the water. I checked the wires and plugs, found 2 wires with between 8,000-9,000 ohms. I took the plug wires back, got a new set of wires, new plugs and ANOTHER new coil. Hooked it all up, left the 1 and 6 wire off and started it to check for spark. I've got nothing on 1 and 6. It's dead coming out of the brand new wires, which are hooked to the brand new coil.

So, that's the 3rd set of wires, 3rd set of plugs and 3rd coil that I've put in within the last month to get this thing going.

Any idea why I can get anything out of the coil? What's upstream of that that could be bad?

There are two coils in each pack, as you have discovered, 1 & 6 are the same coil. It is *possible* that the signal (switched ground) for THAT coil pair is shorted to ground, so the current thru the coil is constant instead of switched by the EEC.

I would have to do some checking to figure out where this could happen, and exactly which wire it would be.

Any idea on where to go from here? I'm stuck.

Anyone else got any thing on this? Sorry to keep bringing it up, but everyone I have asked says "I have no idea". I'll ask one last time and then I guess I'll start selling it for parts :)

check the resistance of your coil pack where the plug wires go on from tip to tip should be 5000 ohms or more and were your plug in goes should be no more than 3 ohms. if thats ok check for power to coil packs turn the key on engine off check for power should be the same as battery voltage. make sure anytime you check for spark that the plugs are grounded. if not the secondary output will ground though the primary and short the coil and or the ecu. make sure your using motorcraft or equivalent spark plugs.