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missing=bad coil?


February 1, 2005
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City, State
Detroit, MI (yeppers, redneck white boy invading D-town! :-P)
Year, Model & Trim Level
1991 XLT 4x4
91 X, been missing since the day I got it back in February. Its dropping the number 5 cylinder (middle, passenger side), and you can feel the vibration at idle and freeway speed. Overdrive frequently is unusuable due to lack of power, and it feel like the engine is going to shake itself apart. Occasionally it would kick in, and run super smooth and lots of power, but never for more than a few hours, and would randomly drop that cylinder again. I figured out it was number 5 by pulling wires off the coil until I found the one that didn't change the way the engine ran.

When I pull the boot off the plug, I can get a spark to jump to the cylinder head, but never to the plug. The plug is grounding properly to the cylinder head, and I've tried changing plugs around to eliminate the possibility of a bad plug. The coil is cracked in several places, and logic tells me that its a bad coil (even tho I'm getting a spark, I'm assuming its too weak to fire the plug off). But I don't have a lot of experience with these DIS systems, and want other opinions before I drop the $80 for a new coil.

Do you have or have access to a chiltons manual? If you can, get your hands on one they have an excellent section on troubleshooting the entire engine electrical system. Have you also considered the possibility of a bad wire ? Try swapping the wires if you can get one to reach see if it jumps with the bad wire. I had a terrible miss that turned out to be a corroded wire, just too much resistance for a solid spark.

Try replacing the wires. I had the same problem last weekend, and the plugs were fine. It ended up being a bad wire, but had no external damage.

Don't drive on a bad cylinder. the extra fuel will ruin your catalytic converters, and the unburned gas in the cylinder will washdown the oil from the wall in that cylinder, causing excessive ring wear.

Good luck.


when you are trying to find a miss. use your test light you can hook it up to ground (like normal) and then poke through the top of the wires and if it is firing the engine will bog down.(will ground out that cyl.) have you ran a compression check on that cyl.