Testing coils on a coil over plug system?

[art leong]

I need to check the coils. How should I do it?

[NewHemi]

There may be better ways.... But the best way I have found so far, is either heat/temp check on exhaust via EGT readings, or using a touchless thermometer. (bought mine at Harbor Freight for a few bucks) See if one cylinder is cooler than others.

Or if that doesnt work, then it is just brute force... replace (or if you don't have a lot of spares, rotate by putting a spare one in, and if no change, move the removed one into the next position, etc.) each one until you see a difference. No difference, no problem...

When we had problems with a coil pack, it only showed up at load, or higher rpm. At low rpm, it worked just fine.

Good luck Art!

David
The New Hemi Guy

[art leong]

I'm having trouble keeping it running when putting the car in gear. Have changed the converter (no help). Checked and recheck all wires and grounds. Changed the fuel filters (no help). Done a leakdown test (2% to 4%), looked at the top end, all cams and running gear look okay. Checked plug wires 27 to 29 ohms resistance, new plugs. Double checked timing.
When I drop it in gear it just gets crappy and stalls. I've data logged it and there is nothing showing that could cause this. What ever it is it seems to have gotten worse, before I could keep it running with the gas pedal but now it is almost impossible to keep running.
It seems to get worse as I work on it. Then get a bit better the next day.
There are no vacuum leaks, when I put my hand over the intake it reacts immediately.
I've played with the tune (richening it or leaning it) and it doesn't seem to change much and doesn't get better

[Ed Wright]

Art, good auto parts stores carry adjustable coil checkers. Very simple. If you can't find one, Snap-On used to carry them too. Their's just cost more. Set the adjustable gap to 40,000 volts. Should have a sharp blue spark. Should hear a snap each time it fires. Sounds crude maybe, but will show up a weak coil in a heart beat. Hook it to the spark plug end of the wire, you may also find a leaky plug wire.

[buzzinhalfdozen]

Art, if the engine runs when not in gear, how well does it run? does it sound normal, snappy throttle response? Though it is possible that you have an ign. problem, I'd doubt it would start at all with a bad coil, 4 cyl. engines with just 1 hole out tend to just barely run. Assuming you have headers, easiest way to check for dead hole is a spray water bottle, start engine let run a few minutes, then spray header tubes, should be instant sizzle on all. That will at least tell you if you've got a dead one without spending a dime. If you find that you do indeed have a dead cyl. as mentioned before swap coil with another cyl. if misfire follows you've got a bad coil, if not look at the control circuit for that coil. Good luck ans please let us know what you find. Joe

[Ed Wright]

A leaky wire, boot or cracked plug can show up in gear and not idling in neutral. A little de-natured alcohol or soap in the water will break the surface tension so the water will cling to the plug wire, boot & plug, instead of bead up and not cover the entire surface. That will find small leaks quicker. I prefer the alky. A jumper wire, one end grounded and the other on a thin screw driver or ice pick will help find leaks too. Run the screw driver (or ice pick) along the coil's body, plug wire, boot and plug. a good digital lab 'scope is good for checking wave forms for the control circuit. If you are used to using them you can pick out a coil with an internal problem also by using the secondary clamp. I have an old Fluke 98A that still does that kind of work really well.