: How to check for bad ignition coil?

Infamous Lac
04-26-06, 01:50 PM
I have a multimeter where do I check the resistance at? I have recently been experiencing misfires at low and high rph but not in the mid range. I have changed plugs and wires, but it didn't work. I have 104,000 miles on mine. And the problem started about a week ago after a trip to the gas station. Also one day I was running the AC at a stop light and the MPH read 20 mph I turn it off then it went away weird.

Infamous Lac
04-26-06, 08:27 PM
I know someone can explain this! Should be pretty simple.

04-27-06, 09:24 AM
You could always buy a good coil and switch it out one at a time. :D
I'll check my FSM when I get home to see if it has anything about coil voltage for ya.

Infamous Lac
04-27-06, 10:11 AM

04-27-06, 06:04 PM
To check if you have a bad coil remove all the plug wires and have someone crank the car while you stand back and watch the coils. If they are good the will arc between the two posts. If one does not arc it is bad or weak and needs to be replaced. What I did was swap a good one with a bad one to make sure it was the coil and not the ignition control module. One warning, BE CAREFUL, these coils can put you in the hospital if they arc and hit you. they should only arc between themselves and if they don't you have much bigger problems on your hands.

04-28-06, 02:43 AM
Are the N*s coils that powerful? I've been hit with 45kV from the coil in my 75, and the DIS on my parents SHO, neither of them have been that bad. In fact no worse than 220VAC you might find in a home (yes I'm shock prone.)

04-28-06, 10:14 AM
The coil in your 75 goes to a distributor that fire all the cylinders, these coils are used for only 2 cylinders so they might be more powerful, i don't know. All I know is that I was warned be several mechanics that if you get hit these coils will hurt you. I just figure its better safe than sorry. I don't want someone coming back here and saying that they did what i told them and they got hurt, thats all.

Infamous Lac
04-28-06, 10:40 AM
Hey this sound dangerous! Anyone know how to check them with a multimeter, im really not trying to feel like the Doc on Back to the future part I.

04-28-06, 12:26 PM
It isn't dangerous as long as you stand back while you have someone crank the engine, you only need to crank for about 5 seconds. It is the quickest and easiest way to check the coils. Otherwise just buy a new one and keep changing them out until the miss is gone. the coils are only about 40-50 dollars each. I know when mine were bad they didn't miss untill the engine was hot, when it was cold they worked enough to not be noticable. i don't know how to check them with a multimeter, does anyone else here, have you tried searching on the forum? If you have a car with the same type of coild you could take one off of them.

04-28-06, 01:07 PM
I got this from my AllData account. I have a 96 Eldorado. If you remove the plug wires resistance should be 5k-8k ohms between the coil towers.


Primary Resistance Not Specified

Secondary Resistance 5,000 - 8,000 ohms NOTE: Secondary resistance measured across each coil's two towers with spark plug wires removed.

NOTE: Winding resistance (ohms at 80°F or 27°C)

04-28-06, 09:06 PM
I just pull the spark plug wire and check for spark

Infamous Lac
04-28-06, 11:20 PM
Well I did like 93green said, only I did it one coil at a time and found out coil that sparks 5 and 2 wasn't sparking. Picked up a new one form Autozone for $30 and now its PERFECT. Thanks to all who helped.

04-29-06, 08:12 AM
I actually never thought of doing them one at a time, probably is safer. I just told everyone what my mechanic told me, glad it works and the car is running fine.