How do I check ignition coils??

OK, I was driving home from school two days ago and my car started to shake really bad. I noticed something was wrong when I put the car into drive and the car started to stutter slightly. When I got up to the 45 - 55 mph range the car went into a ballistic spasm. I changed the fuel filter and no effect. I have a friend that said he had the same problem but it was caused by bad ignition coils. Does anyone know an easy way to test them(or have any other ideas on what could cause my car to do that)?

Your problem is either the coils, or the ICM (Ignition Control Module). The ICM can be removed and tested for free at Autozone or similar. The coils can be tested by:

1. Run the car in a very dark garage/street/etc
2. Use a pair of INSULATED pliars to remove the plug boots off each individual coil terminal
3. If no spark or an erratic spark, then you've found a bad coil.

Are you getting a service engine soon light (and diagnostic codes if you are)?

Also, you may wan't to mention the year in the future since lots of stuff changes from year to year ;)

Welcome to AF :D

It's a 1992. The engine says 3800. The service engine light hasn't gone off. What does the ICM look like? Is it near the ignition coils?

Ignition module is what the coils are mounted to. You can also check the resistance of the coil windings. The three secondary side readings should be very close to each other. Each of the three primary side readings should also be very close.

Ignition module is what the coils are mounted to. You can also check the resistance of the coil windings. The three secondary side readings should be very close to each other. Each of the three primary side readings should also be very close.

:1:

Removing the wires off of a coil, especially the magnavox type will kill it. As soon as the secondary resistance is gone, the coil will max it'self out trying to overcome the infinate gap. Installing a inline spark tester is a safer way to go. :2cents:

Ignition module is what the coils are mounted to. You can also check the resistance of the coil windings. The three secondary side readings should be very close to each other. Each of the three primary side readings should also be very close.

Checking the resistance of coils is not the most reliable way to confirm that an inductor is good. If you have an open winding or a catastrophic short, then you'll see it. However, if you have a shorted turn or two, an ohmeter will never pick it up. The best way I know of is to to look at the voltage or current on a scope. I prefer looking at the current waveform.

:1:

Removing the wires off of a coil, especially the magnavox type will kill it. As soon as the secondary resistance is gone, the coil will max it'self out trying to overcome the infinate gap. Installing a inline spark tester is a safer way to go. :2cents:


I said to check the resistance of the coil windings. All you do to check the secondaries is remove the 2 spark plug wires and & connect an ohm meter. The key never needs to be turned.

Checking the resistance of coils is not the most reliable way to confirm that an inductor is good. If you have an open winding or a catastrophic short, then you'll see it. However, if you have a shorted turn or two, an ohmeter will never pick it up. The best way I know of is to to look at the voltage or current on a scope. I prefer looking at the current waveform.


I agree that checking the resistance will not always find a bad coil. I'm willing to bet that it'll find the problem more times than not. Most people posting here won't have a scope.

I was in perfect agreeance with you on that. I was pointing out what Alibi said about removing the plug wires off the coil while running, sorry I hit the wrong qoute.

I usually use an old spark plug gapped to 0.200" connected to the spark plug end of the ignition wire & grounded to the engine. While cranking the engine, I observe the tester for spark. If I see a crisp blue spark, I know the coil is working properly. Now, if you only see a pale yellow spark, more than likely, you have a weak coil. I have seen quite a few coils that would pass the “resistance test”, however, not produce max voltage output.:screwy:

BTW: The specs for resistance are:
Magnavox ignition
Primary (ohms) = 0.5-0.8 (ohms).Secondary = (k-ohm) 9.0-12.0

Delco ignition
Primary (ohms) = 0.5-0.9 (ohms) Secondary = (k-ohm) 5.0-8.0

I also drive a 92 lesabre, and I had the exact same problem as you did. I parked the car in front of my friend's house, and 2 seconds later the car was having a seizure.

Drove the car down the road, struggling to hit the 50mph speed limit, all the while feelling like I was duct-taped to one of those massage chairs at the mall.

Every stop light made my car bounce like I had some really crappy hydraulics that were outta control.

Sadly, at the time I had just gotten the car (which was NOT TREATED WELL), and so I took it into goodyear (NEVER do this....when I got my brakes fixed they didn't clamp the line and fluid leaked out; GY blows), and they set me back 400 bucks for the ignition system replacement.


As much fun as playing with HV is, when you only have one car it isn't a good idea.

At the very least I can help you be sure that your problem is with the ignition coils. :2cents:

Igntion Coils, Fuel Lines, and Paint Jobs--The Silent Killer of the 1992 LeSabre.

(your paint isn't cracking/breaking, is it?)

--VrmlBasic

If you get a chance while its running smoothly..
MAYBE you can spray it with water with a spray bottle.. spraying one coil at a time.. if its cracked it may show up.. or even the wires are jumping spark spray them..

As for a bad coil you can pull the plugs associated to one of the coils an regap them to a smaller gap..Then shuffle the coils to that group.. when or if it runs better you may have the bad coil identified.. Then replace the weak coil with a good one and regap plugs to proper gap and test.

Good Luck

The ICM was bad. Got one from a 91 oldsmobile at a junk yard and runs awesome now. Thanks all!

Sweet>>>