Spark Plug Coils
Hotshot
Joined: Jul 2005
Posts: 11,931
Likes: 180
Normally if you get a miss fire code on a specific cylinder, the coil is the problem 90% of the time. I just keep a spare set and change out one everytime i get a code. Never been anything else yet, but coil failure.
Senior User
Joined: Sep 2003
Posts: 268
Likes: 3
From: Florida
I recently replaced my plugs. I checked the resistance on every coil with an ohm meter. Mine were all between .6 and 1.1 Ohms. They all work fine. Ohm them out, if they are short, or open, replace them. I'm sure someone has a better suggestion...just my 2 cents.
Elder User
Joined: Mar 2005
Posts: 521
Likes: 1
From: Southern New England
He who does not utilize a meter is doomed to failure in my opinion. It is an extremely useful tool.
How to test a coil on plug type coil
Each coil is held in place by a single bolt; take out that little bolt. Disconnect the electrical connector to the coil, and then the coil and wire. You can test the coil with a digital ohmmeter.
There are two wires inside the connector and then a larger one that goes to the plug.
test across the two small connectors for the primary windings, and then from the little one that is marked bat or B+ to the large wire that goes to the plug for the secondary windings.
Using a digital voltmeter.
The primary circuit from B+ to tach should be 0.3 - 1.0 ohms
The secondary windings (B+ to plug wire) should measure about 5.9K ohms.
If you have zero resistance the coil has an open winding and is NG.
How to test a coil on plug type coil
Each coil is held in place by a single bolt; take out that little bolt. Disconnect the electrical connector to the coil, and then the coil and wire. You can test the coil with a digital ohmmeter.
There are two wires inside the connector and then a larger one that goes to the plug.
test across the two small connectors for the primary windings, and then from the little one that is marked bat or B+ to the large wire that goes to the plug for the secondary windings.
Using a digital voltmeter.
The primary circuit from B+ to tach should be 0.3 - 1.0 ohms
The secondary windings (B+ to plug wire) should measure about 5.9K ohms.
If you have zero resistance the coil has an open winding and is NG.
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
There is a time and a place to use any specific tool. Attempting to diagnose a faulty coil, other than one with a gross failure, with an ohmmeter will do little except waste time.
Out of all of the bad coils I've replaced over the years, not a single one of them would have been diagnosed with a multimeter (which I'm an expert at using, BTW, having used one for almost 40 years in my daily work).
No. If you have a "zero resistance" where you should have some resistance, you have a short. If you have infinite resistance, you have an open circuit.
Coils usually fail due to breakdown of the internal insulation that allows high voltage to leak from one winding to another adjacent winding. This results in a reduced spark voltage and the subsequent misfire in the affected cylinder(s).
Out of all of the bad coils I've replaced over the years, not a single one of them would have been diagnosed with a multimeter (which I'm an expert at using, BTW, having used one for almost 40 years in my daily work).
If you have zero resistance the coil has an open winding
Coils usually fail due to breakdown of the internal insulation that allows high voltage to leak from one winding to another adjacent winding. This results in a reduced spark voltage and the subsequent misfire in the affected cylinder(s).
Go Bills !
Joined: Jan 2008
Posts: 2,778
Likes: 65
From: Buffalo, NY
Agreed. They work or they don't (misfire). Had a friend that didn't want to spend the money on a new coil and was using his meter stating there was nothing wrong with it.. I grabed a spair coil, drove over there, Dunked in a new coil, Grabbed a beer out of his fridge and said "your welcome". Leave the meter in the drawer when it comes to cop's. I get cheap coils off of ebay. They are cheap enough i have a bunch laying around.
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