How do you test the coils?
Thread Starter
Melting Slicks
Joined: Dec 2002
Posts: 2,480
Likes: 62
From: Middletown DE
How do you test the coils?
My buddy has the same year c5 as me and he has had 2 coils go bad and 1 may have been bad for a while...
Is there a way to test the coils to make sure they are putting out the right amount of volts?
Is there a way to test the coils to make sure they are putting out the right amount of volts?
Last edited by SmoothFRC; Nov 29, 2004 at 09:28 AM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Right here where I always am! 
Most of the auto parts stores sells a calibrated spark tester. It's a spark plug with a shield around it and a measured gap. You plug it in to the spark plug wire and attach the ground wire to the vehicle ground and turn the engine over.
I do the same thing with two phillps screw drivers. Stick one in the boot and bridge the other one from ground. I vary the gap to see how far the spark will jump and how intense the blue color is! Usually get a good 3/4 of an inch jump! Oh by the way,,,dont get zapped!
There are some resistance readings that you can take to see if the primary and secondary internal windings are good. I am at work so I can not provide them to you until later to night. Some coils also can have a bad exterior plastic coating and can arc to the valve covers or the coil electrical plug!
Before I would suspect a bad coil, I would be looking at the wires and plugs. There cheap and easy to replace. OEM wires should read 250-750 ohms end to end and have no nicks,cuts or tears in the boots or wires. Also inspect the terminals inside the boots and make sure they are not GREEN with corrosion!
Here are some pictures of problems that i found on my ZO6.
Here are a few of the things that I found after I had my headers installed. I had the poping and dead miss under load (moderate to full throttle) and loss of power.
[IMG]
[/IMG]
[IMG]
[/IMG] [IMG]
[/IMG]
The spark plug was the main issue!
[IMG]
[/IMG]
[IMG]
[/IMG]
Thats about it for secondary ignition info
Most of the auto parts stores sells a calibrated spark tester. It's a spark plug with a shield around it and a measured gap. You plug it in to the spark plug wire and attach the ground wire to the vehicle ground and turn the engine over. I do the same thing with two phillps screw drivers. Stick one in the boot and bridge the other one from ground. I vary the gap to see how far the spark will jump and how intense the blue color is! Usually get a good 3/4 of an inch jump! Oh by the way,,,dont get zapped!
There are some resistance readings that you can take to see if the primary and secondary internal windings are good. I am at work so I can not provide them to you until later to night. Some coils also can have a bad exterior plastic coating and can arc to the valve covers or the coil electrical plug!
Before I would suspect a bad coil, I would be looking at the wires and plugs. There cheap and easy to replace. OEM wires should read 250-750 ohms end to end and have no nicks,cuts or tears in the boots or wires. Also inspect the terminals inside the boots and make sure they are not GREEN with corrosion!
Here are some pictures of problems that i found on my ZO6.
Here are a few of the things that I found after I had my headers installed. I had the poping and dead miss under load (moderate to full throttle) and loss of power.
[IMG]
[/IMG] [IMG]
[/IMG] [IMG][/IMG] The spark plug was the main issue!
[IMG]
[/IMG] [IMG]
[/IMG] Thats about it for secondary ignition info
Team Owner
Joined: Mar 1999
Posts: 28,753
Likes: 9
From: San Jose/Bear Valley CA
CA Events Coordinator
I use a timing light and watch the strobe... if it is a nice steady beat... your coil is firing ok... if it skips a few beats here and there... it needs to be replaced. I had a bad coil for 3 years and 4 dealerships couldnt find the problem... the coil was it and thats how we found it.
VR
VR
