Test coil on plug?
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Test coil on plug?
My 2001 Supercrew misses occassionally at highway speeds in overdrive under a slight load (incline).
Is there a way to test the coil on plug either on or off the engine? This would probably be too easy, but it would seem to be alot easier to solve the problem of "missing" if you could test the coils one-by-one.
Thanks
2001 Supercrew. 81,000 miles. 4.6L V-8. 4x4
Is there a way to test the coil on plug either on or off the engine? This would probably be too easy, but it would seem to be alot easier to solve the problem of "missing" if you could test the coils one-by-one.
Thanks
2001 Supercrew. 81,000 miles. 4.6L V-8. 4x4
Senior Member
Joined: Jan 2005
Posts: 130
Likes: 0
From: Dublin, OH
I don't have Ford COPs, I have a '97 with a waste spark DIS system. The high voltage or secondary side of the ignition, the coil, wires, boots, and plug, are under much higher stress under load (high throttle position) than at idle or cruising. A resistance test will NOT show coil tunneling, that is the coil passing the spark to ground within the coil under load. Don't waste your time measuring resistance, that's usually NOT the problem, it won't detect tunneling, and the following tests will detect any effects of resistance if it was the problem.
There are four ways I know of to simulate the high loads in the shop and three of them are only useful to narrow down the offending cylinder with an oscilloscope ($100's or $1000s) or firing KV meter ($100-$300).
1) Snap the throttle, high voltages for a 1/2 second or so
2) Power brake (in gear, brake, throttle), can't go full throttle, 3-5 seconds
3) Leave off for 30s to power down computer, full throttle to enter clear flood mode, hold it down, crank. This gives the max load on the secondary. (Thanks to flatrater.com, Jim Wilson for this) 5-10s
4) Use a spark tester. $5
Unless the Ford COP won't accomodate a spark tester, this is a cheap, fast, easy and foolproof way to identify all secondary problems (coil, wire, boot) except the plug itself. A GM spark tester is an ST125, I'm sure Ford and all aftermarkets are equivalent, I also have some from OTC. They look like a spark plug with a ground clip and spark from the center electrode to the side of the tester. The gap is about 3/4" which takes about the same KV to fire in the atmosphere as a .050" gap does under wide open throttle, i.e., it tests the coil, wire and boot under the same KV as when running under load.
Just take the boot off the plug, stick the tester in the boot, clip to a good ground (need a jumper wire to reach a ground for GM COPs in most cases), and start the car. You should see a consistent good hot spark. If no spark, inconsistent or noncontinuous spark, or a weak or yellow spark you have a bad coil, wire or boot on that cylinder. I expect you get all three when you buy a replacement COP. If you have a consistent hot spark, quit worrying about that coil.
Again, unless a Ford tech has a reason this won't work on Ford COPs, I'm at a complete loss as to why there is so much consternation as to whether a coil or boot is good or not. bigbronc, can you help out here?
There are four ways I know of to simulate the high loads in the shop and three of them are only useful to narrow down the offending cylinder with an oscilloscope ($100's or $1000s) or firing KV meter ($100-$300).
1) Snap the throttle, high voltages for a 1/2 second or so
2) Power brake (in gear, brake, throttle), can't go full throttle, 3-5 seconds
3) Leave off for 30s to power down computer, full throttle to enter clear flood mode, hold it down, crank. This gives the max load on the secondary. (Thanks to flatrater.com, Jim Wilson for this) 5-10s
4) Use a spark tester. $5
Unless the Ford COP won't accomodate a spark tester, this is a cheap, fast, easy and foolproof way to identify all secondary problems (coil, wire, boot) except the plug itself. A GM spark tester is an ST125, I'm sure Ford and all aftermarkets are equivalent, I also have some from OTC. They look like a spark plug with a ground clip and spark from the center electrode to the side of the tester. The gap is about 3/4" which takes about the same KV to fire in the atmosphere as a .050" gap does under wide open throttle, i.e., it tests the coil, wire and boot under the same KV as when running under load.
Just take the boot off the plug, stick the tester in the boot, clip to a good ground (need a jumper wire to reach a ground for GM COPs in most cases), and start the car. You should see a consistent good hot spark. If no spark, inconsistent or noncontinuous spark, or a weak or yellow spark you have a bad coil, wire or boot on that cylinder. I expect you get all three when you buy a replacement COP. If you have a consistent hot spark, quit worrying about that coil.
Again, unless a Ford tech has a reason this won't work on Ford COPs, I'm at a complete loss as to why there is so much consternation as to whether a coil or boot is good or not. bigbronc, can you help out here?