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if you want to see a good source of auto trouble shooting information, go on Utube and look for Southmain channel.

This guy Eric runs a small shop in NY. He spends WAYYY to much time making understandable and clear videos
on auto troubleshooting using the cars he gets into his shop. When he has issues like this, he has a PICO scope that

he checks the current pulses to the plugs or injectors to help understand where and what the problems are.
His detailed trouble shooting advice is priceless.



https://www.youtube.com/channel/UCtAGzm9e_liY7ko1PBhzTHA


Bob



Great guy. Learned a lot from him. Diagnose first before you shoot the 'parts cannon' at it.
 

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I just checked the old coil I took from my misfiring cylinder.
Primary resistance 0.6 ohm, secondary 5.5K ohm. So it's well within specs. Then I gave the coil a good look over and no sign of burning, arcing or any other problems.
Just to make sure I grabbed an old 40X magnification jewelers loupe and checked very carefully, and I found the epoxy that seals the connector socket to the top had a small crack around the outer edge where it is sealed by the epoxy. Then I found that there was also a hairline crack, difficult to see even with the loupe, going from the connector socket base to the center of the coil epoxy on the top.
So something has failed inside.
A lesson for me. Check very carefully because even if the coil tests good on the bench it can still have internal damage that will cause a misfire while running.
 

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I just checked the old coil I took from my misfiring cylinder.
Primary resistance 0.6 ohm, secondary 5.5K ohm. So it's well within specs. Then I gave the coil a good look over and no sign of burning, arcing or any other problems.
Just to make sure I grabbed an old 40X magnification jewelers loupe and checked very carefully, and I found the epoxy that seals the connector socket to the top had a small crack around the outer edge where it is sealed by the epoxy. Then I found that there was also a hairline crack, difficult to see even with the loupe, going from the connector socket base to the center of the coil epoxy on the top.
So something has failed inside.
A lesson for me. Check very carefully because even if the coil tests good on the bench it can still have internal damage that will cause a misfire while running.

Just a note on ignition trouble shooting.
If you suspect misfire, here is one quick and dirty test to possibly tell.
take the car to a very dark area at night and leave it running.
this works best when its moist outside.
open the hood and look closely at the engine.
look for electrical arcing in the coil and spark plug areas
if you see any, you have issues.


bob
 

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Testing with a meter will not show a leaking coil. A proper test is using a megger or hypot tester. It loads the coil and checks it at load. That's when they leak causing misfire
 

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Testing with a meter will not show a leaking coil. A proper test is using a megger or hypot tester. It loads the coil and checks it at load. That's when they leak causing misfire
Best coil test for electric leaks is this:
Warm idling, spritz the coil with tap water in a spray bottle. If it shows any change in the way it runs, replace the coil. If OE coil has 100K it is at risk. Been there. Pic of one of mine. Lots of others have had that crack and misfire. Oh yes, spritz this one in the pic and it went crazy. New coil, same test, no change just kept idling smooth.


-chart-
 

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If primary/secondary resistance tests show bad, coil is bad. If tests show good, coil could still misfire under load. Btdt, lol! Best to look for cracks/arcs.
 

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Best coil test for electric leaks is this:
Warm idling, spritz the coil with tap water in a spray bottle. If it shows any change in the way it runs, replace the coil. If OE coil has 100K it is at risk. Been there. Pic of one of mine. Lots of others have had that crack and misfire. Oh yes, spritz this one in the pic and it went crazy. New coil, same test, no change just kept idling smooth.


-chart-

Not so easy spraying the 3 rear coil packs for the DOHC engine :rolleyes2:
Just checked the other coils on the front bank and they have exactly the same cracking.
Makes my wonder why all the coils failed.
 

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Old spark plugs with too large a gap and / or rounded over electrodes require higher voltage to fire, putting more stress on the coils increasing the dielectric stresses and internal heating that lead to failure.
 

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Old spark plugs with too large a gap and / or rounded over electrodes require higher voltage to fire, putting more stress on the coils increasing the dielectric stresses and internal heating that lead to failure.
Agree 100%.
Might I add an internet picture? People really do this. Gross over gap over loads the coil.


-chart-
 

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