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Old 09-02-2005, 09:56 AM   #1
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How to tell if Coils are going bad?

Hey all,

My hesitation problem remains in my '96 GT after replacing Plugs, wires, fuel filter, PCV Valve, and cleaning the Mass Airflow Sensor. So next, on to the coils. How can one tell if one is bad? Is there some way to test them?

My mechanic said that he will also test the fuel pump to see if it's functioning correctly...so as to rule that out.

Thanks for any help.

Matt
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Old 09-02-2005, 10:36 AM   #2
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Testing the coils

Matt,

you should be able to test the coil with a voltmeter if you have one. If not, just take the suspect unit to autozone . They may be able to do a resistance check on the coil pack. Good luck.
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Old 09-02-2005, 10:46 AM   #3
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Quote:
Originally Posted by 1SLOHRS
Matt,

you should be able to test the coil with a voltmeter if you have one. If not, just take the suspect unit to autozone . They may be able to do a resistance check on the coil pack. Good luck.
Thanks a lot for your help. I will do this and report with results...Thanks again. I really appreciate it.

Matt
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Old 09-05-2005, 10:27 AM   #4
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Quote:
Originally Posted by 1SLOHRS
Matt,

you should be able to test the coil with a voltmeter if you have one. If not, just take the suspect unit to autozone . They may be able to do a resistance check on the coil pack. Good luck.

Could you explain the method on how to test with a volt meter. I would like to try this on my car.
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Old 09-05-2005, 01:18 PM   #5
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JACarreira,

There is a very good write-up in the Haynes manual for checking the coil packs (pre-99 models, not the coil-on-plug coils).

Primary resistance: check the resistance between the middle (plus) and the two outside (minus) contacts inside the oval connector on the front of the pack. The resistance should be the same between all four readings, 0.3 to 1.0 ohms.

Secondary resistance is easier. Measure the resistance between each pair of terminals (7/4, 8/2, 1/6, 3/5). You have to remove the plug wires so make a sketch of the pack and wire connections and mark each wire before you take the wires off. The resistance should be the same between all four readings, 6.5 to 11.5 kohms.

Hot tips:

Be careful when removing the wires from the coil packs. The plastic clamp on each plug wire is pretty delicate so rough handling will result in breakage and you will then need a new set of wires. Squeeze, twist a little to break the 'seal' (still squeezing the clamp open), and pull straight up (still squeezing the clamp open).

Put a dab of dielectric grease on each the inside of each plug wire connector before re-installing on the coil pack.

That's the short form. Refer the the Haynes manual or similar for the full story.

HTH,

Chris
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Old 09-06-2005, 09:06 AM   #6
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NYUK, thanks for the response and the excellent info. Couldn't have said it better myself. Seriousously.
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Old 12-27-2006, 03:54 PM   #7
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Quote:
Originally Posted by nyuk98gt View Post
JACarreira,

There is a very good write-up in the Haynes manual for checking the coil packs (pre-99 models, not the coil-on-plug coils).

Primary resistance: check the resistance between the middle (plus) and the two outside (minus) contacts inside the oval connector on the front of the pack. The resistance should be the same between all four readings, 0.3 to 1.0 ohms.

Secondary resistance is easier. Measure the resistance between each pair of terminals (7/4, 8/2, 1/6, 3/5). You have to remove the plug wires so make a sketch of the pack and wire connections and mark each wire before you take the wires off. The resistance should be the same between all four readings, 6.5 to 11.5 kohms.

Hot tips:

Be careful when removing the wires from the coil packs. The plastic clamp on each plug wire is pretty delicate so rough handling will result in breakage and you will then need a new set of wires. Squeeze, twist a little to break the 'seal' (still squeezing the clamp open), and pull straight up (still squeezing the clamp open).

Put a dab of dielectric grease on each the inside of each plug wire connector before re-installing on the coil pack.

That's the short form. Refer the the Haynes manual or similar for the full story.

HTH,

Chris

Hey Chris, I just wanted to say thank you for this explanation... I've been looking for this info for a long time and all anybody ever says is to measure primary and secondary resistance... nobody ever explained where or how... Maybe i'm just a little on the slow side........ I can finally reliably test them... YAY!!!
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Last edited by dstangcruzer; 12-27-2006 at 03:59 PM.
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Old 12-28-2006, 01:37 PM   #8
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dstangcruzer:

Thanks for the kind words. I'm glad you found what you needed, too (it's kind of an old post). Actually, I just cobbled the info from the Haynes manual along with my own experience of measuring the resistances & voltages. (For less than 20 bucks, you can't beat the Haynes manual!)

Good luck,

Chris
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