2003 GMC Yukon ignition coil

KVETTY

MEMBER
2003 GMC YUKON
V8
2WD
AUTOMATIC
175,000 MILES

Have a skip in the engine. Took it to Pepboys for a check and they said #8 coil was bad. Bought a new one, same thing. Changed plug wire and plug, same thing. Swapped #7 and 8 coils same thing

What's the next step or thing to check? I don't think it is the coil at this point. Also efficiency is really bad and getting worse. Have changed both O2 sensors and fuel filter recently.

Thanks for your help.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

When you switched number 7 and 8 components, did the same cylender still miss or did it change to number 7?

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Monday, October 5th, 2009 AT 10:46 AM

KVETTY

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3 POSTS

No, problem stayed with number 8.

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Monday, October 5th, 2009 AT 5:38 PM

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

Have you checked compression in that cylender? If you remove the plug, is it wet with gas or oil? Have you checked for an injector pulse on that cylender?

I know I have a lot of questions, but I'm trying to limit things. If the coil switch didn't change things, then the coil wasn't the problem. Did you change the spark plug too? Are you getting spark to that cylender with either coil?

Let me know.

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Monday, October 5th, 2009 AT 8:25 PM

KVETTY

MEMBER
3 POSTS

How can I test the coil for spark? PLug looks good, no oil or gas build up. Did change the plug and wire anyway.

Not sure what injector pulse is, but would it cause the code for a bad coil?

Thanks.

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Wednesday, October 7th, 2009 AT 7:09 PM

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

Basically you can check a coil the same way as a spark plug. If you hold the end of the wire near the engine block or a ground, it will spark. DO NOT TOUCH THE METAL PART OF THE COIL WIRE!!! You will get one heck of a shock if you do.

Here is a how to for checking ignition spark:

https://www.2carpros.com/how_to/how_to_test_an_ignition_system.htm

As far as an injector pulse, basically you remove the electrical (one at a time) from each injector. With a noid light, you test the plug to see if it is getting power as the engine is being cranked. What happens is everytime the injector is to inject gas into the engine, you will get power to the injector. Since you have it disconnected with a light on it, the light will flash. Since the power to the injector is timed and not constant, if will flash on and off. The flash is what I refer to as the pulse.

Joe