After replacing the coil on cylinder one it started misfiring about four days later?

Tiny
SWEETIE1965
  • MEMBER
  • 2004 GMC ENVOY
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 22,500 MILES
I had this vehicle listed above for 4 years with no major problems until lately. I put a new coil on cylinder 1 because of a misfire. It ran fine for about a week then started misfiring again. So again, I changed the coil. It started misfiring about 4 days later. The coil is not in specs as far as ohms goes. It's a standard ignition coil. All others are master pro with no problem. Why is only the number 1 cylinder doing this but no there are?
Friday, January 10th, 2025 AT 2:00 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

That is a good question. Do me a favor. Switch the new one that appears to be failing with a different coil on the engine. Drive it that way and see if the misfire changes cylinders.

If you switch it with cylinder two and then you get a P0302 (cylinder 2 misfire), the coil is the problem. If the same issue happens as prior (the misfire stays at cylinder 1), we could have a faulty spark plug, a weak connection at the coil connector, low compression in that cylinder, and the list goes on.

Take a look through this link, it explains how to check the system to confirm the proper voltage reaches the coil and how to check if the coil driver is working as designed:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Let me know what you find.

Take care,

Joe
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Friday, January 10th, 2025 AT 8:16 PM
Tiny
SWEETIE1965
  • MEMBER
  • 164 POSTS
I tested the wiring with a Noid light. I also checked the spark plug to make sure the gap is correct. I checked fuel injector on cylinder 1 and it seems fine. The only things I haven't done is change coil with a different one and a compression test. I'll check the things you said then let you know what's going on with it. Thanks for the advice.
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Friday, January 10th, 2025 AT 10:04 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,264 POSTS
I would try replacing the spark plug, even though it might look okay I have seen internal defects that are unseen to the naked eye.
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Monday, January 13th, 2025 AT 12:31 PM
Tiny
SWEETIE1965
  • MEMBER
  • 164 POSTS
Okay. I will change the spark plug with an AC DELCO that's already in there now.
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Monday, January 13th, 2025 AT 2:14 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

Thanks for the update. Let us know what you find. We are interested.

Joe
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Monday, January 13th, 2025 AT 5:39 PM
Tiny
SWEETIE1965
  • MEMBER
  • 164 POSTS
I just wanted to give you an update. The coil I put on is still holding up just fine with no problem. So I guess the problem was a bad batch of coils from the manufacturer.
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Friday, January 17th, 2025 AT 1:50 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,264 POSTS
Yep, it happens, thanks for letting us know, we are here to help, please use 2CarPros anytime.
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Saturday, January 18th, 2025 AT 10:24 AM

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