Coil on plug question... - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Engine Tunes/Mods

Engine Tunes/Mods Performance Engine Tuning/Engine Modifications

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  #1  
Old 02-18-2019, 12:50 PM
Coopspeed Coopspeed is offline
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Coil on plug question...

I just bought a 2002 Envoy with the 4.2 engine.

The previuos owner has replaced 2 of the spark plugs and coils since they were the ones causing check engine codes and rough running.

His mechanic says if you replace a spark plug you are going to cause a problem as the coils are apparently fragile when disturbed. That how it was explained to me.

The truck has 133,500 miles and 4/6 are original plugs and coils.

I’m getting the truck ready for a trip and wondering if changing the plugs would be a good idea.

Right now everything is running great. So leave it alone?

I’ve never heard of causing a problem by changing plugs before.

Does anyone know what the mechanic is referring to or have an example of causing a misfire when changing plugs?

Thanks for the advice.

Coop.
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  #2  
Old 02-18-2019, 02:26 PM
EnvoyBoy2004's Avatar
EnvoyBoy2004 EnvoyBoy2004 is online now
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At 100K miles the plug should have been changed, and AC Delco 41-103 Iridiums should be used. There just needs to be care taken when removing coils when changing plugs.
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Old 02-18-2019, 07:21 PM
princej99 princej99 is offline
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Quote:
Originally Posted by EnvoyBoy2004 View Post
At 100K miles the plug should have been changed, and AC Delco 41-103 Iridiums should be used. There just needs to be care taken when removing coils when changing plugs.
i agree 100%

having 4 of 6 plugs original is odd, doesn't make sense in the least. 4 of 6 is past its due date.



usually its change them all or none.

and as for disturbing the fragile coils, that's also bunk. just need to take basic care in removal and re installation.
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Old 02-18-2019, 09:35 PM
Coopspeed Coopspeed is offline
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Thanks. Iíll change the plugs.

Coop.
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  #5  
Old 02-19-2019, 08:28 AM
princej99 princej99 is offline
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Quote:
Originally Posted by Coopspeed View Post
Thanks. Iíll change the plugs.

Coop.
I think that's for the best.
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  #6  
Old 02-19-2019, 11:00 AM
Coopspeed Coopspeed is offline
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After watching a YouTube video on changing the plugs, I think I see the potential problem. The spring has to make good contact on both ends inside the plug boot. Plug on one end coil on other.
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  #7  
Old 02-20-2019, 07:45 PM
vansmack vansmack is offline
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I have never had a problem with coils going bad from changing plugs. I had coils go bad on their own though. I had the #1 coil replaced at Pep Boys years ago, and a month or so later it went bad again, and they had to replace it for free. I had the #3 go bad, and I replaced it. I went on a trip from Southern California to Oregon, and my alternator went out 60 miles from my sister's house in Oregon, and that killed my #4 coil, which I got replaced at the same time as the alternator. I have since replaced the #2, #5, and #6, and kept the old ones as spares. I changed my plugs at the same time I replaced those last 3 coils, and no problem with the other three coils that had already previously been replaced.
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  #8  
Old 02-20-2019, 07:57 PM
hpgrisco hpgrisco is online now
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2003 Chevy TrailBlazer LT
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FYI...at 222K miles I had my first coil failure, #2 cyl, no spark, 100% misfires, ran rough, SES light on. Replaced #2 coil. At 223K miles, transmission won't stay in overdrive. While I'm never hard on the truck and I figure with the mileage, my transmission must be wearing out the valve body. I take it to a local trans shop I used decades ago. I get a call saying the #1 cyl coil needed replacement. Trans is fine. Conclusion - a bad coil can yield different symptoms depending on if it's a misfire under load (my #1) or a complete failure (my #2). I've now ordered an AC Delco spare from Amazon. $50 for an AC Delco coil online. $360 for a shop to diagnose, replace and road test vehicle with 2 yr 24K warranty.
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  #9  
Old 02-20-2019, 08:06 PM
vansmack vansmack is offline
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hpgrisco damn $360 for diagnostics. You need to buy a good code reader to do more yourself. I bought a decent one that reads engine and ABS codes for only about $70.
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  #10  
Old 02-20-2019, 08:26 PM
hpgrisco hpgrisco is online now
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vansmack $360 was the full repair. This is the first time I ever took the vehicle for repair since I was sure it was the transmission. I felt stupid. It was a $360 lesson. I'm sharing my lesson here. I do all my other repairs/maint. Just not transmissions.
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