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PostPosted: Sat Nov 29, 2014 12:50 pm 
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Year and Trim: 2005 Bonneville GXP, Cosmos Silver
I think I have a fouled spark plug. My service engine soon light flashes while driving, and stops flashing while at a stop light. It feels like a plug is fouled. I'm going to do a plug change myself, and save time and money for a $80/hr mechanic to work on it, and possibly scratch up my fenders and maybe sit his dirty ass on my suede seat inserts! My question is, how tough are the back 4 plugs to change out? The front 4 look pretty easy. But seeing how this Northstar engine is crammed into my Bonneville, it looks like not a lot of room to work with. Any advice will be appreciated.


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PostPosted: Sun Nov 30, 2014 7:59 pm 
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Never did them, but like you said, space is tight. The EGR bracket, or whatever that is, needs to come out of the way and then the coils unbolt. I know the N* coils have been known to fail also. Might be worth checking out...

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PostPosted: Sun Nov 30, 2014 9:53 pm 
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Fronts are a breeze. Rears are a light wind. As mentioned, remove the EGR (bracket and all from the exhaust header bung and you'll open up a bunch of space. You'll need to work around the main wiring harness back there too.

I find that disconnecting the main feed to the coils (one flat pack plug fed from the main harness), and unbolting the whole "cartridge" (as GM calls it), which is the aluminum bracket with all 4 coils mounted to it, and lifting it all off as the easiest method. Be sure to watch for the rubber grommet/seal that acts as a sealer between the cartridge and cam cover. Make sure that is in good shape too.

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2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

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PostPosted: Sun Dec 07, 2014 11:12 pm 
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Year and Trim: 2005 Bonneville GXP, Cosmos Silver
Thanks for the info. Any and all help is appreciated. I'm going to try this spark plug change next weekend. I've been on YouTube watching videos on how to do this. I'm most concerned about the tube that connects on the bottom. I sure don't want to drop a bolt or nut as the case may be down in there!! I was messing with it today with the engine cover off planning my attack today. By the way, are the coil bolt heads a T30 or T 40? I'd like to get the 3/8 drive socket with the Torx head already on it. I'm thinking about stuffing an old towel down between the firewall and the hot air connection just in case anything does fall down in there. Just in case. How would I know a coil is bad? I had it scanned at Auto Zone with an Actron II scanner. It said 'misfire on cylinder #5. That's it. Good being on here with such knowledgeable people to help you out.


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PostPosted: Sun Dec 07, 2014 11:49 pm 
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They're just 10mm nuts the hold the EGR flange on. it should just drop to the ground if you drop it.

Don't recall the size of the torque bit.

Easiest way to test a coil is to move it to another cylinder and if that one acts up, you know it's a bad coil.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Mon Dec 08, 2014 12:09 am 
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Year and Trim: 2005 Bonneville GXP, Cosmos Silver
Ok, thanks for the info. Hopefully it won't act up. It has 159,000 miles on it. Other than the misfire, it's been a great engine. I tell my friends it has a N* in it, and they're like 'oh no'. I guess the earlier engines got a bad rap. But it's my understanding after 2003 they pretty much fixed the previous problems. It's going to be time for 2 front struts soon and top mounts too. I'm thinking of cutting the coils 1 turn to give it a little rake. They're really good looking cars. People don't realize it's a Bonneville, which I like.


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PostPosted: Mon Dec 08, 2014 11:47 am 
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Early ones had head warping and head gasket/stud issues which is where the genesis of the "oh no" comes from. But most, after 100k, are just more "needy" in terms of maintenance than other engines.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Sun Dec 14, 2014 2:15 pm 
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Year and Trim: 2005 Bonneville GXP, Cosmos Silver
Changed all 8 spark plugs yesterday. Bought Autolite Double Platinum plugs for it. The back 4 were DEFINITELY no fun, having to deal with that hot air pump mounted on the rear. I left that stupid bracket off upon re installation. It's still pretty firmly mounted without it. The miss is still there. The #5 plug looked real bad and there was no gap on the tip and ground strap. Just a bunch of white chalkiness build up and smelling of raw gas. I'm thinking the coil isn't firing properly. Another problem, the motor sounds like it has a big time vacuum leak, originating around the back left corner of the intake (passenger side). I tried to tighten all of the intake manifold bolts I could get to. Some were amazingly loose!! I'm going to put the new coil in the #5 cylinder and take this thing to a shop to have the vacuum leak diagnosed. With all of the stuff draped all over the intake, I think I'd better leave it to a professional. If they say it's not too bad, and I could fix whatever is wrong, I'll try it.


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PostPosted: Sun Dec 14, 2014 2:17 pm 
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Year and Trim: 2005 Bonneville GXP, Cosmos Silver
By the way, the coil mounting bolt is a T30. Just thought anybody would like to know.


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PostPosted: Thu Mar 23, 2017 7:05 pm 
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Location: Indianapolis, Indiana
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I am ready to buy spark plugs for my GXP figured ac delco, anyone have the number or suggestions on which to use


Thanks


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PostPosted: Thu Mar 23, 2017 7:16 pm 
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41-987. I also think 41-950 will work too.

I am a fan of NGK also. NGK 7164 will work.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Thu Mar 23, 2017 9:38 pm 
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Thanks again! you are a wealth of knowledge, gap at .50 ?


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PostPosted: Thu Mar 23, 2017 10:28 pm 
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Yes, .050. However, all these specific iridiums and other fancy metals plugs usually come pre-gapped at spec.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Thu Mar 23, 2017 10:38 pm 
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Joined: Sat Oct 20, 2012 7:06 pm
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Location: Indianapolis, Indiana
Year and Trim: 2004 Bonneville GXP
2008 Grand Prix GXP
I needed a zero in the number, man Thanks again


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