... 
There have been too many of these lately:
backfiring
Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
Likes: 0
backfiring
'02Z M6. I have just recently installed new spark plugs (ACDelco iridium) and replaced wires (MSD 8.5). The car is now backfiring only for about a block in 1st and 2nd and I cant remember if it was doing that before. Weather a factor (much colder)? Its not a daily driver, I drive it mostly on the weekends. Had the car for about a month and a half now. One thing ive tried is putting half premium and half mid-grade, that helps a little. Im going to try all mid-grade next (Chevron w/Techron). There is also water dripping from the exhaust.
The exhaust is not a constant smooth rumble on the passenger side. Driver side it is constant. The passenger side there is a "skip". No codes. Just history codes of RDCM and LDCM (thank God). How can I know for sure if there is a missfire? Check my cables with a meter is what I was thinking?
Few more misc q's:
Where are the lowering bolts on the car?
Did GM make a larger rim diam set (w/1"offset) of the magnesium stock wheels (19-20)? Does anyone else?
As far as weight, are the aftermarket larger popular wheels comparable to the magnesium wheels? TIA.. learning newb
Dave
The exhaust is not a constant smooth rumble on the passenger side. Driver side it is constant. The passenger side there is a "skip". No codes. Just history codes of RDCM and LDCM (thank God). How can I know for sure if there is a missfire? Check my cables with a meter is what I was thinking?
Few more misc q's:
Where are the lowering bolts on the car?
Did GM make a larger rim diam set (w/1"offset) of the magnesium stock wheels (19-20)? Does anyone else?
As far as weight, are the aftermarket larger popular wheels comparable to the magnesium wheels? TIA.. learning newb
Dave
Tech Contributor
Joined: Jan 2007
Posts: 19,363
Likes: 1,128
From: Dyer, IN
'02Z M6. I have just recently installed new spark plugs (ACDelco iridium) and replaced wires (MSD 8.5). The car is now backfiring only for about a block in 1st and 2nd and I cant remember if it was doing that before. Weather a factor (much colder)? Its not a daily driver, I drive it mostly on the weekends. Had the car for about a month and a half now. One thing ive tried is putting half premium and half mid-grade, that helps a little. Im going to try all mid-grade next (Chevron w/Techron). There is also water dripping from the exhaust.
The exhaust is not a constant smooth rumble on the passenger side. Driver side it is constant. The passenger side there is a "skip". No codes. Just history codes of RDCM and LDCM (thank God). How can I know for sure if there is a missfire? Check my cables with a meter is what I was thinking?
Few more misc q's:
Where are the lowering bolts on the car?
Did GM make a larger rim diam set (w/1"offset) of the magnesium stock wheels (19-20)? Does anyone else?
As far as weight, are the aftermarket larger popular wheels comparable to the magnesium wheels? TIA.. learning newb
Dave
The exhaust is not a constant smooth rumble on the passenger side. Driver side it is constant. The passenger side there is a "skip". No codes. Just history codes of RDCM and LDCM (thank God). How can I know for sure if there is a missfire? Check my cables with a meter is what I was thinking?
Few more misc q's:
Where are the lowering bolts on the car?
Did GM make a larger rim diam set (w/1"offset) of the magnesium stock wheels (19-20)? Does anyone else?
As far as weight, are the aftermarket larger popular wheels comparable to the magnesium wheels? TIA.. learning newb
Dave
check your plugs and wires. You may not have a wire on all the way or cracked a plug.
Racer
Joined: Aug 2007
Posts: 485
Likes: 0
From: Moline Illinois
Had the same problem after replacing the plugs. Turned out to be a bad plug right from the factory.
When I pulled them back out after about 60 miles one had black soot on it, replaced it with new and no problems.
On mine, it only did it when the engine was warm though, when cold it ran great. No visible damge to the plug what so ever, even put it in a pressurized test chamber at work, fired fine, only hint was the soot.
Guess what one it was-- #7.
Hope it helps.
Chris
When I pulled them back out after about 60 miles one had black soot on it, replaced it with new and no problems.
On mine, it only did it when the engine was warm though, when cold it ran great. No visible damge to the plug what so ever, even put it in a pressurized test chamber at work, fired fine, only hint was the soot.
Guess what one it was-- #7.
Hope it helps.
Chris
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Fixed TWO of these in the past 4 months for friends. They SWORE< that there was NO WAY that the plug could be cracked, damaged!
I could hear it arcing while the car was idling! I personally had a miss due to poor connection in the coil tower! 
The spark plug wire terminal pushed into the coil boot and the metal terminal was not making positive contact with the coil terminal. The result was a corroded plug wire terminal and CYL#6 miss.
Cleaned it up, repositioned the plug wire terminal correctly in the coil boot and "PROBLEM SOLVED" !!!!!!!!!!!
BC
I could hear it arcing while the car was idling!
I personally had a miss due to poor connection in the coil tower! The spark plug wire terminal pushed into the coil boot and the metal terminal was not making positive contact with the coil terminal. The result was a corroded plug wire terminal and CYL#6 miss.
Cleaned it up, repositioned the plug wire terminal correctly in the coil boot and "PROBLEM SOLVED" !!!!!!!!!!!
BC
Tech Contributor
Joined: Jan 2007
Posts: 19,363
Likes: 1,128
From: Dyer, IN
Fixed TWO of these in the past 4 months for friends. They SWORE< that there was NO WAY that the plug could be cracked, damaged!
I could hear it arcing while the car was idling! I personally had a miss due to poor connection in the coil tower!
The spark plug wire terminal pushed into the coil boot and the metal terminal was not making positive contact with the coil terminal. The result was a corroded plug wire terminal and CYL#6 miss.
Cleaned it up, repositioned the plug wire terminal correctly in the coil boot and "PROBLEM SOLVED" !!!!!!!!!!!
BC
I could hear it arcing while the car was idling!
I personally had a miss due to poor connection in the coil tower! The spark plug wire terminal pushed into the coil boot and the metal terminal was not making positive contact with the coil terminal. The result was a corroded plug wire terminal and CYL#6 miss.
Cleaned it up, repositioned the plug wire terminal correctly in the coil boot and "PROBLEM SOLVED" !!!!!!!!!!!
BC
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Thread Starter
Cruising
Joined: Nov 2007
Posts: 12
Likes: 0
Well, I pulled all the passenger side plugs out and none of them were cracked. But on one of them the tip was kind of mashed down almost touching the spark point. In other words it wasnt a .60 gap out of the box. I must have missed that when I put it in. So I replaced that one and it is no longer skipping from the exhaust. It still backfires, is this normal? Im waiting for my high flow power duct to come in to complete the Vararam setup, and then I was going to take it out for 45+ min drive above 55. I think the next step may be a tune.