P0304 - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 19 (permalink) Old 06-30-2019, 09:44 AM Thread Starter
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P0304

Soooo, I was out playing around in GXP 715 and when I hit 5k rpm she started running rough and up popped the check engine light. Quick check showed P0304. Car idles fine but gets rough when trying to accelerate. My plan is to replace plugs and wires (the original ones are still in) and see if that fixes it. Any suggestions are welcome!

2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #2 of 19 (permalink) Old 06-30-2019, 11:25 AM
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When you pull the plug wires, see if any were loose or look damaged or worn. Fresh plugs and wires is where I would start also.
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post #3 of 19 (permalink) Old 06-30-2019, 08:43 PM Thread Starter
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And what plugs are you folks running? Iím planning on NGK TR5 and ACDelco wires.

2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #4 of 19 (permalink) Old 07-02-2019, 06:16 AM
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Don't you just love that back one on the passenger side? Better than a Denise Austin workout, or yoga with goats. Now that I think about it, may want to do both before changing that one.

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post #5 of 19 (permalink) Old 07-02-2019, 08:42 AM Thread Starter
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Originally Posted by TonyKarter View Post
Don't you just love that back one on the passenger side? Better than a Denise Austin workout, or yoga with goats. Now that I think about it, may want to do both before changing that one.
I learned to do that one first, makes the rest look easy
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2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #6 of 19 (permalink) Old 07-02-2019, 09:33 AM
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DOD lifter?
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post #7 of 19 (permalink) Old 07-02-2019, 09:34 AM
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PBM G8 GXP M6-Self flex fuel tune,OBX LTs, Kooks A/B, Monster clutch, 3.45 gear,LSA S/C, cam, fuel system, stock block and stock heads, 12 PSI.
Best e.t 10.41/ best mph 138.7 Half Mile: 168.3 mph
2007 TBSS-Self tune, bolt ons [email protected], 1,560 D.A
1991 GMC Syclone- Self tune/catback [email protected], 4,200ft D.A
https://www.youtube.com/channel/UC0o...xsBDzFImcyBfeA
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post #8 of 19 (permalink) Old 07-02-2019, 11:23 AM Thread Starter
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Quote:
Originally Posted by STAGEUP View Post
DOD lifter?
Come to think of it, the AFM/DOD hasnít worked right on this car since 2009
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2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #9 of 19 (permalink) Old 07-02-2019, 02:35 PM
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Why would a GXP have DOD? Not in an LS3. Why would you think about running cheap standard plugs?
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post #10 of 19 (permalink) Old 07-02-2019, 03:07 PM
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Why would a GXP have DOD? Not in an LS3. Why would you think about running cheap standard plugs?
The joke went right over your head. LOL!!!!!!!!!!!!!!
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PBM G8 GXP M6-Self flex fuel tune,OBX LTs, Kooks A/B, Monster clutch, 3.45 gear,LSA S/C, cam, fuel system, stock block and stock heads, 12 PSI.
Best e.t 10.41/ best mph 138.7 Half Mile: 168.3 mph
2007 TBSS-Self tune, bolt ons [email protected], 1,560 D.A
1991 GMC Syclone- Self tune/catback [email protected], 4,200ft D.A
https://www.youtube.com/channel/UC0o...xsBDzFImcyBfeA
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post #11 of 19 (permalink) Old 07-09-2019, 10:11 AM
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I've just used the AC Delco plugs and wires. The original wires look a little nicer than the Delco spare wires but aren't really better: when removing them, I've managed to tear half of them apart: the clamp that holds onto the spark plug does that stronger than holding onto the wire itself. And no, you can't grab the end of the wire with a tool, that part is covered by the steel heatshield. The plug sockets on the wires have been coated inside with some kind of lubricant from the factory but after 10 years that lubricant seems to work more like a glue. So every time you decide to pull off a wire, make sure to have a spare to replace it.

But unless you pulled on the wires, they don't seem likely to fall apart on their own. So perhaps check the coils? (Or change the plugs and wires, and if that didn't help, check the coils). If I remember right, you can detect if a spark plug doesn't work by driving a timing light from its wire.

The right rear plug was a bit annoying but not THAT bad, nothing like the plugs on 4th-gen Camaro. It could definitely use a bit more room behind it but I can't remember anything specific, did I use a U-jointed wrench extension or just managed to insert a thin wrench head?

Here is an interesting thing: I've measured the gap on the plugs I took off, and it matches the gap on the new plugs as they come from the factory, about half the gap recommended by the manual. So why do they bother to specify the gap if they don't follow it form the factory?
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post #12 of 19 (permalink) Old 07-11-2019, 07:55 PM Thread Starter
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Plug gap. Service manual says .060 but I keep reading about folks using .040. What are you guys using?

2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #13 of 19 (permalink) Old 07-11-2019, 08:04 PM
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Originally Posted by GXPaycheck View Post
Plug gap. Service manual says .060 but I keep reading about folks using .040. What are you guys using?

The factory plugs were more like 0.035. I've set the new ones to 0.060, and it seems to have made no difference whatsoever. So I guess it just doesn't matter much.
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post #14 of 19 (permalink) Old 07-12-2019, 09:38 PM Thread Starter
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I think I found the problem
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2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #15 of 19 (permalink) Old 07-13-2019, 06:35 AM
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Indeed the spark plugs look worn and might very well remedy the problem. By the which spark plugs and wires did you decide to purchase?

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post #16 of 19 (permalink) Old 07-13-2019, 10:34 AM Thread Starter
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AC Delco 41-162 plugs, and 748RR wires. Stock stuff. Runs mo betta now
I'm surprised it ran at all with those plugs.
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2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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post #17 of 19 (permalink) Old 07-13-2019, 12:03 PM
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Man, you got your moneys worth outta those plugs.
Not a good one in the lot now.
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post #18 of 19 (permalink) Old Yesterday, 04:45 AM
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How many miles on those plugs? (Posted Same question on the other forum)
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post #19 of 19 (permalink) Old Yesterday, 05:27 PM Thread Starter
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How many miles on those plugs? (Posted Same question on the other forum)
70k.

2009 G8 GXP, #715 0f 1829 (#18 of 23 as optioned), MSM, 6M, Sunroof, Onyx/Red

2009 G8 GXP, #807 of 1829 (#37 of 68 as optioned), MSM, 6A, Sunroof, Onyx

2016 Chevy SS, Mystic Green, roof, #555 of 2221

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