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99 Posts
Discussion Starter · #1 ·
alright guys heres my situation... 2004 6 v6. 43000 miles on her. she has been using some oil. about a quart and a half ever 3500 miles. today she blew a CEL P0304 which as most know is the cyliner 4 misfire. I cleared the code and now im gonna see if it comes back or not. but i just wanted to get a thread started on it. my mods are cpe cai and magnaflow catback. i also am only getting about 13-14 mpg on average. i know i have a heavy foot but before i deployed i was getting 16-22.

1. Type of oil & filter used-ive been using gtx 5-20wt and a british brand oil filter...Yes its an american spec 6.
2. Oil change intervals-3000-3500ish
3. Type of Gas used-93 octane i believe is what they have here on base
4. Last time when you changed the spark plugs-havent.
5. Last time when you changed the coil(s)-havent.
6. Mostly highway or mostly city driving?50/50
7. Ever had any rocks or pebbles hit the undercarriage? no but i have bottomed out a few times since im lowered 3 inches
8. Any misfire history? How long did that last before you got it resolved?-not that i have reconized
9. mpg-.......13-16
10. Any loss of power experienced in the last 6 months or so? none

all i know is im about to be pcsing to texas from the uk and she will be loaded on a ship in about 2 weeks so i need to do what ever i can before she goes.

· Registered
228 Posts
If I were you, I would change your spark plugs AND coils. I would also change your PCV valve and hose. These basically all require the same steps to get to, so once you get to your spark plugs, the PCV valve takes 2 seconds to change, and the back 3 plugs take a little work to get to, so that's why I recommend replacing all your coils while you are back there. Misfires will destroy your engine by breaking up the pre-cats, so I would get this taken care of right away and not drive it anymore. I recommend going to and purchase the standard products coils (~$35 each). I would go to your local auto store and get the NGK spark plugs (~$7 each). You can also order the PCV valve from (~$10), and just buy some hose from your local auto store and cut to fit to replace the existing hose. Total cost is around $300 or so. Don't forget antiseeze for your spark plugs. Total time to do the job if you have never done it, is around 3 hours taking your time and going slow.
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