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Discussion Starter #1
Hi, I'm new to the forum.
I have a 2007 pontiac g6, 2.4l. In my opinion, it was a steal at $1300, 130k miles.
I bought this knowing it would have a few small issues needing fixed, one of them being the misfire.
I've replaced all spark plugs and put new ignition coils on the leftmost and rightmost cylinders (not knowing which one was #4) and cleared the codes, which had no effect.
I've been told the fuel injectors could be the culprit, and I've ran fuel injector cleaner through a few times, also no effect.

It may be worth mentioning there is a slight clanking noise when accelerating, most noticeable going on an on-ramp. When I bought the car a month ago, the mpg was 24, now down to a measly 19.1.

What should my next plan of action be, fuel injector replacement?

I apologize for the poor format (tired) and not knowing a whole lot about cars.
 

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I would do a compression test to make sure that the problem is not an internal engine problem like valves. If all cylinders check out then try to isolate the problem cylinder. The number 4 cylinder is on the driver's side but I don't know why that would make any difference. Is the misfire constant or does is happen under load ? Clanking ???
 

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Discussion Starter #3
Thanks, I will definitely check on getting the tools for the compression test. As far as I know, the misfiring is constant, the mpg always stays about the same, even on long rides. And the clanking I was talking about, I probably should've described it as ticking. Still pretty concerning, tho. I can try getting an audio recording of it within a few hours.
 

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Discussion Starter #4
Update - New fuel injector on driver side, no difference. I did forget to mention I do know for sure a valve cover gasket is bad due to oil on spark plugs. Could this be related to or cause the misfire? And are you sure cylinder 4 is the driver side?
 

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Discussion Starter #6
Honestly, I don't recall. It's been two weeks since I've replaced them. Not quite sure what you mean by external part, but one was so bad it was dripping. There's already darkening on some of the threads of the plugs, last time I checked.
 

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The spark plug threads into the cylinder head. The part inside the combustion chamber is where the spark occurs between the tip and ground. The part outside is the part you can see after you screw it in, i.e. the porcelain and end metal piece.
If you have oil dripping on any part of your spark plugs, that's not a good thing as they could shortand cause misfire. Fix this known problem first.
 

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Discussion Starter #8
I have a buddy that will hopefully help me out with it tomorrow. The oil leak is slow enough where it hasn't shorted anything out yet.
 

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On an inline 4 cylinder engine, the number 1 cylinder is located at the end of the engine with the drive belts and generator, AC compressor, etc. So, the number 4 cylinder is on the other end. Do you have a scanner telling you that there is a problem with the number 4 cylinder ? Is the spark plug well filling up with oil. ? A new valve cover gasket set will include gaskets for the spark plug wells.
 

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Discussion Starter #10
Yes, I have a $20 walmart scanner lol. And some of the wells did have oil in them when I was switching them out. I already have the gaskets, I'm just waiting for someone with more experience to help me out. I've actually just recently gotten a new code, a lean fuel mixture one. I'm seriously hoping the engine isn't shot. The chattering I mentioned before is concerning.
 

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If the scanner is giving trouble code numbers, go online for a good explanation and fix suggestions . Is it saying a lean fuel mixture for cylinder 4 ? If you pull the cam cover for replacing the gaskets, check the timing chain.
 

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Discussion Starter #13
Well, the lean code isn't actually cylinder specific. And it always comes on after the misfire code, leading me to believe it's a result of thr misfire.
 

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Maybe that's pointing at a fuel injector problem. I will be interested to hear what your friend thinks about the situation.
 

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Discussion Starter #15
Fuel injectors have already been replaced.
Compression results are:
1-170psi
2-165psi
3-105psi
4-100psi
 

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Are those wet or dry readings ? Add a bit of motor oil thru the spark plug hole for "wet" readings. If the readings improve it means there is a piston ring problem. If they stay pretty much the same, the problem is strictly the valves. I'm not sure if those numbers would cause a misfire for that engine though. I'm not an expert here.
 

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Discussion Starter #17
It was a dry reading. I won't be able to get the compression tool again until tomorrow. I've heard a variance of about 10% is acceptable, so I'm quite off. I'm probably just going to have to put a new engine in it somehow. 😡
 

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To bad the auto repair is a thug industry because if the problem is just valves the repair is not all that difficult for an inline 4 cyl. The engine doesn't have to be removed to do head work.
 

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Discussion Starter #19
Update: spoke to a mechanic
Given that I'm not burning oil or losing coolant, his opinion of the compression and misfire problems was the result of the head gasket being blown between cyl 3 and 4, ableit an odd spot. He observed the engine would idle rough in a pattern, following the firing order. He pretty much said the compression would be leaking from one cylinder into to the other through a crack in the gasket. And as for the sound, he said the lifters are notorious for that in these engines (idk what those are.)

Anyway, I used to go to a technical school which had a car shop in it, and may be able to get the piston rings etc inspected to see which parts are bad, free of charge. I'll keep updating as i learn more.
 

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A bad head gasket sounds like a good analysis. The 2.4 inline four uses hydraulic roller tappets which are pretty quiet on my G6 at least. Far quieter than my Honda Prelude. What these engines are known for is noisy cam drive chains and their guides. That's just my impression though.
 
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