cylinder firing issue

staplerplease

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2007 Pontiac g6 4 cylinder, number three not firing, replaced plugs, swapped around, checked swapped coils, check and verified good wiring, checked and swapped fuel injectors/checked wiring for them as well, issue stays with the same cylinder, checked the piston heads, the ones that work have a bit of carbon, to be expected, but the third one is wet with a lot of carbon, could the intake be dirty enough to cause this issue ?
 

melsg5

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It's strange you dont have P0403, you are sure you reader is working?
You have do a compression test.
Does the number 3 spark plug look different?
If you have no check engine light what made you start looking for an engine problem?
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staplerplease

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the engine was running like crap, so I checked all the obvious possible issues, the problem just follows that one cylinder, and that is the only cylinder that has a lot of carbon and wetness, I assume that is the problem.
 

melsg5

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are you going to do a compression test?
does your check engine light come on briefly when you start the car?
 

melsg5

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you can rent the tool
have you checked for blown fuses, especially the cigarette lighter fuse in the rear compartment fuse box, OBDII port is usually powered by that fuse.
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staplerplease

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ok, I did the compression test the cylinders that do work read about 90 at most, the third cylinder giving me issues is reading nothing, I removed the intake and throttle body, the O-rings are bad hard and dry rotting, where the seals touch the engine it's all full of dirt and fuel, rings are flat, so I know it's sucking in air. could that be the problem ?
 

melsg5

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did you have the throttle wide open when you did this compression test?
the 90 psi is extremely low and the zero is a dead cylinder pointing to probably valves.
was this engine noisey, timing chain clatter, before it started to run rough?
 

staplerplease

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the way I was told and according to the tools instructions, I was to disconnect the coils, do the test one cylinder at a time with the plugs out and crank the engine for four turns while watching the gauge, 1,2 and 4 hit about 90 and 3 was trying to move.
 

melsg5

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not sure why the instructions didnt tell you to have the throttle wide open but you have a dead cylinder and need to try a wet test to see if you have a valve problem or rings but unless you broke a ring it's probably the valves.
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staplerplease

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that's kinda what I was thinking. the car was given to me from a friend that was tired of messing with it, been sitting for a while. it needs a good cleaning anyways, I got a head gasket kit, just going to rebuild it, small 4 cylinder anyhow not that complicated. just didn't want to have to get that deep into it. plus this winter air makes it hard to get to.
 

melsg5

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not clear on your question, as of yesterday you hadnt removed the head and I would assume you are sending it to a machine shop for a valve job?
 

staplerplease

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i'll be doing the work myself, I just need the valve lash adjustments. can't seem to find that info.
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melsg5

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perhaps you should find a manual, Hanes, etc. to help you before you make a mistake. The engine has hydraulic lifters.
 

staplerplease

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well update on the head job, have it all torn down and the head gasket is leaking oil and one of the exhaust valves on the third cylinder is worn, one side looks like it was shaped oblonged , leaving a nice gap into the chamber, and the rest of the valves are all full of carbon,other than that everything else looks good. and the exhaust manifold has a crack down the middle.
 
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