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1999 Vortec 4.3L Dead #1 Cylinder


SIP-Rich

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My motor has intermitent mis fire under acceleration as a dead spudder. Idles with a dead spudder. Gets worst right after the tranny up-shifts durning low speed load. Sometimes is ok for a second or two during light throttle/higher rpm's in 1st or 2nd gear. All those problems lead me to think it was spark plug.

 

So far I have changed all plugs, cap, rotor, and wires. Problem is still there. #1 cylinder is warm to the touch vrs all other 5 being hot.

 

The only code the ecu has thrown is a random misfire code.

 

Any ideas?? I am about to do a compression check on that cylinder.

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compression checking one cylinder is a good idea, but what then would you have to compare it to?

 

newer tune up parts? whats the plug look like? how does it compare to the other plugs?

whats fuel pressure?

 

possible injector issue, tune up, maybe compression. but realy lets start with the basic's and go from there.

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Not looking good on the compression. Only 25 lbs, Most others are 125 psi

 

Thinking intake valve.

 

Not poping out of the intake like a exhaust valve would, but I can feel the air going in and out of the compression tester hose. So me thinks maybe the intake valve is not opening and the piston is drawing the air in and out of the exhaust valve. Goingto pop off the valve cover now and see whats what.

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it probably has a bad intake gasket

 

this too. or yet sounds of injector trouble(clogged nozzle's maybe).

 

check for vacuum leaks around the base of the intake, see if you see coolant leaking out of any of the ends etc.

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this too. or yet sounds of injector trouble(clogged nozzle's maybe).

 

check for vacuum leaks around the base of the intake, see if you see coolant leaking out of any of the ends etc.

 

 

It is the 25 lbs of compression in the #1 cylinder that has me worried most.

 

No coolent leaks. I took the valve cover off and both valves/rockers are working normal. I was hoping it was somthing simple like a broken intake rocker/stud. but everthing is fine there. I think I am getting fuel through that cylinder as i could see the wettness on the plug one time I turned it over without the plug wire attached.

 

Wish I had a camera to scope into the plug hole.

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sounds like a burnt valve. you can blow air into the cylinder, i like to do it with the rocker loose so know 100% that the valves are closed. this will tell you if its intake, exhaust or rings. chances are though its a burnt valve.
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sounds like a burnt valve. you can blow air into the cylinder, i like to do it with the rocker loose so know 100% that the valves are closed. this will tell you if its intake, exhaust or rings. chances are though its a burnt valve.

 

yep..if you only have 25 psi...start here

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Looks like it maybe an intake valve. I pumped compressed air into the cylinder with the compression check hose and could hear lots of air exiting the throttle body. Pitch would change if I touched the gas pedal. Looks like I might be pulling the head off.

 

Just for shits and giggles, I pumped a few ozs of oil into the cylinder and turned the motor over once or twice. Rechecked the compression and it went up to 35 psi. So I am going to rule out rings. The motor did not smoke even a tiny bit during driving with the problem. This is going to be a bitch pulling this head out of my wife's astro van.

 

Thanks everyone who pitched me some advice.

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