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Engine Misfire #3

Egleone6

Egleone6

New member
I had posted this earlier, but now it seems to be internal. The compression on the cylyndar was around 60 psi. The other one was 120 - 130. What wouold be the problem? No burnt oil on plug, no leaks or sign of leaks. He mentioned Valves, I am sorta clueless on engines, but this sound EXPEN$$IVE.
 


Pull the front valve cover and look at the springs for #3. Getting 60psi probably means the piston chipped and the rings aren't holding the pressure well, but if a spring is broken that could also allow some pressure to leak out.

Call it a long shot.
 
Billboost is right. Check for cracked or weak valve springs on that cylinder (two middle springs) but make sure the valves are in the closed position before you do this (spring extended). If they are good then it could be a burnt, dirty, bent, or cracked valve. You can check your exhaust valve by removing front exhaust manifold and putting your hand against the exhaust port to seal it while a friend spins the crank with a socket and ratchet and see if you feel air pressure on your hand when valves are closed. if you feel air when valves are closed and motor is being turned. then compression is getting past the exhaust valve. hope this helps!
 
I forgot to mention, its common sense but I'll say it anyways cause it could slip your mind. Its easier to spin a motor without spark plugs but just make sure the plug is on the cylinder your checking or you wont feel any air escaping out the exhaust cause its already coming out the spark hole.
 
Well all I am going by is what the mech has said. He is almost certain that it is a burnt valve. He did a compression test and heard a noise of some kind. He would not know without taking it apart.

Is it safe to say that I am looking at a lot of work? What kinds? Head Rebuild?
 
Hearing air zip past a valve is very normal. Everytime I swap springs on install jobs, there's a few cylinders leaking air. You tap the valve with a rubber mallet and it almost always seals up.

I'd rule out the air sound and go right to visual inspection.
 


yea true but I've diagnosed some bad valves that way. I had a compression reading of 50 p.s.i. that would just stay there. it was about 100 psi short so you can definitely feel a whole lot of pressure and not just hissing, and i agree inspection is always best but its a cheaper thing to do before having to buy a head gaskets set, bolts, and then labor.
 
How do you have a compression gauge with any accuracy that doesn't have a schrader valve in it to hold the highest compression until you press the button and release the pressure?

I mean..yeah if that was the compression, then sure it's low and something is wrong.
 
Just an Update..... All if fixed (fingers crossed) When they did the Compression Test and Leak Test, they all figured, Valve problem. Then this morning they started it up and NO MISFIRE..... Apparently the air dislodged something and is no longer misfiring. I am going to go get a fuel injector cleaning, they said this helps clean the lifters guides and valves. Thanks All.
 
Is it safe to add some tranny fluid (about a 1/2 qt) to the engine? I was told it is used to clean gunk out of the engine. He told me change the oil around 500 miles.
 


Sounds like you might have had a piece carbon between the valve and seat, holding the valve open just a little bit, good for you it dislodged.
 
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