Dads Toy

I have a 1999 Suburban with a 5.7L V8 (144,000). Leaks no oil, uses no oil, has no coolant leaks. Problem I have is cyclinders 6 and 4 have only 10psi on a compressing test. It starts on a dime with no problems and idles with a bad miss. If you go up a small hill or load the engine it knocks bad. Just wonder if a bad intake Gasket could cuase this or is it more leading to a head gasket repair? Spark plugs are dry and have no oil etc, clean burning plugs. There is no oil in the coolant, oil is fine.

kevinkpk

Any blowby in the crankcase?

Dads Toy

How can you tell?

kevinkpk

Pull the oil fill cap off, is it excessive? That is blowing oil mist heavily out the oil fill port.

MDTAHOE

Blown intake gasket will not cause low compression. You could be looking at a head problem but that would be rare on a 5.7. Try adding some oil to the cylinder spin it over a few times and see if compression go up. It could be possible that the fuel injection unit has failed and washed out the cylinders

maxxman04

i've had two vortecs that blew the seal between cylinders. cylinders 4 and 6 as well as 3 and 5 have the exhaust valves side by side. this is where i've seen the head gasket fail, directly between these cylinders. the water jackets stay sealed, so no coolant leaks, but compression is lost.

73shark

Rings and valves can also cause low compression. If oil in the cylinder doesn't help then try hooking an air line to the cylinder and listen in the intake and tail pipe for air hiss.

Dads Toy

That's a great Idea. I can use my compression tester since it already has an air fitting on it. I just wonder if a fuel injector can pop out?

maxxman04

no, they locked in pretty good.

MDTAHOE

On the 5.7 with CPI injection the fuel injectors can pop out. They snap into a small hole with a plastic tab. Over time the plastic tab breaks off an d injector pops up away frao the hole.