Compression test results, still confused

[supermailman]

Passenger side bank:
Cylinder 2: 150
Cylinder 4: 160
Cylinder 6: 150
Cylinder 8: 140

Driver side bank:
Cylinder 1: 120
Cylinder 3: 155
Cylinder 5: 155
Cylinder 7: 160

Truck has 200k miles, I am assuming engine is original. Something is seeping out between the head and exhaust manifold around cylinder 3 & 5. Looks like water. Getting a non stop code 45 and that side's exhaust is smokier than the passenger side (true duals). Converted to heated o2 sensor. Just replaced intake manifold gaskets and exhaust manifold gaskets, still leaking at the same spot. Truck already got a complete tune up with plugs, wires, cap, rotor, coolant temp sensor, TPS, MAP sensor...the whole shebang.

So I guess the real question is, what is going on with cylinder #1?

 

[kennythewelder]

Vortec I assume, Vortec heads are prone to cracking. The only way to know for sure, is to pull the heads and have them checked. Could also be a bad head gasket. If you do pull them, and take them to an automotive machine shop ( the only way to know for sure if there are good) and they are bad, that would be a good time to upgrade to a high set of performance heads. The aftermarket vortec heads, are a thicker casting that the OE heads are.

 

[supermailman]

Sorry I forgot to include that this is a TBI 350 motor. I'm not getting any coolant mixed with oil yet so I was really trying to convince myself it wasn't the head gasket lol. Local machine shop wants $200 plus parts to clean/check/rebuild the heads. I am not looking to spend a ton of money on an engine with 200k on it so new heads would probably be a no go.

 

[slowburb]

Is it drinking coolant? I don't know OBDI. What does the code mean? Low compression could be what kenny suggested or in the valvetrain...like maybe a valve sealing issue.

 

[evilunclegrimace]

Run a leak down test.

 

[90halfton]

I would make certain of what is leaking. Smoking could be valve guide seals, they are notoriously terrible, usually not all the time though, unless they're super shot.

 

[east302]

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[c1500deathtrap]

Run your cylinder to TDC on compression, (both valves closed) then use your adapter for the compression tester and hook it to a compressor. Run 20ish psi into it. then listen for where the compression is going. Bad intake valves will make a hissing in the intake, exhaust out the tailpipe, or rings will be in the oil pan.

 

[Ken K]

You can do a "Running" compression test. A static test is the best place to start, but with those numbers, you are outside the maximum 10% or each other. I have a SnapOn cylinder leakage tester, but you can make do.
The cylinder fills with the most air at cranking speed. The faster the engine goes, the lower compression is because of volumetric efficiency. Ground the plug wire, leave the compression gauge in one cylinder and start it up. Release the pressure and note the new reading. It will be lower, but help you get additional information to help decide where the problem is. If a valve guide is worn, the reading will be lower. Don't forget a wet reading using oil. Squirt a couple of shots of oil into the cylinder, turn over with coil & fuel pump relay/fuse disconnected, about 3 times. Install gauge and retry.
Otherwise, I agree as a leakage test is best. Note; if fuel is still coming in, it will wash the cylinders and give you false readings, lower than normal. Good luck.

Retired ASE Master Tech.

 

[kennythewelder]

You can do a "Running" compression test. A static test is the best place to start, but with those numbers, you are outside the maximum 10% or each other. I have a SnapOn cylinder leakage tester, but you can make do.
The cylinder fills with the most air at cranking speed. The faster the engine goes, the lower compression is because of volumetric efficiency. Ground the plug wire, leave the compression gauge in one cylinder and start it up. Release the pressure and note the new reading. It will be lower, but help you get additional information to help decide where the problem is. If a valve guide is worn, the reading will be lower. Don't forget a wet reading using oil. Squirt a couple of shots of oil into the cylinder, turn over with coil & fuel pump relay/fuse disconnected, about 3 times. Install gauge and retry.
Otherwise, I agree as a leakage test is best. Note; if fuel is still coming in, it will wash the cylinders and give you false readings, lower than normal. Good luck.

Retired ASE Master Tech.

X2 nice write up Ken