Engine problem

brandonsmith

i have a 2001 Pontiac Aztek and it has a cylinder 6 misfire. So I did a compression test and cylinder 6 had 90lbs, but I then tested cylinder 2 and 4 and they both had less than 20lbs. I'm not sure if it's the head gasket or head warpage or a cracked head or block. Or even something else

Mr_Shiftright

I'm surprised the vehicle even runs. There's no way to tell what's up just from a simple compression test. What you should have is a cylinder leakdown test to narrow the source of the problem (pumping compressed air into each cylinder and measuring the % of leakage of the air over a specified amount of time and perhaps where the leak is occuring---valves, head gasket or engine bottom end). Once you've verified significant leakdown in one or more cylinders you'll have to pull the heads off.

Another way to test for head gasket leaks only is to pressurize the cooling system with a pump and while still under pressure, remove the spark plugs one by one. If you see coolant on the tips of any plug, then there you go--head gasket or maybe cracked head.

Another method for head gasket detection is to buy a chemical test kit that can test for combustion gases in the radiator coolant. This wouldn't tell you anything about the valves, or whether the cause is the head gasket, cracked head or warped head.

Why did you mention warpage? Has the car overheated badly recently?