I picked up a 2007 Saturn Ion for scrap money with a bad clutch. I swapped out the clutch and all is well in that department. I pulled a P0304 code from the computer so I started troubleshooting a cylinder 4 misfire. Plugs good, coil good, injector firing. Checked the compression and it's sitting at 50psi. Other three cylinders are good. Drop a bit of oil down the spark plug hole and get about 52psi so I'm guessing it's a valve. What I don't understand is how well this thing is running. It's a basic 2.2l Ecotec. The idle is smooth and it pulls well for what it is. Every time I've had a cylinder that was this low the engine was shaking like crazy and chuffing out the exhaust. It just seems weird.
I can pick up a low mileage used engine, with warranty, for around $300 so it probably isn't worth my while to pull the head and investigate but I'll likely do it anyway.