I found a cylinder 3 misfire code on my civic recently and ran a compression test. Cylinder 1&4 were at around 110 psi and cylinder 2&3 were at about 90 psi. I’m not too sure if I should be driving it like that or even how to fix/diagnose the problem. Any help would be much appreciated.
Do a leak-down test on the cylinders.
I have also have had an oil leak for the past month or two
Recheck the compression by doing a wet test. This means a small squirt of oil into each cylinder before the compression is tested.
If the numbers go up a fair amount then there’s a cylinder issue, Worn/seized rings, scored cylinders, way out of spec cylinders, etc.
If the numbers stay about the same then it’s a cylinder head valve issue. This is quite often due to tight valve lash.
However, given the fact that all 4 cylinders are way down I suspect you have a ring problem and that means bad news.
With all four cylinders having low compression I suspect that either your compression gauge is leaking or inaccurate or the timing belt is off by a few teeth.