Advice after compression test

[rzmoser]

I'm looking for some advice on the health of my m20 after a compression test. I've been thinking about turbocharging it, only to 8psi, but thought I'd do a compression test to see if the engine can even handle it. Its a 325i with 280,000 miles, but was mostly driven by an older women throughout its life. I have receipts going back to 1991 but don't have any record of the engine ever being overhauled. Here are the numbers I got:


1 - 150
2 - 148
3 - 148
4 - 142
5 - 80 (150 with oil)
6 - 150


So it seems the rings are bad on cylinder 5 as the number jumped way up after adding a bit of oil to the cylinder.


The other thing is the spark plus, which looked fine when I adjusted the valves ~8,000 miles ago, but now all have white crust over them. The only thing that's changed since then is I replaced the oxygen sensor. Seems the car is running lean. I've ordered new plugs but would like to get the car running right so I don't foul them too.

[packratbimmer]

#5 rings might be stuck or gummed up. Try doing some hard downshifts (like on an exit ramp)

[jlevie]

It does sound like #5 has bad rings. A leak down test will tell for sure.