After “sending it” at 30psi for a couple hundred miles, I developed a misfire. I narrowed it down to cylinder 3, but wasn’t sure if it was plugs, coils, injectors, etc. I swapped all accessories between cylinders, but nothing would follow. That’s when I started to get worried.
Without wasting any more time, I busted out the compression tester. The results were disappointing.
Cylinder 1: 170 psi
Cylinder 2: 170 psi
Cylinder 3: 80 psi
Cylinder 4: 170 psi
Cylinder 5: 170 psi
Cylinder 6: 170 psi
I’m not sure what exactly caused the problem, but adding a tablespoon of oil down the cylinder boosted compression back up. 99% sure it is a cracked ring or a chipped ringland. If I had to guess, the car developed a misfire but I was too greedy and stayed on the throttle while it was a misfiring for a couple pulls. Or maybe it just randomly gave up… I’ll never know why. The logs looked good before the misfire, but I knew I was playing with fire at this power level.
After saving up for a few months, I bought a used motor from a junkyard. It came out of a 2008 335i 6MT with 91,223 miles. The car was hit pretty hard on the driver’s side, so I’m not worried about flood damage or anything like that. It was also modified, so I’m hoping it was taken care of by an enthusiast.