1997 BMW 528 Repair Question
BMW 528 Compression Problem
A fuel pump will quit unexpectedly, and while a loose wire will cause that, the pump motor itself is more likely to be the cause of that. You won't have any pressure at the test port on the engine. You know changing the spark plugs is not the answer because all four, six, or eight of them are not going to foul at the same time. A bad plug will cause a misfire, possibly an intermittent one.
A more common cause of sudden stalling is a failing sensor. In particular camshaft position sensors and crankshaft position sensors often fail when they get hot, then work again when they cool down. This typically happens when restarting a hot engine that has been off for a few minutes. The heat has a chance to migrate up to the sensors when there's no natural air flow to cool them.
There really isn't much you can do to cause a sudden loss of compression. The best I can imagine is the timing belt was about to jump a tooth or break and you put in spark plus with too long a reach and locked up a piston. The problem with that theory is your engine uses a timing chain, not a belt. I'm more inclined to think you do not have a loss of compression, but some other symptom and cause. To be sure, use a compression tester to test one of the cylinders.
Check for spark too while a helper cranks the engine.
17,287 answers provided