In Reply to: More valve problems posted by Chris Rose on September 27, 2001 at 20:25:32:
Never heard of valve pinging before (lifter noise yes, but we'll get there later)
You got two different noises here:
1) Lifter noises (valve tapping on valve stem)
2) Engine knock (preignition)
You will/may hear lifter noises at idle, but not pat 2k rpm. The knock sensor will not do anything for lifter noises. Don't recall the valve adjustment on the 525, but if it's like the 535, it's time to adjust the rockers (whick would tap against the valve stem making the noise).
2) Engine knock IS controlled by the knock sensors and gets reduced by adjusting the engine timing on the fly. Engine knock occurs for a number of reasons (heavy carbon build up in the cylinder pre igniting, bad gas, early detonation, etc). Engine knock does not happen at idle; but under load (normally higher than average load). You normally would not hear it driving down the road until you reached a hill and the engine got more load. Now, you normally shouldn't here this either because the knock control will retard the timing to reduce/eliminate the knock.
So, the question(s) are:
1) Does the noise tend to happen at idle? If so, I'd look to valve lash adjustment
2) If it happens under load, I'd suspect you have a problem with the knock sensor. Is the noise more pronounced when you accelerate hard? May be something as simple as the connector coming undone.
3) IIRC, the rotten egg smell has to do with the cat. If you are running rich, I'd check the spark plugs to make sure none are fouled. When/did you change plugs?
4) How do you like the stethoscope?
I posted a few weeks ago that I was hearing a valve taping coming from my '95 525 at idle. It would come and go. Almost like once it got loud enough, the anti-knock system would kick-in and reduce it. Then it would start getting louder again.
Anyway, the tapping is pretty much quieted down now (I can still hear it a little, and more so with the stethoscope of course). However, now I'm getting some valve pinging when driving the car. I've got 93 octane in it and I still get some minor pinging.
Also when I pull in the garage, I notice a "rotton egg" smell. Like maybe the car is running rich.
Can anyone put all of these clue's together? I'll probably take it to the dealer next week I guess.