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Old 09-16-2002, 07:42 PM
ROGER E. ROGER E. is offline
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Join Date: Sep 2002
Location: SEATTLE
Posts: 239
V-6 startup knocks

What's wrong with this picture?

Nothing at all. I described very clearly what this sound compares to in my first post:

"My 2001 C-320's engine has produced a knock-knock-knock-knock (presumably until oil pressure comes up) on 90% of it's engine starts since it was new. Hot or cold, makes no difference. This is the same sound one hears during the first start after an oil change until pressure comes up. My '95 C280 did this (it had an oil pressure gauge, unlike the C320) so I know that it quieted down as soon as pressure was seen on the gauge and was not heard again until the next oil change."

Seems to me that anyone who has been doing his own oil changes would be familiar with this sound. I certainly am and I'm not even in the business. And the suggestion that it might be detonation:

<<1. Knocking, as it detonation, is handled by the "knock sensors" that your car is equipped with. It automatically retards the timing to get rid of the knock. If detonation is indeed your problem, you'll need to try higher/different octane gasoline. Our 190E 2.6 HATES a certain brand of gasoline, and I found out it's high in sulfer and they often "fudge" octane ratings.>>

I know the difference between pinging and knocking and it's considerable.

The suggestion that it might be the AC clutch might lead me onto the right path except that these compressors have no AC clutch since they are swashplate compressors and are turning all the time even with AC off. But, since I'm getting nowhere here, I'm going to turn the HVAC system completely off for the next ten starts or so to rule out something in the compressor.
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