[s-cars] Detonation - I think

[Tom Green]

> In the last issue, Bill commented:

> From: William Noland <wenoland at pacbell.net>
> To: s-car-list at audifans.com, richard at tanimuras.com
> Subject: [s-cars] Re: Detonation - I think
>
> Yep, sounds like knocking. Could be bad gas. Perhaps, you could live in
> California, which = bad gas. Other thing to consider, if the motor has
> some miles on it, is carbon build up. Eventually, enough carbon will
> buid up in the combustion chamber to raise the compression ratio
> slightly. Given that the the compression ratio is already high for a
> turbo motor, it doesn't take much to push it over the edge. A "carbon
> wash" can be done with the motor and everything in place. I've had it
> done on high compression, normally aspirated, high mileage motors with
> good results.
>
> Your knock sensors will avoid any major engine damage, in the short
> run,
> so not to worry.
>
> Bill Noland
>
>
>> I am getting a rattling sound like dried peas being poured onto the
>> floor -
>> when there is some load on the engine (4th and 5th gears, from half
>> to WO
>> throttle). If I back off throttle, the sound disappears. As long as I
>> use a
>> light foot, there is no rattling sound. This is a first for me but it
>> sounds
>> like the way I have heard detonation described.
>>
>> This is something that has popped up today and I can't think of
>> anything
>> except something restricting fuel flow or low fuel pressure.
>>
>> 1. Can this be anything other than detonation?
>>
>> 2. How can I check flow? How much fuel pressure should I be seeing?
>>
>>
>> Worried,
>>
>> Rich

I would sure check to make sure the knock sensors are operating--pull
codes at least.  What I surmise from the write-up is prolonged rattling
on acceleration.  If it is detonation, doesn't jibe with a properly
operating anti-knock system.

Tom '95 S6