KeithM

I recently purchased a 97 A8 4.2Q with over 100000 miles on it. I am loving this car more and more each day. The only problem I am having is with the gasoline I purchase. Back in November, while traveling for business, I was forced to get gas at what I thought was a semi-shady gas station. I filled up with 93 octane. After 90+ miles on the hwy, I heard a chirping noise when I accelerated (around 35-45 mph)and when coming to a stop. That later tuned into a clicking noise. I assumed it was just bad gasoline.(The same noise occurs on my Explorer if I buy a lower grade gasoline.) It took a couple of cycles of new gas before the noise stopped. I told myself that I would be more aware of where I purchased gasoline.
A couple of weeks ago I went to a BP/Amaco that I had never been before, and the noise began again.

My question is that are A8's that sensitive when it comes to quality/brands of gasoline, even at a 93 octane? Are there any kind of injection cleaning or adjustments that can be done to make it less sensitive? Is this the right diagnosis?

Thanks in advance for any insight.

docmusolf

I use BP gas every fill up and have no problems.

Brent

ryoung

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My anecdote: I once had a car that would develop the same symptoms and assumed it was caused by carbon build-up on the tops of the pistons. The carbon can glow incondescent and cause preignition/pinging just like like low octane gas. My solution was to find a long uphill grade and run the motor to redline in each gear to blow out the carbon. I don't know how much this really helped, but I enjoyed the fix.

High quality premium gas should have enough detergents to clean this out eventually on it's own. Also, some fuel injection system cleaners that you add to a tank of gas claim they address this issue.

Egil A64.2s - S6

Get a can of engine cleaner and add it to a full tank of gas. May just be carbon build up.

skiracer

Randy- that's called an "Italian Tuneup".....;-D

ryoung

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Amazing how expectations have changed -- that car had 58 HP (from 903 cc).

gdaniel

It would be interesting to know what is chirping, especially if its caused by "bad" gasoline. Knocking (predetonation) occurs under load when the octane is too low, not when slowing down. Audis have knock sensors, so when knock is detected the engine control module readjusts the timing curve to eliminate the knock. You just get less power. Any comments?
Gary