Detonation on light acceleration

Drove my X to lunch today and happened to be crusing along with the stereo off, since I had gotten a cell phone call earlier. I noticed a fair amount of detonation on moderate acceleration. This is with a 5-speed, 2000 V-6.

Since I haven't been home from work yet to look through the service manual, can someone enlighten me on whether the timing is adjustable or not? I'll probably find out when I get home before I read this, but I'd solicit any other opinions on the matter anyway.

My wife filled the X up with gas the last two times, so the quality of the fuel is unknown at this point, too. I'll ask when I get home. Not sure that the detonation hasn't been there for the past two weeks (since I bought the X) or not.

I believe it is although I don't have a manual available at the moment either. How many miles on your X? Do you know what kind of past servicing it has had? At what speed did it happen and in what gear? By detonation, do you mean engine knock? The reason I ask is maybe you're hearing a diesel-y noise from the infamous cracked manifold problem?

Enough questions for ya?

Just looked through my Chilton's and it shows how to check and adjust the timing.

My X has 35k miles on it. Absolutely no past history on the service. It had pretty dark oil in it, which I changed immediately, and was running low on coolant (can't find any leaks, head gasket's not bad) when I bought it a couple weeks ago.

It is definitely pinging a bit on acceleration, primarily when the A/C is turned on. Sounds like it's just a couple degrees out of tune. I've got a timing light so I can check it later on this week when I get a chance.

Just as an update, I filled the tank with known good gas (at least where I usually buy it) and today heard no pinging on acceleration. That includes hauling 40 landscaping blocks home this evening with the A/C running, climbing the steep grade on our road in 3rd going 35mph.

Guess I had a bum tank of gas. Mileage on last tank was lower than normal, too. I consistently have been getting between 18.3 and 18.9 mpg in town. Last fillup only garnered 17.9 mpg.

Oh, and to make most people sick, I paid $1.299 for gas....