I have a 2004 A6 2.7t with approx 110k miles. Runs great, no issues. I pull an enclosed 10 ft trailer on occasion (very lightly loaded) and it does fine. The issue is that when on a slight uphill grade, I feel what is like detonation/hesitation. This is most pronounced when in top gear. If I give it enough gas to down-shift, it is less noticeable and sometimes not noticeable at all. Same thing if I manually down-shift it. I admit that I am running regular octane in it and not premium. Could it be that this is detonation? FYI, it does it even in the winter when it is nice and cold. I also noticed this same thing on one specific uphill stretch that I traveled a lot without pulling a trailer. It was a long gradual incline, not enough to make it down-shift though.

I guess I can fill up with premium before my next towing day and see if it makes a difference but wanted to know if anyone else experienced the same.

Along this subject, should I be towing in regular drive or in sport mode?

Thanks for any info.

 

with towing I would be more concerned about your transmission.

I think you are on the right track with using lower octane fuel. this might be something that your car does more regularly than you think, just more noticable when the engine is under a higher load. Your engine is factory tuned for 91 octane fuel. The car's computer system will compensate for use of a lower octane fuel by adjusting the engine timing profile. If you are using 87 octane it is likely that you have gone beyond the limits of what the system is capable of adjusting for. (that makes much more sense in my head than it does when I try to articulate it in words).

I don't think it makes a big difference towing in sport as opposed to drive. Sport mode, as I understand it, just holds the transmission in gear at higher RPMs, possibly putting more stress on the trans when towing.

 

High octane only. Or, better yet, buy a truck. You are using the wrong tool for the job.

 

This. Any turbo engine, let alone one as temperamental as the 2.7T, should run only premium fuel. 87 octane bongwater is bad for numerous reasons. If the extra $.20 per gallon is too high a price to pay, sell the car. Don't run crappy gas in that engine. You'll hate your life later when issues arise.