I recently took my 2008 3.2 Q7 to the nearest dealership for a bit of warranty work. One of the problems I was having was that on more than one occasion, the engine seemed to miss. Once it happened at very low speeds driving through a neighborhood. I actually thought it was going to die, and gave it a little gas to get it going. The other time was accelerating on a freeway on-ramp.

Anyway, I explained this to the dealership, and after testing, they told me they believe it was the result of low quality fuel. They said that the Audi's computer recognized misfiring on two occasions. But the strange thing was that all 6 cylinders misfired at the same time, I guess which is why they believe that it was the result of bad fuel.

I guess I should preface this by saying I really know nothing about cars, I'm simply repeating what I was told. As far as the gas goes, I've always put 91 octane in it, even thought I was told by several people that it didn't make any difference. Also, I almost religiously get my fuel from the local Safeway that also has a gas station. It is literally right around the corner from my house, so I shop there for groceries, and get gas there because of the large discounts they give customers. So it makes sense to me that it could be simply bad gas. My wife has also noticed issues with our brand new Ford F-150 with the Eco-Boost engine, and she too always gets gas at the local Safeway.

But researching online, all I see are opinions that gas is the same from brand to brand, and that it doesn't matter which you use.

So am I just being misled by the dealership? The bad gas theory seems to makes sense to me. And I would think that they would try and make as many repairs as possible, since it would be warranty work they would be getting paid for.

So has anyone else had problems with gas that wasn't from a major brand like Chevron, Shell, etc.?

 

my former vw 1.8T and now audi TT 225Q run best on Shell 93 octane, they were both "chipped" for 93 oct programs, if you car calls for regular, midgrade is a good choice, our modern 10% ethanol SUX!! stick with top tier gasses, no name fuels only have minimum addatives

 

Ive had about 13 cars in my lifetime (so far) and on 2 occassions I had cars act like crap when I bought gas from a certain station. Each time the car ran horribly after going down to about 1/4 tank. I stick to shell and 76 now. In a pinch I will use chevron because I never had an issue there either.

Does it do it once then not again for a long while?

 

You should always try to use fuel (premium for a 3.2L) that's on the "Top Tier" list. However, with these (and all direct injected gasoline engines) the problem is the cumulative build up of deposits on the intake valves. Because there's only air and oil vapor (from the crankcase ventilation system) on the back of the valves, it builds up over time. There's no fuel being sprayed on them to keep them clean. Not just an Audi thing, by the way. Originally we would take the intake off, use combustion chamber cleaner and brushes to disolve the deposits and then ssuck them out of the port (valves closed when doing this, obviously). Have been having good luck doing a Wynn's Induction System service (3 step process). This eliminates removing the intake AND saves our customers a bunch of money.
We do recommend to have it done every 20,000 miles or so after that as a maintenance.

Sign of the times. Direct injection equals better performance, using less fuel and producing fewer emissions. Downside is intake valve deposits and the resulting misfires that are either felt by the driver or just detected by the ECM. In other words, what needs to be done is modify scheduled mainenance services to reflect it. Yes, an additional service to pay for BUT other service is either not needed anymore or not as often as they used to be so, it all evens out. Not MORE service, just DIFFERENT service.

By the way, warranty doesn't work the way most people think. If we cannot backup a repair with proof it was needed AND the customer had a concern, the claim will get denied. Plus, and this has nothing to do with the customer, warranty labor times usually are less than it actually takes to do the job properly. Don't forget, we technician's are paid on flat-rate so we tend get in too much of a hurry sometimes on a warranty ticket. I mean, we want to resolve the concern and make the customer happy but at the same time, we also have to pay the mortgage

 

its unfortunate of the costly issues direct injection cause, rumor has it an xtra injector may be added working the old standard way, one or more cars are already using this setup, its outragous that we have to pay for this design flaw, an xtra cost for sure but necessary to control deposits, other manufacturers have stayed away from DI for this issue despite its many good points. at todays cost for a car manufacturers should be held responsible for this issue!!

 

As a person that has obviously been in Engineering too long and over-thinks everything.. here is my two cents on this thread:
In "my area" I find that if I buy gas at Holiday I observe poor performance, hesitations on acceleration, and poor mileage. If I buy my gas at Super America: everything seems to run better (starts better, higher mileage, no hesitations on initial acceleration). These differences were obvious with a study on my resultant gas mileage..typically a loss of 3-5 miles/gal not to mention what may be happening internally in my engine (build up from from the retardation of ignition timing and the unintentional effects of a combustion cycle that was not designed or intended for my vehicle).
Here was my first clue: I frequently travel up to northern Wisconsin and Minnesota.. were I travel to there are no Super Americas available; only Holiday stores. When I gas up in these areas I see NO LOSS OF POWER OR FUEL CONSUMPTION.. what's the difference you may ask; The amount of fuel consumed by those stations! When I got home, I emailed the owners of the two stations near my house and I found that the Holiday station sold an average of 800-1100 gallons of gas a day; the SA: 2200-2700 a day.. that is a huge difference and because of the higher consumption at the SA, they had larger tanks and received gas from the distributor more frequently. The quality of the gas is quite standardized at the federal and state level to insure that the advertised quality and specifications of the gas from the refinery meets the knock equivalent and purity required by law. As with any Petroleum product: gas does absorb water and will degrade based on how it's stored, how long it's stored and the quality of the holding tanks. So in my opinion "YES" where you get your gas does matter.
Side note: On my 2005 A6 3.2 the difference in mileage (and performance) that I receive running premium vs. 89 octane pays the difference in the price at the pump.