To the best of remembrance to my mechanic days, this is how I know gasoline works; First octane rating, most gas you’ll find (in the states) is anywhere from 87 to 93 with the exception of E85 branded fuels. The higher the octane rating, the slower the fuel actually burns. Recreational or power equipment is usually air cooled and those engines can reach a higher temp so the higher octane rating keeps the fuel from pre-igniting before it fully enters the combustion chamber thus preventing knock or ping (on engines that aren’t controlled for it). Most of the time it’s used in Harleys, older engines, engines with higher compression ratios or lawnmowers, etc. The problem that first arose with ethanol blended fuels is that the cars at the time weren’t equipped for ethanol and people were noticing rubber fuel lines and gaskets that were touched by the fuel would actually dry out and crack because the alcohol would absorb moisture from said components and cause premature failure. Manufacturers started compensating by making said parts from materials that could withstand the ethanol and its affects. Most of our cars should not have a problem with that seeing as how that was implemented a while ago. Most newer ecu and efi engines are equipped with knock sensors and robust fuel system components so that if the engine senses knock or ping it can change the timing accordingly to offset the affects of a quicker burning fuel. Ethanol blended fuels should NOT affect our car’s performance, but I’m old school and don’t use it, also because I notice I get a few more miles out of a tank of gas running premium non-ethanol fuel. That’s the second part because it takes more alcohol to equal the property of gasoline. People with flex fuel branded vehicles can fill up with that stuff for less money at the pump, but then they complain that they don’t get as many miles out of a tank of fuel running that stuff (kinda how I notice the extra mileage with premium). The owners manual or fuel door should have a minimum octane rating that is recommended for you car (I believe ours will say 89 or 91, a bit fuzzy from memory). Remember GM cars like cadillacs or gtp pontiacs how the gauge would say “unleaded fuel only, premium recommended”? Usually those models had engines with higher compression hence the premium fuel suggestion.

So to answer an earlier question, no the gas station attendant didn’t really know what they were talking about, ethanol isn’t going to hurt our cars, fill up with whatever the fuel door or manual suggests for an octane rating. Any fuel will work, but these are Audi cars, so I’m trying to do the best I can to make sure mine lasts. I was running 93 octane Shell premium in my car until I noticed they took of the non-ethanol sticker and replaced it with “all fuels may contain 10% ethanol” so now I’m filling up with 91 octane ethanol-free fuel from a different Shell station. That prior station was the only one in my area that had 93 seeing as how it’s becoming a thing of the past and 91 is the max you’ll usually find. Long paragraph, I know, but I wanted to share my take and reasoning as to why I fill up with what I do.

Well I know we’ve wandered off of my original post, but thought I’d give an update on the misfire situation that started this. So I took the car to another dealership in a more metro area for them to take a peek. Left the car, they did more airbag recalls and then did some testing. Took it there with it misfiring and the CEL on, they were only getting a P0301 code. They tested things by moving coil 1 to 3 and 2 to 4 and switching around a couple spark plugs as well. During that process they found that spark plug hole #1 was full of oil. Told him that my local dealer replaced the gaskets back in March and he advised taking it back to them for replacement under warranty due to the fact they were again leaking. In the meantime he told me that after switching things around the misfire stopped, couldn’t tell me why but he was right. I picked the car up and it was butter smooth again, the exhaust sounded better and it was just right, was so happy! Then a couple days later it started acting up again, read the code with VAGCOM and it was the P0301 cylinder #1 again. Dropped it off today at my local dealer with my paperwork from the other one and they replaced the gasket under warranty and told me the plug hole had oil in it again, which was cleaned out while they were in there. So tonight I pick it up after work and during the drive home I noticed that it ran no different from when I dropped it off this morning. Fit to be tied here now. Tried calling the other dealer to update them on the process twice last week and never got a return phone call. So now I’ve been to two dealers, one was on the right track and kinda had something going momentarily and the other one doesn’t seem to give a ****, even though it’s been doing this since their first repair and recall. I know I hate the “ever since you worked on my car...” bit, but it happens. I shared my days as a Harley tech to let them know I wasn’t crazy and being accusational by telling them about my experience. Guy brought in a perfectly running 15 year old bike, did a big bore with cams, exhaust and aftermarket ECM. Everything went together like normal but after I was done and started the bike, it was only running on one of two cylinders. After some cursing I took a step back and did some testing and found that one injector wasn’t working. Never touched it, but I did have to unplug all the wiring on the induction module to remove it for tear down. Found a wire that must’ve been corroded or brittle and it broke inside the coating. Replaced the section of wire and it ran like a top. So yes, that bike was running perfectly until I worked on it, then it ran like **** so I figured out why. Something tells me I think there may be a similar issue going on here. It’s not the coil or plug, but the misfire stays on cylinder #1 with any of the other coils in any position. That’s where my mind goes, but I’m running low on patience, just want it fixed.

Yes I’m running the OEM NGK plugs right from the dealer. They’re platinum or whatever with the standard ground electrode with the two smaller supplemental electrodes. When I first bought the car I gave it a tune up with Denso (I think) iridium IX plugs, but they seemed to create a hard start so I bought new OEM plugs and used those. A year later after the issue I described I bought another set of OEM NGK plugs and coils and nothing changed. That’s what makes me think my problem may lie elsewhere.

Been a bit and hate bringing up old posts, but believe it or not this is still ongoing. Lol. I did notice something that happened twice during all of this, but my brain doesn’t think it should be an issue but ANYTHING can be an issue with these cars. Got on it hard the one night, it spit and sputtered so bad that the car felt like it was dying with the CEL flashing and EPC light on. Limped it to a parking lot, shut it off, started it back up and it was back to normal (not the good normal, but my normal). Drove for a couple weeks and was messing around with the hood open one day while a friend was over. Started the car to back it out and it started running like the night I just described. Ran up to the front while it was running funny looking for anything obvious and noticed a whining sound in the engine bay and saw the low pressure hose from the tank to the HPFP manifold was shaking, so I grabbed it and felt it, and I could feel the whining in that hose. I shut it down and fired it back up and everything was normal-ish again just like that one night. I’m wondering if maybe the in tank fuel pump may be giving me a problem? Like it’s on its way out and it’s not getting quite enough fuel to the lift pumps and it’s running erratic because of that reason. I would think if that were the case I’d have more evenly distributed problems, but anything is possible at this point. I’m planning on picking up a pressure tester/gauge this weekend and I’ll see what the specs are and see if the car is within the parameters.

Also in the meantime I replaced all 8 injectors under the manifold thinking that may cause a misfire too from another vehicle I worked on in the past that was causing a misfire due to a bad injector. Since that big job, the car still runs erratic however I can’t get the CEL to flash even though I used to be able to recreate the condition to do so on a moments notice. The dealership mechanic thought it was funny that he couldn’t recreate it ‘til I said “hop in the passenger seat, hold my beer and watch this.” I’d take it on the highway with him and if you gave it 3/4 throttle and created a load on the engine (not letting it downshift) the light would start flashing. Maybe it wasn’t getting enough fuel? Not sure if the in tank pump can cause that because I think in my head that the lift pumps are forcing fuel in there, but then I think that maybe the lift pumps are starving because the in tank pump might not be keeping up?

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