B6 S4 throttle hesitation, occasional no-starts, gas pump shutoff...

[notasausage]

After 2 years of ownership, it's time to track down and fix what I believe is a fuel issue with our 2004 S4 Avant. A few things that may or may not be related:

• Refueling causes gas pump to automatically shut off as if it's full already, requiring some play with the nozzle to fill the car with gas (usually turning the pump handle upside down)
• Car hesitates on throttle, especially through turns
• Occasionally does not start on first few tries but eventually turns over with fuel hesitation
• Feels like it should accelerate faster

The gas pump shutoff has been happening since we bought the car, and likely could be a leak in the EVAP system or a bad charcoal canister. I've also been told these issues could be due to a bad fuel pump or fuel filter. After some research online (including these forums), I'm not sure what my next steps are. Ever since we got this car home, I've really enjoyed driving it but something tells me it should be faster, as if the engine isn't getting enough fuel.

I have a VAGCOM HEX II cable and a laptop with VCDS, and I've done an autoscan which didn't turn up any obvious culprits. Are there any specific tests I can do with it to track down the problem(s)? Thanks in advance...

[VinnysS4]

From my past experience:
When someone "tops" off the gas, it can fill the charcoal canister and can cause the clicking off nonstop issue. I believe it "clogs"the evap vent and causes this condition

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[Lucca M]

Start with fuel filter as it has pressure regulator built in. If that doesnt help then check fuel pumps and relays.

[VinnysS4]

Start with fuel filter as it has pressure regulator built in. If that doesnt help then check fuel pumps and relays.

I second this. We have a four bar system and so if you check the pressure at the rail with a T fitting it will bounce up and down (with each injector firing and the fuel rails repressurizing) but you should have 4 bar of pressure KOEOff and about that KOEOn. The filter is a good maintenance item, and don't cheap out. It literally houses the pressure regulator.

When someone says their car feels like it should be faster, 2 things come to mind.
Intake flapper and exhaust restriction.

If you have an inoperative intake flapper system you will be down roughly 50 ft/lbs of torque. Significant enough to notice

If you have say a clogged cat, it can feel like it's holding the car back .

If you have a bad charcoal canister, its suuuuper easy to delete and get zero codes after doing it. And the best part, you'll never have the fuel clicking off early again. I've done this to my car and haven't had it click off one time before it was suppose to. Best mod to date lol

Have you checked fuel trims or done any data logging while this is happening? I think fuel trim data is key here.



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[notasausage]

If you have say a clogged cat, it can feel like it's holding the car back .

This right here. My mechanic has told me the exhaust is overdue for a replacement, specifically the cats. I believe he even said there's some crap rattling around and at some point the car may not run at all until I clear them out or replace them. I've been looking at the FI downpipes and high-flow catback exhaust for a while, but it's a significant investment at $2,500 before labor...

If you have a bad charcoal canister, its suuuuper easy to delete and get zero codes after doing it. And the best part, you'll never have the fuel clicking off early again. I've done this to my car and haven't had it click off one time before it was suppose to. Best mod to date lol

I didn't even know deleting was an option! Any info on difficulty, etc.? I'll do a search and see what's out there.

Have you checked fuel trims or done any data logging while this is happening? I think fuel trim data is key here.

I plan on doing some data logging this week, there's another intermittent issue where the traction control and ABS lights pop on during a hard corner but disappear after a while, or after I shut down the car and start it back up. Need to look into what's going on.

[VinnysS4]

The charcoal canister sits under a round plastic cover at the rear of the car. It is tucked up under where the spare tire sits on the inside of the car. There are three lines going to the charcoal canister, if I'm not mistaken two are a 5/8 inch and one is a 3/8 inch inside diameter hose. You buy a T that has two sides that are 5/8 inch and one 3/8 inch coming off. You need to buy a short section of 5/8 inch hose (a foot should do) to connect it all up. You literally just put the T in line with the hoses, clamp It Off on all connections, and you are done. No codes whatsoever and you can fill it up without issue. The only downfall I have found is when you are filling the tank, sometimes you will smell some fuel. This is normal due to not having a charcoal canister to filter it out. Smell goes away as soon as you leave the gas station

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