B7 Audi A4 2.0T ran out of gas, now intermittently won't start or run well

[dabigtuna]

Hi all,

Last summer, I acquired a 2006 B7 A4 Quattro S-Line w/ 2.0T + 6-speed. The car needs a bunch of work (timing belt, brakes, clutch) so I was only driving it occasionally to keep it fresh while I was looking for a job so that I could pay for parts (got said job earlier this year, yay). Unfortunately, I ran the car out of gas in October or November (can't remember exactly). I ran to the gas station in another car, got like 3 gallons of 91, and poured it in the tank. The car then started right up and drove fine going to the post office and back. Unfortunately, a couple days after that, I went out to the car, and it would crank but not start. I checked the fuel pump fuse, and found it to be good, so that wasn't the culprit.

A few weeks later, I tried starting it again on a whim, and it started right up! I was surprised but took it out for a spin only to find out that, once I hit ~3000 RPM, the engine hit a wall (felt like loss of fuel) and I would have to back off to keep it running. Then, I was moving it into my driveway a month or so later, and stalled it by accident (driveway is a slight hill, I was sloppy) and it wouldn't restart, so I pushed it into my driveway, where it has spent the winter.

Anyway, I've been googling, and haven't got a ton of results other than the usual possible overheating of one of the fuel pumps or air in the lines. A bad fuel pump seemed like a likely culprit, since the car felt like it was cutting out when I asked for more than a certain amount of fuel. I figured that bleeding the line and then checking pressures from the in-tank pump and HPFP would be the next logical steps, but looking at instructions for that, it seems like the main way of checking pressures is through VCDS. Is there any way of manually checking fuel pressure from either pump, such as one might do with the typical Schrader-valve fitting found on most common-rail IDI cars, or is reading the sensor data the only option for that? If it is, I guess I'll bite the bullet and buy the Ross-Tech solution?

Thanks!

~Jooseppi

[IbisB7stage2]

There's a good chance your fuel filter is filthy after running the tank down to the minimum. its an easy swap on these cars thankfully. I don't know of other pressure checking means besides VCDS, but it doesnt seem unreasonable. There is a pressure relief valve (schrader style) on the high-pressure fuel pump.

[dabigtuna]

There's a good chance your fuel filter is filthy after running the tank down to the minimum. its an easy swap on these cars thankfully. I don't know of other pressure checking means besides VCDS, but it doesnt seem unreasonable. There is a pressure relief valve (schrader style) on the high-pressure fuel pump.

Thanks for the reply! That’s an interesting idea on the filter— I’ll look into it. I suppose if I disconnect the filter, I could also check the flow from the low-pressure pump by running it into a gas tank and seeing if the flow is good.

[aluthman]

There's a good chance your fuel filter is filthy after running the tank down to the minimum. its an easy swap on these cars thankfully. I don't know of other pressure checking means besides VCDS, but it doesnt seem unreasonable. There is a pressure relief valve (schrader style) on the high-pressure fuel pump.

While it definitely could be the fuel filter causing the issue, it’s not because it was run out of gas. The fuel pump always sucks from the bottom of the tank regardless of fuel level.

[Theiceman]

Personally I think it's more likely to be a bad pump if anything

I would think more fuel pressure system tests are in order before swapping anything.
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