Jack88

Well, I don't know what I did to anger the gods at Ingolstadt, but no sooner than I get my suspension back up and running properly, I get a check engine light for banks 1 and 2 running lean. The car seems to run and drive without issue at the moment, the only possible symptom I noticed before the light was sometimes on startup it would rev to 2200-2400 rpm for a few seconds before settling down to normal and today on a warm start it hit idle speed for a moment, dipped to 500 rpm momentarily and returned to normal rpm. All of this is in park still, by the way. My suspicion is the fuel pump that only operates during startup is failing, and that seems to be the suggestion that usually accompanies these posts. I can't remember which pump is the one for start up off the top of my head. Really, I'm just fishing for alternative explanations before I just order an OEM pump at $346. Man, I don't think anyone else on this forum has bought a running and driving car that has had so many things to address that didn't come about from negligence or abuse in such a short time. I have had the car since March and not even put 2000 miles on it!

MP4.2+6.0

Need more data, but don't order any "fuel pumps" yet. There is no fuel pump that only runs during warm up, whether a port injection like yours or the later FSI's. On a port, there or two pumps, both in tank. One is primary pump, and other is basically a transfer pump from side to side as I recall. What runs during a cold start warm up for a minute or two is the air pump that is part of the secondary air injection (SAI). In American car speak, what many used to call the smog pump. That pump pushes air via the combi (combination, along with EGR function)) valves into the exhaust, while at the same time the ECU richens the mixture which lights off (burns) in the exhaust area to heat the converters faster. I would expect you would have codes for SAI issues more directly. You can also check the function of the SAI pump, for example by applying power directly to it, or using VCDS to spin it up in test mode. They do burn out sometimes. Car has two combi valves BTW--one on each head--which is why with a both banks (heads on a V8) lean code I am pointing more at a full engine systemic issue like the air pump or a pre intake manifold air leak.

Most common area for lean codes on both banks would be an air leak on the intake side before you get to the intake manifold itself. If it is both banks, look particularly at anything between the MAF and the intake manifold----those last couple of clamp connectors, throttle area, any hose take offs there and the like. After poking for an air leak; confirming air pump is working and its hoses connected, free and not compromised; and watching for any SAI codes, then perhaps suspect the MAF. You can check its flow rate readings by instrumenting it with VCDS and going for a drive. Its peak flow rate in grams per second should be 80% or more of rated HP as a rule of thumb. Rounded off (you can do the calc), that means at least 250 g/s flow. Peak flow that is easy to read is typically near redline out of 1st or 2nd. Either record the test run via VCDS, or have a ride along partner to watch the data while pushing last thousand or so RPM in probably second. On an older ride, worth knowing an MAF is still up to snuff for smooth operation and power.

And yes, it could ultimately be a fuel pump. The transfer one can show up when car gets flaky yet gauge says it has gas. Posts that I recall casually on it are more like car dies completely, but indirectly I think the transfer pump is not moving fuel across the hump of the tank to the other side, so main pump runs dry. Main one can also just get weak or crap out completely. But that's just very casual description; there are better ones in the D3 and 4.2 port related SSP's about how the fuel pumps work. The FSI ones have another set of high pressure pumps, but not relevant pre 2007 for 4.2s (or any D3 W12).

Jack88

Ah, according to the diagrams I'm seeing, there are 4 pumps in total. A transfer pump and regular pump on both sides of the tank. I had thought that one pump was used only during startup but I wasn't sure. I'll look into it and the things you have suggested.

MP4.2+6.0

I think you will find there are two actual pumps--things with motors, or more generally moving parts. The other things referred to as a pump probably are Audi's terminology for suction/vacuum creating devices (like vortex shapes and/or orifices) and related lines, like here to pick up fuel. Always confusing to me when they call something a pump, yet it doesn''t have moving parts. The FSI motors have four actual pumps--same two in the tank and then one high pressure one (HPFP) on each cylinder head. D4 simplified it to one tank pump that can pull fuel over the saddle/hump without needing two in there.

dvs_dave

Jack88

Okay, so what I think I will do is change the fuel filter and see what happens. I don't think it has been for about 50k miles at least, maybe original, hard to say. Perhaps if that doesn't do it, I'll just have to wait until more obvious symptoms show up to make a diagnosis.

dvs_dave

ScottCNelson

The notorious G410. It's notorious and cheap and easy to replace.

P310B/012555 - Ross-Tech Wiki

dvs_dave