abcxyzzz

I have a 2004 A4 3.0L Quattro Wagon.

I was driving this morning, and after 1 miles of leaving from my house, the car started sputtering while I was driving and the yellow check engine light started blinking. I pulled into the turning lane to get off the main road, and as I turned and pressed the accelerator, the car would barely move, it was sputtering with almost no power.

I got it to the side of the road and had it towed to my house. When I turn on the car it idles really low and fluctuates between 450-600 rpms and sputters and shakes.

Any idea what the problem could be? Tow truck guy said it might be fuel pump or spark plugs, or maybe the OBDII sensor?

Please help...thanks.

abcxyzzz

Car has 117000 miles on it.

I checked the service records (I bought it used a year ago and have all the service records) and the OBD sensor doesn't look like it's ever been replaced. Don't those usually go out after 100k miles? Would that cause all the loss of power?

abcxyzzz

So my friend and an OBD II scanner and here's what it said

P0300 Random / Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 2 Misfire Detected

More info on the problem, I had 1/8 of a tank of gas left, and my fuel filter has been humming for 8 months when the fuel is below 1/4 (I even changed a new fuel filter 3 months ago, so it's probably the fuel pump that's humming).

After car was towed home, it sat for 4 or 5 hours before my friend came over with his OBD II scanner, it started fine this time but showed the codes above. My friend though there might be some debris kicking up in the fuel tank since it was low and suggested I fill it up and see what happens. We went to fill it up and then re-ran the codes. NO ERROR Codes. Is that weird?

He suggested I changed the spark plugs & spark wires. The last time the plugs were done were at 75000 miles (car has 117k miles now), don't think the wires have been changed.

Any insight from anyone based on the above? Thanks!

lyleswk

If your pump is in fact noisy, it is probably just on the edge of not providing adequate fuel pressure. Just as a note, when you fill up the tank, the pressure from the weight of the fuel may be enough to up the head pressure so you have no issue. Once the tank gets low, that head pressure is much lower and your pump is marginal. Doubt it is your plugs / coil packs as the problem is solved with a full tank of fuel.

abcxyzzz

Your logic certainly makes sense regarding the coils vs fuel pump. Is there a way to know for sure it's the fuel pump that's causing the problem, other than replacing it (which I think it's quite costly) and running the tank down to low to see if the problem comes back? I don't want to replace it and then find out the problem comes back and it wasn't in fact the fuel pump causing the loss of power...

I called up one place told him the symptoms and he kept telling me to come in and boasting that they are one of a few shops that have "utilizes the most current and up-to-date factory VAS PC Scan tool and software." - that's not going to tell the problem though is it? I don't think that tool makes him more qualified to diagnose the problem than someone that didn't have it does it?

lyleswk

Test the fuel pressure just before going into the injectors. I have not done this on my Audi and would have to look at the fuel system routing to determine where (or maybe some others have done this), but on my 27 year old 300ZX turbo, I have tested the pressure just past the fuel filter which is installed inline just before the injectors vice under the car near the fuel pump on the the Audi. I would do this with fairly low fuel. And no, the VAGCOM does not have a fault code for low fuel pressure to my knowledge. I would show up in misfires, lean run condition, etc.

Oh, and I have the latest VAGCOM PC tool, so I guess that ranks me with your indie

a44me2

Perhaps your fuel guage is inaccurate and you were nearly out of fuel. Were you on a hill or slight incline at the time of the problem?

abcxyzzz

I was not on a hill at all.

I don't think it's the fuel guage that's inaccurate for two reasons. 1) after the car sat for 4 or 5 hours, it started and idled fine (before it wasn't idling fine), just the check engine light was on. 2. When i filled up the gas, it only went to about 13 gallons, so 1/8 tank would still have 2 gallons or so which added to the 13 gallons i filled would make 15-16 gallons (the capacity of the tank).

Lyleswk,
I'm leaning toward your earlier response regarding the fuel pump possibly being the culprit as the car has been running fine this week with a sufficient tank of gas. I don't exactly know how a fuel pump works, so you're saying that when the tank is almost empty, there's not as much pressure (weight) on the fuel pump to make it work properly? Will this only happen with the fuel tank is low, or is it going to die unexpectedly one day and leave me (my wife actually, since it's her car) stranded?

You have one of those VASCOM PC tools? Why did he make it sound like it was so special? on his website he says he is like 1 of 16 shops in California that have it, like it was such a rarity...

Gingerbread man

Could it be the fuel filter is full of junk? I know people report fuel pump acting up when the filter is dirty. When was the last time the filter was changed? Manual says it should be done every 60K. It's not hard to change BTW (just did mine).

abcxyzzz

I don't think it's the fuel filter, I had it changed 6 months ago when I first noticed the humming noise coming from the pump & filter area when the gas tank was below 1/8 of a tank. Some people recommended to changed the fuel filter, so that's what I did, but the humming is still there, so more than likely it's the fuel pump causing the humming.

In terms of the loss in power problem now, so far Lyleswk's theory seems the most logical it being the fuel pump. If it was the fuel filter being clogged with junk, would it still be doing it whether the gas tank was full or low? Seems the problem has gone away for now with sufficient gas in the gas tank...