QUA8RO

All,

In guiding my aging A8 through the November of her life, this weekend I engaged in a fuel-filter change but am at a loss for getting fuel through to the engine to start her back up.

I'm seeking wisdom or experience. I thought this should be a piece of cake.

Here's where I'm at:

The fuel pump is operational. When I put the key into the ignition "prime" step, the pump runs for its second and I get gas coming out the filter's supplying line. I've hooked that up to the filter, primed a few more times and I get fuel coming out the outlet of the filter. I've hooked up that line and moved to its other end, at the fuel rails on the engine (I'm pretty sure that's the other end of this line...) and cannot get fuel to come out its other end, despite priming with the ignition-switch tens of times. There is no air pressure or fuel coming out at the fuel-rail end when I prime the ignition. I can suck gas from this end. Not tasty, but it won't be the last time in my life I get gas in my mouth.

When I ignition-prime, I do hear a gurgle in the fuel filter, which I assume to be air in the filter.

Is there a bleeding process or priming wisdom I'm missing?

I'm contemplating wiring the fuel pump directly so I can get it to run more than the ignition switch's one second prime, but am a bit leery of that. Seem's like I'd be risking a his-last-words-were-try-that-again moment.

I'm in no rush and have other transportation, but am truly surprised this has been difficult to get moving.

S8ilver

I changed my filter not too long ago. There is no bleeding process that I'm aware of; it just fired right up afterwards like normal.

Did you reinstall with 4 new washers? I wonder if you have a leak.

QUA8RO

Thanks for the reply.

Yes, I was pleasantly surprised that my replacement filter came with the brass crush-washers; those were used and I don't have leaks in or out of the filter.

From reading the thread below, it looks like direct-wiring my fuel pump will let me flush the system. I'll try that this evening to see if I can get fuel to the high-pressure side of the fuel rails at the engine. If so, I can't imagine why it wouldn't start. It's *always* started in my twelve years of ownership.

https://www.audiworld.com/forums/a8-...think-2846529/

If it doesn't, I may be on to crank position sensors and fuel pump relays. This takes my back to my 83 GTI...

QUA8RO

Well, now I'm flummoxed.

I direct wired the fuel pump. Whir, whir; gurgle gurgle, sounds of gasoline moving through pipes. Nothing coming out at the high-pressure side near the engine's fuel rails.

All I can think is:
1) Blocked fuel line
2) Looking at wrong fuel line at the engine end. It should be the high pressure feed into the rails, right?
3) Fuel pump not pumping. But it whirls and gurgles.

S8ilver

Stupid question, but you installed the filter in the proper direction of flow, right?? Arrow pointing toward front of car??

QUA8RO

Not a stupid question at all. But yes, it's in there correctly. Actually, due to different size of connecting bolts on the in and out lines, you can't put it in backward.

Today's approach will be to:
1) unhook the "out" line and again verify I can pump through filter
2) see if I can blow out from the high pressure feed line back to the filter

BrianC72gt

Why did you change your filter? Was fuel system acting up?

QUA8RO

Yes.

I've been through a lot with this car recently. I've had her for twelve years, and since December did the oil-cooler pipe replacement (what fun!), an ignition control module, rear springs, and even fixed the windshield squirters. At 245k miles, she's given me more than my money's worth, but now it's kind of like having a project car to keep going, like you see on all the motor-channel shows. It's a bit of a hobby and I enjoy throwing a couple hundred at my "thousand dollar car" every now and then.

Since I replaced the ignition control module in January, I've had this occasional, random engine stumble. Every 8-10 seconds, hiccup, and fine. Absolutely drivable, so I've simply been waiting for it to more clearly show itself. Worst case, she dies. It occurred to me last week that it might be the fuel pump, and I tried to recall the symptoms when my fuel pump died about two years ago. And then I thought, "well, the fuel filter has never been changed on my watch," so for $20 why not see if it's the simple thing.

Which led to this thread.

Which, as of this morning, has led to a new replacement pump and gasket set on order. I was able to easily blow out the fuel line last night, but was unable to get any fuel out of the fuel-pump at the filter end. I was able to get some out on Monday, but I think it's simple not got enough pumping power. It's giving up. A new one won't hurt it. It'll be a fun project. I've got a B6 S4 to get me around in the mean time.

It's foolish to throw a thousand dollars at a thousand dollar car when all you'll have when you're done is a thousand dollar car, but, well, she's an A8 and her tires are still good. And this is good experience for both me and the kids to diagnose and fix things.

BrianC72gt

You can also remove the passenger front carpet....three screws on the relay box cover, slide out the relay tray with the fuel pump combination relay...carefully pop the cover off of it, use a matchbook cover or the like to hold the FP relay contacts closed, then toggle the fuel pump on and off using the ignition switch...to RUN position...no need to crank it. A handy way to bypass the G20 sensor, and to pump out the tank to nearly empty when you reinstall a pump.

Your replacement pump is 2 years old? Did you ever run it down to nearly empty since you replaced it? If it doesn't align properly with the internal cup/siphon system, the pump will stop pumping just below a half tank. If you pour in a pint of gas, it primes the cup directly regardless of the level in the tank...so it would start...sputter..then die if your pump is misaligned.

Have you got VAG com? any codes?

Good luck,

Brian C.

QUA8RO

I'm aware of the ignition switch run position vs cranking the engine. I've simply bypassed all of this by direct-wiring the pump from the battery, which the German engineers conveniently placed in the trunk with the pump for me. Thanks, fellas!

I tossed a new fuel pump relay in with my pump and gasket kit order. Why not? Let's call it insurance.

Since the replacement pump 2 years ago, I've definitely been able to run the car below half a tank. My typical behavior is to run to about a quarter tank with the occasional foray into an indicated 20mi left (in other words, really low), then fill her up.

She has about half a tank in her now. It occurred to me that by jacking the pump/filter side of the car up, some of the fuel may have trickled over to the other side of the tank, leaving the pump side lacking... I lowered it and then jacked up the other side to pour it back. No dice.

If I read between the lines about priming, should I be able to pour a pint or so in at the gas cap and then test the pump for pushing it out again? I like it! That's easy enough and I will try later today.

I have the VAG "lite" version, but don't see (yet) a call for wheeling that out.* We're talking about triggering a pump motor to push gas through a tube.




*By VAG Lite, I mean that I downloaded the limited version and bought a serial-connector cable over ten years ago. I have held on to the aging old desktop (running win95!!) that the software is installed on, as it's the only one I have with a serial port (for the mouse, originally). Once every couple of years, my airbag light comes on and I need to clear it for the state inspection. It's to the point where I've written the password on the case of the computer with a Sharpie. Airbag light comes on, I wheel it out, hook it up, read and clear the codes, then put it away for another few years.

I'm cheap that way.