UncleSam

I now have two of these cars, a 95 and a 96. There is a couple of problems that's probably common for these cars, as they appear on both. I have a broken pin in abs module connector on both (same pin too!), the drainage clogs, and what I wanted to discuss: engine doesn't get fuel when you have about half or 1/3 of the tank left. This is some type of failure in the system of hoses that are supposed to bring fuel from the left tank to the pump in the right tank. So I'm wondering if anyone has fixed this, what the actual problem is, and if it's possible to fix without new parts or what parts are needed. Thanks in advance.

BrianC72gt

If you are not getting fuel at about 1/3 tank, either

1. your original pump is dying,
2. the wrong pump was previously installed and it doesn't have the extra port on the bottom,
3. the correct pump was installed, but the pump assembly did not mate correctly with the assembly in the tank,
4. one or more of the hoses on the bottom of the tank have come loose from the cup assembly or there is a bad hose inside the tank .

or maybe a fuel filter or FP relay, but those don't jive with your symptoms.

jfrahm

Good advise. Also there is an aftermarket fuel pump that "almost" works, it has the port on the bottom but does not flow enough to run the scavenge system. I sure had fun with that.
The system actually has the pump more-or-less in the middle and two scavenge pumps in the tank "feet" which are powered by fuel at high pressure. They return more fuel (at low pressure) than was sent down.

UncleSam

Thanks for answers. I'm thinking it's number 3 or 4 of Brian's list there. I doubt the pump has ever been changed. What's the chance of the tube system loosening from the pump "by itself" or maybe running over something that hits the tank in the right place? I'm going to take a look to see if it's loose, this on a parts car where I have emptied and lowered the tank. Hopefully it will help me fix the same problem on the one I'm going to use.

BrianC72gt

Zero percent chance. Round about a hundred thousand miles, the pump dies. It is a single gas tank, shaped like a saddlebag, and a single powered pump. Don't overthink it. This routine wear item has been analyzed to death, and can be clearly understood by using the special tool called the "search" button.

Swap the pump with a proper VDO and move on.

UncleSam

Care to explain how the pump is at fault when it delivers fuel perfectly until there is about half a tank left? It probably empties the right part where the pump is seated, and draws nothing from the left part. Seems pretty obvious to me that the system of pipes supposed to draw fuel from the left part is at fault, not the pump itself.

BrianC72gt

Sure thing. The pump delivers fuel in a very conventional way until the tank is about 1/3 full. The pump suction port is submerged and it sucks in fuel and pumps it through the lines. Simple.

Below 1/3 tank, the pump is no longer submerged. It relies on these far reaching tentacles at the bottom of the tank to lift fuel into the cup in which the fuel pump sits and then it pumps it up like normal. That's why this pump has an extra port that no other fuel pump has.

Above 1/3 all the pump has to do is draw fuel from the bottom of the pump (very easy). Below 1/3 tank it has to do two (2) things: 1) suck fuel up from below to fill the cup in which the pump sits (harder to do), and; 2) pump the fuel in the no longer submerged cup (easy to do).

When the pump starts to go out, it fails at siphoning fuel through the tentacle pipes to fill the cup. The pump IS NOT SEATED ON THE BOTTOM OF THE TANK It DOES NOT suck out all the fuel on the right side and not the left side. Absolutely Wrong. It sits in a cup. Once the fuel level falls below the brim of the cup, it relies on the siphon pipes (like plastic accordion straws) on the bottom of the cup assembly to pull fuel up into the cup. The only way the suction hoses break free is if someone wrestled with a previous install, and tried to pull the assembly out without first backing the bolt out half an inch or so, lifting lightly on the pump assembly and knocking the bolt head down to separate the cup from the male spigot and then removing the bolt completely before lifting the assembly out. If you don't drive the cup assembly down with the partially removed bolt, then you are pulling against the plastic tentacle connections when you yank the pump assembly from the tank.

I've replace several pumps and came up with a method to cut out the FP assembly with a foot long hole saw I welded up when the captive nut in the cup assembly broke loose. This required siphoning out all the fuel, filling the tank with 22 gallons of water, drilling out the assembly without damaging the parts inside the tank, sucking out said 22 gallons of water with a shop vac, magnet the metal shards, vacuum the plastic shreds, then long arms to dry the inside of the tank from both sides, completely pull out ALL of the tank's guts, replace and epoxy the captive nut and reassemble. 12 years ago still going strong on the replacement pump, zero issues.

I also came up with a sure fire way to know with absolute certainty that you've installed the pump correctly because Audi's method is ****ing idiotic: Drive around with a gas can in the tunk in case it dies suddenly and unexpectedly...like on the highway or making a left across traffic. WTF?? Install the pump, then remove the relay cover in the passenger's footwell under the carpet (4 screws - mdf cover), remove one screw and slide out the FP relay, gebntly remove the FP relay cover, push FP points closed with a folded matchbook cover or something equally gentle. Remove Banjo bolt on the output sideof FP assembly in the trunk, swap it with a threaded hose barb and six feet of cheap-*** clear plastic fuel rated hose. Switch the key to RUN and pump the tank Dry. Switch off. Add two gallons of fuel. Switch back on and pump out at least 1.5 to 1.75 gallons. If so, you are good to go. If not, suction spigot misalignment.

So, Yes, I humbly suggest you take my word for it.

BTW don't go for the exotic problem. These pumps ALL wear out. Hours of operation would be a better indicator, but in miles, they all died from as few as 80K to as high as 130k miles, but they all die.

jfrahm

In the pic below the fuel pump lives in the cup (about #18) which sits up pretty high from the two tank "feet".




The most likely issue you have is that someone put in a generic fuel pump that lacks the little extra port on the bottom to drive the scavenge system. 2nd most likely is that they did not get the assembly back together correctly and the pump is not sending fuel down to the scavenge system.

-Joel.

audijim113

Brian, where are you located? My wife's 11998 D2 is living on borrowed time and I would expect the pump is reaching end of life. I have a pump which I kept after it was replaced (by a shop) from a previous 2000 D2.

I cleaned and replaced the internal motor on that pump, wrapped the entire unit in plastic and put it on the shelf. None of the local shops near me will do the job, using my pump and want to sell me new. I'm too old, too fat, etc to get in the trunk and do it myself. Looking for some smart dude who knows what he's doing.

If a "smart dude" was anywhere near Michigan and wanted to attend "Eurohanger". (very large Eruopean car show event) which is a couple miles from my house. Being a tourist town, motels are not cheap. I have room and would provide lodging if a "smart dude" were interested

BrianC72gt

A "low moron" has 2 daughters, a cat, dog and a girlfriend. He's also a little fat and just past 50. I would give my left nut to go to Eurohanger. But alas, I'm in NorCal, heading to NYC to see family this Summer.

I'm sure you can find an Indy nearby. This job is not nearly as bad as everyone makes it sound. I give it 3 out of 5 wrenches on the difficulty scale. It might even be a two.

The only trick you need to know is to start inserting the complete unit 90ish degrees counter clockwise to the alignment mark and kind of turn it in clockwise like a screw, holding it up slightly as it pulls itself down. Once the alignment marks are lined up, then you push it straight down to drive the suction port home into the corresponding receiver in the cup. The mistake people make is to let the unit fall down and just turn it, then the male suction probe is too low and ends up next to - not in - the female receiver.