|Tech Article Title
|Walbro - V8/A100 fuel pump in C5
The purpose of this project was to upgrade the fuel pump in a 2003 A6 2.7T. I decided to go with a Walbro pump, however, I didn't like the look of the kinky filter sock that comes with it. After viewing some of the documentation on integrating Bosch pumps in the Audi V8/A100 basket (and after getting feedback from VR_Life and HalShizzle), I decided to try this route. The task was to build some sort of housing to fit the Walbro pump into the larger basket assembly. I originally planned to build the housing out of ABS plastic, but thanks to RJV, I realized I was working with bad chemical compatibility info. Anyhow, here's the new route, using aluminum, just in case it might be useful for anyone down the road.
2 x Newcastle Nut Brown Ale
Audi V8 fuel pump basket: 895 201 779 H
Audi V8 fuel pump strainer: 895 201 531 A
Walbro 255LPH HP fuel pump: GSS340
Gas-safe 10mm foam sleeve for walbro pump: 122-3278
2" OD schedule 40 aluminum pipe, 4.5" long
The Audi parts were purchased directly from the dealer, the Walbro pump can be purchased from auto performance engineering, and the foam sleeves are available from import evolution. I purchased the aluminum pipe from a local metal supplier called M&K metal. If you can't scrounge some up near you, they sell small pieces for about 8 bucks or so.
The Audi V8/A100 fuel pump basket and strainer:
The fuel pump strainer and basket and fit together to form a single piece. The bottom of the basket has 3 nubs that correspond to 3 snap-in points on the strainer. The strainer slides over the nubs, and snaps tight in a clockwise motion. At the base of the strainer, there are 3 elevated ridges. My assumption was that these ridges are intended to lift the OE pump off the base of the strainer to allow for less obstructed flow of fuel.
Note nubs (attachment points for strainer) in red circles
Strainer (note snap-in points encircled):
Pump basket and strainer snapped together:
The Walbro GSS340 fuel pump:
The walbro fuel pump (model GSS340) is smaller than the stock pump, and significantly smaller than the pump intended to go with the Audi V8/A100 basket and strainer. The pump sits low in the basket cylinder (which is fine, since space is at a premium in the tank) and is about 20mm smaller in diameter. The task is to effectively increase the diameter of the pump to fit snugly within the basket cylinder.
Pump seated in basket cylinder:
Walbro pump in basket cylinder - offset diameter 20mm:
Putting the pump housing together:
The diameter of the basket cylinder is at about 60mm, whereas the pump itself has a diameter of 40mm. The task was to build a housing for the pump, to effectively increase its diameter to ensure a snug fit in the basket cylinder. For the housing, I used a 4.5" piece of 2" schedule 40 aluminum pipe in conjunction with a thick, foam Walbro pump sleeve. The pump would slide into the sleeve, the sleeve would slide into the (slightly modified) pipe, and the pipe would slide into the (slightly modified) basket. As far as tools were concerned, I used a millimeter ruler, a Dremel with cutting and sanding bits, a vise to secure the pipe while Dremeling it, and a sharpie.
Walbro pump sleeve, 122-3278:
The 2" aluminum pipe fits perfectly into the strainer and rests nicely on the 3 ridges at the bottom. However, I wanted to ensure the best flow of fuel possible, so I decided to cut the pipe a bit to give more exposure to the intake on the fuel pump. I did this by cutting out sections of the pipe to give it "legs" that would rest on the ridges, while leaving openings for greater fuel flow.
Using the sharpie, I marked off the sections of the pipe I wanted to cut out, being careful to leave legs that would rest squarely on the ridges. I decided to make my cutouts 3/8ths of an inch deep, and marked the pipe accordingly. That depth would allow for the pump body to remain fully enclosed while exposing the intake nipple as completely as possible.
Areas to cut out marked in red:
Marked depth for cut at 3/8ths inches:
I used the Dremel to saw out the cutouts:
If you're anything like me, the next step will be to wail on that pipe so hard with the Dremel that you burn the motor out. Send the Dremel into the service center, wait 5 days, and get it back to finish the job.
Once the Dremel came back, I finished the cutouts:
After getting the pipe cut, it was time to stuff the pump and foam into it. It's a REALLY tight fit. I honestly didn't think it would fit in there. The trick was to insert the pump only partially into the sleeve (i.e. pull the sleeve down only about a quarter of the pump's length), and then to insert the sleeve into the pipe from the bottom. With a lot of twisting and pushing, the pump slides into the foam as the foam itself slides into the housing.
Once the pump is fully installed, the base of the pump body should be flush with the bottom of the foam sleeve, the bottom of the foam sleeve should be flush with the bottom of the cutouts, and the bottom of the intake nipple should be flush with the bottom of the pipe's legs. This gives the pump intake about 3mm of clearance from the bottom of the strainer.
Pushing the pump into the foam into the pipe simultaneously:
The base of the pump and foam flush with the bottom of the cutouts:
The base of the intake nipple flush with the bottom of the pipe's legs:
View from the top with pump and foam installed:
The next step was to insert the pipe into the basket, however, the pipe couldn't fit the basket as-is. Instead, I had to LIGHTLY sand two ridges in the basket that were preventing the pipe from sliding in. One ridge is toward the bottom of the opening in the basket, the other closer to the top. You can see the location of the ridges in the photo below - the rough areas correspond to the ridges after I sanded them down lightly with the Dremel.
Sanded-off ridges in basket cylinder:
Once the ridges had been sanded down sufficiently, it was time to insert the pipe / pump housing into the basket cylinder. Again, this was a TIGHT fit. VERY VERY tight. Care was taken to make sure the legs of the pipe would be aligned with the ridges at the base of the strainer when the latter was attached to the basket. Basically, I lined the legs up with the nubs on the basket, to which the strainer snaps on. The ridges in the strainer line up just to the right of these nubs when the strainer is snapped in place.
Once the pipe was lined up, I just pushed that bastard into the basket cylinder, stopping when 42mm of the pipe was left exposed from the bottom. This was the distance required to ensure that the legs of the pipe rested on the ridges in the strainer. 42mm of pipe extended from the base of the basket, and there was 6mm of space between the top edge of the pipe (inside the cylinder) and the top of the cylinder itself.
Pipe pushed in to basket cylinder (42mm left exposed):
6mm offset between top of pipe and top of basket cylinder:
Once the pipe was installed, I snapped the strainer onto the basket and ensured that the pipe's legs made contact with the strainer's ridges, and that the intake had nice clearance. All said and done, the pump / basket looked like this:
All in all, I think that it came out pretty okay. The total weight of the basket with pump / housing is a tad less in hand than a Bosch 044 fuel pump alone. The aluminum should hold up extremely well, and the fit is so darn snug that the pump and pipe are not going to be going anywhere (it really was hard as hell getting them in there, and you don't want to make any mistakes lining things up. If you have to pull that pipe out of the basket, best of luck to you! I made this mistake, and had to disassemble the entire basket assembly to get the pipe out).
Anyhow, I hope this might be useful to someone down the line. If anyone reading this has any suggestions or comments (i.e. if anyone sees something that is just plain stupid or wrong), please let me know!