High-flow fuel pump install in an A4 (somewhat of a How-to)

[xr4tic]

This mod is not for everyone. If you're not making at least 250hp, I wouldn't even consider it. I'd say 290-300hp is borderline. This will not make your car go faster, unless you are having fueling problems. This is an inexpensive mod to do, especially when compared to rebuilding your motor after running too lean. Think of it as cheap insurance.

This was not a straight drop-in that I was originally lead to believe, but it is doable. It requires a spacer and some special tools (which I didn't have)

This was done in my 1997 Audi A4 quattro. Other A4 model years should be the same, but I can not be 100% sure. Same thing for the S4, I know it has a different pump, so this may or may not work for it.

I got a Walbro 255lph High Pressure pump from Auto Performance Engineering for $113.40
This is the kit for 85-97 Mustang, part number FPF003.
You can buy the same exact pump from Holley and pay an extra $50-$75 for the Holley name printed on the box (part number 12-915)

MAKE SURE you buy the HIGH PRESSURE version. A standard pump can choke because of the fuel pressures a turbocharged motor runs.

For reference, the stock pump flows around 90lph. I think the S4 pump is around 127lph.

BEFORE you start, the tank should be less than 1/4 full of gas. The pump is submerged, and you don't want to be splashing gas around while trying to remove it. I had 1/4 tank, and I still ended up splashing gas into my eye.

You'll also want to do this in a well ventilated area, there will be plenty of gas fumes floating around.

Click on any pic to enlarge it.

First, removing the old pump:
1. Remove the gas tank filler cap to relieve any pressure in the tank, then put it back on.

2. Remove the cover from inside the trunk. This is the round black cover under the carpet, behind the passenger back seat.

3. Disconnect the electrical connector, then remove the crimped-on hose clamps. Label the hoses so you do not get them confused. Put a rag over the hose connections as you pull them off. The supply line may be under pressure, and you don't want gas spraying all over you and your interior.


4. There is a special tool for removing the cap on the tank. According to the Bentley manual, it's part number is 3217.
I used a screwdriver and a small hammer. If you go this route, use a screwdriver with a wide dull blade to prevent it from trying to chop the fins off. It will require quite a few taps to get it free.
Move the screwdriver around to prevent mauling any one particular fin.

5. SLOWLY lift the cover off. There are two electrical connectors that need to be disconnected, and the return line needs to be disconnected. The electrical connectors have some slack in them, but the return line doesn't have much, disconnect it first. Leave the supply line (flex tube) connected.


6. There is a special tool to remove the actual pump from the tank. Part number is 3307 according to the Bentley manual. Again, I did not have this tool, I had to make one.

There are four indents on the fuel pump that the tool engages to unlock the pump (twist to the left slightly)

Note the four notches, also note the V-notch. Remember where this notch is before you remove the pump, as it goes back in the same way.

My homemade tool:

The spacing is approx 3.5", and maybe 6" or 7" long.

7. Pull the gasket off the top of the tank, and wiggle the pump assembly out. You have to be careful to not damage the level sending unit.

The removed pump:



Take a break and wash the gas fumes out of your eyes.


Now the fun part, putting the high-flow pump in.

The old pump pushes right out. I used a 14mm socket under the outlet, set it on the bench, and pused down on the inner housing, and it came right out.

Remove the flex tube and electrical connectors from the old pump. My pump had the connectors labeled + (black wire) and - (brown wire) Make note of this.

Here's the comparison:


The high-flow pump is on the right. this is from memory, but I think the high-flow pump is 1.55" in diameter, the old pump is 1.69" in diameter. The new pump is also 0.7" shorter.
The new pump has the outlet in the center, the old pump is offset.

The bottom of the pump housing will need to be trimmed slightly to allow the new pump to go in.

Ideally, a spacer that is 0.7" in length, 1.69" in diameter, and 0.2" thick would work great. I did not have such a spacer, so I used a piece of 1.75" tubing, cut a small section out of it to reduce the diameter, dimpled a couple of the edges, and put it in.

If you look closely, you can see the spacer I put in there.


You'll want to put the spacer over the flex tube, connect the flex tube to the new pump using the supplied hose clamp, then connect the electrical connector to the existing wiring. On mine, Black is positive, Brown is negative. You can double check this by using an ohmmeter to check the electrical connections in the car.

Once everything is hooked up, drop the pump in and push the spacer in. Use cable-ties (should be gas resistant) to hold the wires to the flex tube.

Now remember when I said to make note of where the V-notch on the pump assembly was in the car?

The filter sock has to go in a specific way to clear the tank. If you shine a flashlight into the tank, you can see roughly how to index it.

The mustang filter sock was slightly too long. I used a pair of wire cutters to snip the plastic frame on the outside, taking care not to cut the filter material, and bent it up. The sock should not extend past the diameter of the pump housing.


With the spacer in, and the filter sock on tight, the pump will not move.


Now the fun part, putting everything back in. Installation is the reverse of removal

When installing the cap, it goes on pretty hard. Make sure it's fully seated, if there is a gap between the cover, and the cap, then it's not on all the way.

Next weekend I get to put in a new fuel filter. I'll cut the old one up to see how much junk is in it after 85k miles.

If there's anyone out there with the ability to machine a proper spacer, I'll be more than willing to test it out

[4kq]

Thanks for the detailed and clear explanations. (although I would advise removing the leads from the battery first, particularly with the sound system in the trunk...)

So much for "identical" pumps!

Does the very high volume/pressure of the pump overwhelm the FPR?

[Audiboy]

same inside housing when it is pulled out as in your picture. It flows 144 lph according to bentley and some calculation compared to the A4 (1.8 and 2.8) pump at 108 lph. That's a lot of fuel. S4 hp junkies can benefit from your work big time too

[PanTTher]

I've heard these pumps are louder in general. What happens when you turn the ignition key to the ACC position? Can you hear the pump run?

[WYSIWYG]

[xr4tic]

I disconnected the stereo power wire first. It is probably a good idea to disconnect the ground wire on the battery as well.

I actually have the amp rack over the fuel pump cover, so I had to move all that stuff out of the way first.

The high volume shouldn't overwhelm the FPR, unless maybe there is a restriction in the return line or something like that.

[xr4tic]

the 108/144 is probably 14V. The 255lph is rated at 12V, so at 14V it's probably closer to 280lph.

[xr4tic]

I can't say I could really hear a difference, of course, I wasn't really paying attention either.

I can't hear it over my exhaust at idle (3" downpipe, no cat, 2.5" Scorpion from DP back)

[xr4tic]

The volume the pump puts out goes down with fuel pressure, so it depends on what base fuel pressure you're running. I figure with the stock 4-bar FPR, running 25psi of boost, it's good for 500hp or so. Still more than enough......

Or is it?

[Audiboy]