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Fuel pump testing and replacement on Audi WR, WX, MB, GV ur-quattros

Parts required:

• 431 906 091A Fuel pump - WX, WR, GV, KW
• 893 906 091A Fuel pump - MB
• 893 906 091E Fuel pump - RR
• 431 906 095 x2 Rubber mounting for fuel pump (you will need to replace them)
• 443 133 741A x2 Rubber mounting for fuel accumulator (you will need to replace them)
• N 013 812 8 x2 Crush washers
• N 013 818 2 Check valve sealing washer - optional
• N 900 961 01 Clip
• 8 to 10 stainless 6mm nuts - this is one of the few places on the car where using stainless fasteners makes sense.

Testing procedure (WR and MB engines):

• Ensure adequate ventilation and check no sources of ignition - review safety
• Put 900ml of water into an empty 2-litre plastic soft drinks bottle - labels removed
• Mark the level on the side of the bottle
• Empty and dry the bottle
• Remove the fuel pump relay (Relay 10)
• Fit a lead with a spark-free (sealed) switch between the large contact in the fuel pump relay socket parallel to the side of the fusebox and the large contact at right angles to it. Check that pressing the switch runs the fuel pump. Maximum current is 8.5 amps
• Disconnect the fuel return line at the metering head
• Fit a length of hose from the fuel line leading into the bottle
• Run the fuel pump for 30 seconds or until the 900ml line is reached
• Carefully return the fuel to the tank - it is illegal to store fuel in plastic bottles
• If the 900ml line is not reached in 30 seconds, replace the filter and retest

Replacement procedure:

• Before starting - check that the fuel pump has not been jumpered. On all ur-quattros, the fuel pump is explicitly controlled by the ECU which will cut the current supply if the engine over-revs or overboosts to prevent engine damage. On some cars, this has been bypassed and the fuel pump jumpered directly from the ignition so a stronger wastegate spring can be used. Apart from the danger of engine damage, there is the safety issue of the pump running after a serious frontal impact stops the engine, and also of damage to the pump if the fuel tank runs dry. The fuel pump should not run with the ignition on and the engine not rotating.
• Disconnect the battery
• Apply a clamp to the thick hose from the tank so as to seal it completely. If the clamp available does not completely block off the flow (lever types tend not to) the "contraceptive" protecting the inlet of the new pump during transit will adequately block the end of the hose.
• Disconnect the hose from the pump.
  BEFORE PROCEEDING CHECK THAT THE OLD HOSE FITS THE NEW PUMP.
  If not - refit, unclamp, and start finding the right size of hose for the new pump. If you have to change the hose, the process includes completely draining the tank
• Disconnect the main fuel line that goes forward from the fuel accumulator to the filter. A 14mm flare nut spanner with a locating skirt (e.g. FACOM 43) is extremely useful.
• Disconnect the power connections
• Undo the bolts and screws holding the fuel pump and accumulator to the bottom of the car, and remove the whole assembly to a bench
• The outlet from the fuel pump is in two parts:
  • a check valve screwed into the pump
  • a banjo fitting bolted into the end of the check valve.
• All attempts to unbolt the banjo fitting ALWAYS result in the check valve coming away from the pump instead - unfortunately, this leaves you with a dilemma. You can just destroy the electrical terminals and wind out the check valve, then remove the banjo from the check valve on the bench. Or, you can try and grip the check valve sufficiently tightly to remove the banjo bolt. This takes skill, determination and equipment - SC12 ViseGrips, specially ground down 17mm open-ended wrenches or water-pump pliers with the back jaws ground out.
• Beware that the pump to filter to reservoir pipes have only limited flexibility - the pressed-on pipe that fouls the terminal posts and is the reason you can't just wind out the check valve is AMAZINGLY delicate. If you're going to use any force, wrap tape around it to protect it from the terminal posts.

While you're struggling with the check valve banjo bolt on the bench, just remember you could have been trying this trick upside down under a car with fuel dripping into your nose, rust dropping into your eyes, and the pump mounting plate in the way. This process loses all of its attraction if you then discover the old hose doesn't fit the new pump.

At least you can have a cold beer on a bench. Some prefer ice-cold Scrumpy Jack in a Thermos-insulated mug - Nature's antidote to the taste of fuel

Do not, under any circumstances, grip the new pump in a vice.

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Contact Phil Payne by email or use mobile/SMS 07833 654800