Quick fuel pump function test - for those that might be needing one.
10-27-2005, 07:16 AM
#1
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Thread Starter
Quick fuel pump function and fuel pressure regulator tests
If you have starting problems and don't know whether its the cam position sensor or the fuel pump, you can at least confirm that it is or isn't the fuel pump. Sean D. (quattro20v) and I used this technique to test our fuel pumps for delivery rates before we developed the fuel pump relay procedure in July/Aug 2004.
To test the fuel pump, you need a long length of wire with a spade connector at one end, an aligator clip on the other end and switch somewhere in the middle - but closer to the spade connector end. Once you have that, you need to open up (break) the inlet connection to the fuel rail (hard piping and braided hose on the driver's side (left hand drive cars)). There may be some residual pressure so only do this when the engine is cold (not a problem if you can't get it started). You need to get a four foot long hose over the connection from the fuel pump. Sean had kept a connector from an old fuel filter so we attached that to the fuel line and then put a hose on that fitting. Either way, you need to get a hose on the connection and be able to run the hose OUTSIDE OF THE CAR to, say, by the front wheel. Place the hose in a gas-compatible container. A 2 L measure cup or graduated cylinder works well.
With the test fuel line in place, pull the fuel pump fuse, No. 17, from the left hand side dash end fuse panel. Stick the spade end of the wire in the right hand side (rear-most) female fuse connector. With the switch in the off position, connect the aligator clip end of the wire to the + post on the right hand cowl side of the engine compartment. With the hose firmly in place in the measuring receptical, turn the switch on for 15 seconds. Then turn it off. At 12v, the fuel pump should have delivered about 675 mL of fuel in that time (Reference - Pg C20-18 in the Bentley) (and the diagram below) If you got less, or none, either your fuel pump is bunned and you need to replace the pump or there is some kind of blockage in the line (i.e. a kink in the hard fuel pump that shouldn't be there).
On a related note, you might want to test your fuel pressure regulator at the same time (you will need a fuel pressure gauge and adapter to do this)Courtesy of kinderutz:
"Test with engine off.
Install remote/jumper cable in Fuse 17 terminal -2- and positive (+) remote connection in engine compartment.
Disconnect vacuum hose from fuel pressure regulator.
Must be: 4.0-4.2 bar (58-61 psi) with fuel pump running
Must be: 3.4-3.7 bar (49-54 psi) immediately after fuel pump (remote control) is switched OFF.
Note:
If fuel escapes during the following pressure check of vacuum connection at the fuel pressure regulator, replace the regulator."
Hope this helps somebody.
Dave F
To test the fuel pump, you need a long length of wire with a spade connector at one end, an aligator clip on the other end and switch somewhere in the middle - but closer to the spade connector end. Once you have that, you need to open up (break) the inlet connection to the fuel rail (hard piping and braided hose on the driver's side (left hand drive cars)). There may be some residual pressure so only do this when the engine is cold (not a problem if you can't get it started). You need to get a four foot long hose over the connection from the fuel pump. Sean had kept a connector from an old fuel filter so we attached that to the fuel line and then put a hose on that fitting. Either way, you need to get a hose on the connection and be able to run the hose OUTSIDE OF THE CAR to, say, by the front wheel. Place the hose in a gas-compatible container. A 2 L measure cup or graduated cylinder works well.
With the test fuel line in place, pull the fuel pump fuse, No. 17, from the left hand side dash end fuse panel. Stick the spade end of the wire in the right hand side (rear-most) female fuse connector. With the switch in the off position, connect the aligator clip end of the wire to the + post on the right hand cowl side of the engine compartment. With the hose firmly in place in the measuring receptical, turn the switch on for 15 seconds. Then turn it off. At 12v, the fuel pump should have delivered about 675 mL of fuel in that time (Reference - Pg C20-18 in the Bentley) (and the diagram below) If you got less, or none, either your fuel pump is bunned and you need to replace the pump or there is some kind of blockage in the line (i.e. a kink in the hard fuel pump that shouldn't be there).
On a related note, you might want to test your fuel pressure regulator at the same time (you will need a fuel pressure gauge and adapter to do this)Courtesy of kinderutz:
"Test with engine off.
Install remote/jumper cable in Fuse 17 terminal -2- and positive (+) remote connection in engine compartment.
Disconnect vacuum hose from fuel pressure regulator.
Must be: 4.0-4.2 bar (58-61 psi) with fuel pump running
Must be: 3.4-3.7 bar (49-54 psi) immediately after fuel pump (remote control) is switched OFF.
Note:
If fuel escapes during the following pressure check of vacuum connection at the fuel pressure regulator, replace the regulator."
Hope this helps somebody.
Dave F
Last edited by UrS4boy; 05-25-2009 at 10:04 PM.
