Fuel Pump Troubleshooting (long)
06-08-2001, 09:46 PM
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Rennlist
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Rennlist
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Fuel Pump Troubleshooting (long)
I was asked on the rennlist 911 email list about fuel pump trouble shooting. Thought the answer might be of interest on this forum. Scenerio is 1980 911SC owner who thought he wasn't getting any fuel to the engine:
First, try this. Take the top of the air filter off as well as the air filter. Put the key in the ignition, turn it on, but don't crank the engine. Go back to the air intake, reach in (if you get down low you'll see a round metal plate with a curved metal piece attached to it). Push the metal plate up 1/2" to an inch. If you're fuel pump and relays are working, you'll hear all sorts of chatter starting up, which are the injectors being pumped full of fuel. No sounds at all? Go back and turn the ignition off. In the front compartment where the relays are, the red relay is your fuel relay, and it has a special diode in it that the black one's don't have. If you don't have a spare red relay (I carry a spare), pull the red relay out and look at the pins. You'll see that they are split. Get a knife and open up the pins just a little bit. Push the red relay back in, and repeat the key in ignition and lifting of the round plate in the air cleaner. Often, that does the trick. The relay an look plugged in, but if it's out just a bit, it doesn't work. Still no chattering noise? Back to the red relay. Pull it out. See on the bottom it has numbers on it. Get yourself a switch and some wire (and for saftey you ought to put a fuse inline with it). With the switch off, stick the wires in the 30 and 87a holes that the relay would have gone into. Turn your ignition on, turn you makeshift tester switch on, back to the round plate in the air box. Lift it again. Noise, then bad relay. No Noise, likely bad fuel pump.
If you do your own work, jack up the front end, drop the steel plate under the steering gear area, and with the ignition on and makeshift tester switch on, check for voltage at the fuel pump terminals. This will just confirm it's getting juice. If it's dead, you'll need to replace it. I also recommend you replace the two rubber bumpers that isolate it from the body. The fuel pump makes quite a racket when they break, and if you're going to take it apart, you might as well renew the rubber pieces. When I replaced my pump, one was broken, so I replaced both. Putting the new pump in is straight forward. You'll need a good clamp on the short hose coming out of the tank. Expect to spill some gas on you. If you're good, not alot. You may also want to renew the big adjustable clamp that holds the fuel pump to the bracket that is attached to the body. The fuel cap nut was really rusted on mine, so I put a new one on while there. Probably didn't need to, however, you know if I didn't have a spare the old one wouldn't have come off
. Porsche part number for a new fuel pump is 911.608.102.02. I paid around $197 from Hendricks Porsche at 800-315-8193 (no affiliation, just satisfied customer).
First, try this. Take the top of the air filter off as well as the air filter. Put the key in the ignition, turn it on, but don't crank the engine. Go back to the air intake, reach in (if you get down low you'll see a round metal plate with a curved metal piece attached to it). Push the metal plate up 1/2" to an inch. If you're fuel pump and relays are working, you'll hear all sorts of chatter starting up, which are the injectors being pumped full of fuel. No sounds at all? Go back and turn the ignition off. In the front compartment where the relays are, the red relay is your fuel relay, and it has a special diode in it that the black one's don't have. If you don't have a spare red relay (I carry a spare), pull the red relay out and look at the pins. You'll see that they are split. Get a knife and open up the pins just a little bit. Push the red relay back in, and repeat the key in ignition and lifting of the round plate in the air cleaner. Often, that does the trick. The relay an look plugged in, but if it's out just a bit, it doesn't work. Still no chattering noise? Back to the red relay. Pull it out. See on the bottom it has numbers on it. Get yourself a switch and some wire (and for saftey you ought to put a fuse inline with it). With the switch off, stick the wires in the 30 and 87a holes that the relay would have gone into. Turn your ignition on, turn you makeshift tester switch on, back to the round plate in the air box. Lift it again. Noise, then bad relay. No Noise, likely bad fuel pump.
If you do your own work, jack up the front end, drop the steel plate under the steering gear area, and with the ignition on and makeshift tester switch on, check for voltage at the fuel pump terminals. This will just confirm it's getting juice. If it's dead, you'll need to replace it. I also recommend you replace the two rubber bumpers that isolate it from the body. The fuel pump makes quite a racket when they break, and if you're going to take it apart, you might as well renew the rubber pieces. When I replaced my pump, one was broken, so I replaced both. Putting the new pump in is straight forward. You'll need a good clamp on the short hose coming out of the tank. Expect to spill some gas on you. If you're good, not alot. You may also want to renew the big adjustable clamp that holds the fuel pump to the bracket that is attached to the body. The fuel cap nut was really rusted on mine, so I put a new one on while there. Probably didn't need to, however, you know if I didn't have a spare the old one wouldn't have come off
. Porsche part number for a new fuel pump is 911.608.102.02. I paid around $197 from Hendricks Porsche at 800-315-8193 (no affiliation, just satisfied customer).
