Thio

Hi everyone

My dad and I are working on a 1979 Porsche 928 Euro 5spd and we tried to start the car, but the car would not start. When we turn the ignition key to the on switch, we hear a big "clunk" in the rear, but no hissing sound.

Could the sound come from the fuel pump? And if so, what is wrong with it?

Thanks a lot for helping

Thio

Randy V

Hey Thio, welcome aboard!

Yes, it very well could be a frozen fuel pump. The fuel pump is located at the right rear of the car.

The simple way to test for fuel pump action is to turn the ignition key just enough to engage the starter motor for a 1/2 second, then release the key. You should then be able to hear a hum or buzzing noise from the right rear of the car that will last for 1-2 seconds, indicating the fuel pump is operating.

Alternatively, you can remove the fuel pump relay and jumper across points 30 and 87 to engage the pump.

Here's a link to the fuse/relay locations for your '79 model, courtesy of 928 Specialists:

http://www.928gt.com/928specs/78-79relay.htm

If the pump seems to run OK, you may have a bad fuel pump relay.

Also, check and replace fuse 22 for the fuel pump.

Gregg K

Howdy!
First post is a quiz.

The fuel pump is pretty easy to get out and analyze. You can even jumper it to a battery once it's out. If it spins, then it's probably ok. If not, it's either got junk in the vanes or bad brushes, or just dead. I've forgotten if these pumps can be pulled apart and massaged, but I'm guessing that even if it's gunked up, it can be disassembled and cleaned. It could be stuff in the tank that has clogged it. But I could be totally wrong about all of this. I pulled my 79 pump and it took about 30 minutes. The only thing to be careful of is to make sure to be ginger with the electrical terminals, as they can break or twist. Otherwise, I can't imagine, off hand what the clunk would be. Maybe the accumulator. But I think the car will start with a bad accumulator.
Hope this helps. And welcome to a great place for 928's.

Gregg

Dennis Wilson

When the pump on my 931 went clunk (sat for 6 years) I tried jumping the relay and fried the windings. I would try taking it off and spraying cleaner through it to remove any possible blockage. You could also try reversing the polarity on the wires to see if it will push the blockage back out. BTW never dry run the pump for more than a few seconds as the fuel is the only lubricant for the motor.

Dennis

Jumpydude

Hmm, not sure about the clunking but recently, I was stuck in bad traffic for like 2 hours... maybe factor that in with really hot temperatures, I began to hear a buzzing sound coming from the back. When I got home, it was still buzzing and appeared to have come from the fuel pump area... it hasn't done that since so I wonder why it was doing it that day. Maybe my fuel was overheating or honey bees got in my tank?

Thio

Thanks for the replies

My dad and I will try to either rebuild or just get a new fuel pump when we have the chance.

I will post results as soon as the car runs

Thio