Rear mounted fuel pump

[BLD]

I have an early 70's car with a rear mounted fuel pump which has failed. I have bench tested both a Bosch replacement and a GSF pump and both flow at 1.5 litres in 25 seconds. On fitting each pump in turn to the fuel lines neither pumps fuel when asked. There is a free flow of petrol along to the pump inlets but neither pump pushes fuel from it's outlet into free air. Can anyone explain this odd behaviour - perhaps I have missed the blindingly obvious.

Any suggestions most welcome.

 

[Robin]

You do not say whether your car is a mechanical injection fuel pump which has three pipe connections and is a long suck short blow type of pump with a return to the tank pipe to return fuel when the injection pump block is full. The fuel pumps are roller cam type of pumps and will stop when the smallest speck of dirt gets into the rollers. You should check that the pipes are clean and free from any dirt and make sure the fuel filter(s) are clean and not blocked or renew them. If yours is the three pipe pump then make sure the pipes are on the right way round, one pipe is a smaller diameter but the other two can be mixed up, the pump works while the tank is full but will stop when it gets to half full. Good luck.

 

[BLD]

Robin
The car is fitted with MFI. One inlet, one outlet only. The return line is separate.
It is strange that both pumps are satisfactury when bench tested. The fuel filter is in line after the regulator as normal. Correct me if I am wrong, but one would have thought that Porsche would have fitted pumps that were tolerant to a tiny bit of dirt as no filter was fitted between the tank and pump, at least not in my car.

 

[Nick Moss]

The correct MFI pump has 3 inlets/outlets: Supply, Delivery and Return, marked S, D and R respectively

 

[Nick Moss]

 

[BLD]

Nick
Am I correct in assuming the pump you illustrate is the £500 plus one? This car is non-standard in many respects and was fitted for a short while with a GSF pump which their catalogue indicates is suitable for rear mounted and MFI examples. The return by-passed the pump (not my fitting I might add). The intention is to replace the GSF pump.

Put in simplest terms, the pumps pump fuel on the bench, in place the fuel flows to the pump inlet, the pumps operate but do not pump fuel either into free air or to the regulator.

HELP !!!!!

 

[Nick Moss]

Correct me if I am wrong, but one would have thought that Porsche would have fitted pumps that were tolerant to a tiny bit of dirt

Well they did, so my advice is to fit a correct pump.

 

[Alex Postan]

I have had similar problems that have resulted in the purchase of two (found to be unnecessary) pumps over the years. The first time it turned out that a well known independent had connected the feed to the return and the second time some chassis welding by the same "specialist" ended up collapsing the non metallic fuel feed pipe in the "transmission tunnel". The third onset of vehiculus stoppatus was caused by the brass gauze filters in the tank becoming blocked with dirt and solidified petrol. Francis Tuthill and his crew solved it. Makes his prices look cheap when they produce results.
Lift the tank out and clean it out and remove the unions and filters from the tank. Replace the feed and return pipes and replace all the fabric covered rubber pipes in the engine bay.