MFI Pump - Fuel Connections

[billytan]

Hi,
Am restoring a 1973 2.4E. Car can start, idle, does not accelerate well, backfiring, jerking quite badly but will eventually cruise quite strong at 100 kph. I finally inspected the fuel line connectiond from the Fuel Filter Console to the Bosch MFI pump and compared it to a 1972 2.4E I have that is running very well.
On the car that is working well, the Fuel Supply line is connected to the FRONT RIGHT Nozzle of the pump, and the excess fuel return (to Filter Console) is from the nozzle at the LEFT MIDDLE part of the pump body. On the car that is not working well, these were REVERSED - Fuel supply into the LEFT MIDDLE part of pump body Nozzle, and return from the RIGHT FRONT Nozzle.
I just queried my mechanic on this and he says that:
1.The inlet and outlet nozzles can be revered for different MFI pumps (both cars are 2.4Es, one year apart in manufacture)
2. That if the fuel lines are wrongly connected, the car will not start, idle or run

My question:
1. Is it correct that the inlet should be RIGHT FRONT and excess fuel return from the LEFT MIDDLE Nozzle?
2. Is it rubbish (or true?) that these may be reversed for different pumps?
3.Is it possible for the connection to be wrong but for the car to still be able to start and run (but not well) because some fuel is still getting to the pump from the fuel input at the return nozzle?

I intend to re-connect the lines tomorrow and would rather be sure, than do by trial and error.

Much thanks, Billy, Singapore

[Grady Clay]

Billy,

Here is the problem (post #17):
MFI Fuel Starvation...Out of ideas.....help please
and
MFI Problems
(2004 threads)

Porsche published a wrong diagram and 'slipped-in' a corrected version, never acknowledging the error.

Best,
Grady

[billytan]

Grady,
Thanks for coming to the rescue again, so quickly too. Much, much appreciated.
In my car, even the connection to the Bosch MFI pump itself seems wrong- Fuel supply entering to the left rear nozzle, and excess fuel return via the front- right nozzle. In the diagrams you gave , and on my other car, its the other way. Supply to right-front nozzle, and return via left rear nozzle.

Now I realise that the fuel filter console connection is also wrong. It's as in the "wrong diagram", with fuel from the electric pump entering via the left nozzle (my left when facing the filter console). On this car, the nozzle on the right side had been blanked off, and the return from the MFI pump is entering via the CENTRAL nozzle (meant for return to the fuel tank)!

Amazing how these "professional" mechanics do their jobs.

Much thanks, will do the rectification the next few days.
Regards, Billy

[Grady Clay]

Originally Posted by billytan

...
Amazing how these "professional" mechanics do their jobs.
...
Regards, Billy

Billy,

This is difficult to entirely blame on your mechanic.
Porsche K.G. published the “wrong” version in both Christophorus and the 911 Workshop Manual.
In a later supplement to the Factory manual, they included the correct version as a ‘replacement page’ with no explanation of the obvious error.
The error in Christophorus was never acknowledged.

Before the correction, I made the error putting a MFI engine (2.2E) in a new ’70 914-6.
It took me looking at another (original) MFI 911 as I had already replaced the hoses with new - per the Factory (wrong) diagram.

This error shouldn’t have been propagated to today. After all, it is only 40+ years.

Best,
Grady

[cmcfaul]

A Pic of how it is connected would help a lot. It is easy to connect the lines going to and from the fuel filter incorrectly.

Chris

73 911 E

[Grady Clay]

Chris,

Go to the above links.
It is all explained very well there.

Best,
Grady

[cmcfaul]

Yep, your diagram is right on. The hoses are counter intuitive as to their connection. The way they look like they should connect is not the correct way. The car will run in either scenario but does strange things when not connected correctly.

Chris
73 911 E

[Eddyvdw]

Hope you guys can help me out.

Did a top end restoration. Refitted everything and I'm sure I have the fuel hoses right. Spark is also ok. Still no fuel from the MFI pump with disconnected (hard) fuel line in a jar.

How long do I have to crank to get some fuel in the cylinders?

Thanks,
Ed

[tobluforu]

When you turn the key to the on position you should here the pump turn on, (not the cd whine). You should then hear the fuel circulating through the tank. Do you here this, if not then I suspect your pump.

[Eddyvdw]

It's official, I'm an idiot. Tank was completely empty, the fuel I got was the little bit left in the lines....

Quickly to a gas station, hope this was the problem ;-)

Ed

[Eddyvdw]

Refueled, still no gas at at the injectors.

Hmmm, running out of ideas.

Bottom line of the filter is connected to the inlet of the MFI pump. The return line form the MFI pump gives a nice steady flow of fuel.

Timing of MFI pump is spot on. New belt. turns nicely.

What to check as well?

Thanks,
Ed