Please Verify MFI Routing! It runs both ways!!

[Jandrews]

Hello,

I am trying to diagnose a vibration and power loss situation and I started thinking about the routing of my MFI fuel lines. It seems that the factory manuals and Haynes are in conflict regarding where the supply and return lines attach to the MFI pump.

The trouble is, the dang thing runs both ways!!

I only know this because I switched them!! I have just been marking them and returning them to where they were the last few times I had them off, but I am not perfectly certain where they go. One goes into the passenger side of the pump, and one goes into the front-end side of the pump. It runs reasonably well both ways!! How do you explain that?

I am looking for someone who is abolutely certain about the proper routing. I have ALL the MFI documentation, and don't seem to be able to find one definitive answer. Anyone have an MFI race car or something that runs perfectly who can verify?


Thanks,

JA

[Jandrews]

Ok, I actually drove it today with the lines that go into the MFI pump reversed! It ran identically! Is that normal? I can't imagine how the return line could provide sufficient pressure to keep the volume flowing to the MFI pump. And conversely, having the electric pump pumping fuel into a return line should cause a back-up at a minimum, shouldn't it?

And looking further into the factory manuals, it appears there are pictures in there that actually contradict each other. One page, regarding disassembly of the pump, states "disconnect fuel return line on left side of pump". And there is a picture of a line disconnected that other photos label as "fuel inlet".

Any help or pictures of your MFI pumps and filter console would be greatly appreciated.


JA

[Jim Richards]

JA, this is from my wife's 73E. I'm assuming it's right, but you never know...

[Todd Simpson]

Mine is the same as Jim's. I'll add that the top right outlet that faces the engine goes to the left corner of the engine compartment and the front outlet that faces the front of the car goes to the fuel line through the frame rail.

The Haynes manual is wrong in regards to the routing.

I went through this in my T when I put the S engine in. It will run with it wrong, just not very well.

[Jandrews]

Thanks Jim and Todd.

And by "right" side, I assume you mean as you are facing the engine, i.e. passenger side. Correct?


John

[Todd Simpson]

Yes, right is passenger side, assuming LHD. :-)

[john walker's workshop]

as you found out, it don't matter. there's just a fuel chamber in there.

[Todd Simpson]

There are still other lines you can mess up, between the fuel pump and filter. Get that wrong and the car will run but be starved under load or at high rpm.

[Kevin Taylor]

Could anyone please point me in the right direction for
complete mfi fuel line diagram for 1973 911 E 2.4
I may not have my lines correct from pump to filter.
It stumbles under load.

Thanks K.T.