MFI Fuel Pump Question

jbell959 · 11-16-2006, 06:11 AM

Does anyone know the specs of the 914 Fuel Pump (Bosch # 580 463 005)? I was told that this pump has the same specs as the 911 MFI pump (Bosch # 580 970 001).

Cheers,
John

304065 · 11-16-2006, 06:27 AM

914 fuel pressure is 2 bar.

911 MFI fuel pressure is 1 bar, relief valve opens at 2 bar.

If you use the 914 pump you will run too rich. MFI tends to run rich as it is, I would stick with the correct pump to make future diagnosis easier.

jbell959 · 11-16-2006, 06:33 AM

Thanks John

Zeke · 11-16-2006, 06:52 AM

Ssems like there'd be a way to rig a fuel pressure regulator in the loop. I'll bet 914 pumps are more plenttiful and less money in that they were probably used on a million VW's.

jbell959 · 11-16-2006, 06:56 AM

They are about 1/2 the price new and I would also bet they are much easier to find used.

BURN-BROS · 11-16-2006, 07:55 AM

John,
Any fuel pump can be used to supply fuel for mfi fuel pumps. The mfi injectiom pump really only requires volume. The preassure is regulated by the check valve in the fuel station(fuel filter housing). Supertec has used cis fuel pumps for years on custom displacement mfi and 700 hp 935s ran a cis style fuel pump producing 5 bar of preasure.

304065 · 11-16-2006, 08:44 AM

Aaron,

I can understand the need for high pressure in a 935. However, my own experience, and Grady's experience in the below thread suggest that high fuel pressure will affect the mixture. I have a Walbro in-tank pump in my fuel cell that will deliver 5 bar in the return line, but I deliberately dial it back with an adjustable fuel pressure regulator to 1.0 bar so I don't tear my hair out during diagnosis.

What PSI does an MFI FUEL pump (not injector pump) put out/need?

I have never cut open a fuel filter console but my recollection from looking at one is that it's just an open plenum. But perhaps you've been inside one? That would be cool info up there with the mysterious "flow restrictor" that's supposed to be in the return line, which many claim exists, but like the Snuffleuffagus, few have seen!

In any case, here are the pump specs.

Clay Perrine · 11-16-2006, 09:23 AM

In the MFI fuel console there is a pressure regulator. It is contained the the banjo bolt that feeds the return line.

Ask me how I know.....

I hooked up the MFI console backwards on my 914/6 conversion. Spent hours beating my head against the wall trying to figure out why I didn't have any fuel flow to the injection pump. I had the pressure regulating banjo bolt in the incoming side of the filter console. Once I got that working, I had to figure out why there was no pressure. I didn't put the pressure regulating banjo bolt in the outlet side.

Plus, I had not reversed the picture of the 911 mounting, so I was hooking up the lines backwards.....

BURN-BROS · 11-16-2006, 06:36 PM

Hi John(Cramer),

I was not implying that you use all the pressure of the pump, The internal checkpoint should take care of this. If the car was carb'd or cis originally an adjustable pressure regulator would be in order (just as you did with the Walbro). The cis pump if you look around can be had very reasonably.

Thanks for the link, lots of good info from Grady as usual. I can understand a lack of volume being a problem, but it's hard for me to reason out why excessive pressure is a problem. I will take your word for it. If someone has the reason please P.M. me