914-6 w/2.4 '72 911 "T" motor, MFI

The previous owner of my car (let's call him "Bubba") installed a regular plastic in-line fuel filter between the tank and the fuel pump. The factory fuel filter is upstream (between fuel pump and injector pump).

Is this "pre-filter" necessary? Looks like one big fuel leak waiting to happen.

no bigger leak potencial than the single filter i run upstream from the pump on my car. why would you want to suck all of the crap out of the bottom of the tank thru the primary pump?

k

I dunno. The filter that the P.O. installed doesn't look like it belongs there. Did Porsche have a filter in-line between tank & pump?

The filter is supposed to be between the Fuel tank and fuel pump.

What's an injector pump?

The belt-driven pump that sends the fuel (under pressure) to the fuel injectors:



In my car, there is a fuel filter immediately before the injector pump.

Iv'e never seen anything like that before.

What motor? what year?


Why would there be a second pump for the fuel inj's.? do they run at an extreemly high pressure?

Are you sure that's not an air inj. pump for smog?

Motor is a 1972 2.4 "T" motor from a 911 (see first post).

The fuel injection pump sends fuel to the injectors upwards of 200psi.

I am 100% certain that is not a smog pump. It is the injector pump.

Bubba is a pretty smart guy.

Personally, I like a filter between the tank and pump to filter out crap. That way, the crap can't chew up the expen$ive pump. When the pump is running, it is sucking fuel from the tank and the line is at a small negative pressure and unlikely to leak. When the pump is stopped, there is only a small amount of head pressure from the weight of the fuel, and worst case is a drip.

After the pump, you have PRESSURE. And when the pressure side leaks, it is much more spectacular, particularly when the jet of pressurized fuel hits something hot or electrical....

Ken

For stock applications, I recommend (and use) a metal filter from a 2002 Tii (13 32 1 256 492, or Bosch # 71 015). 8mm inlet and outlet. You should also have the special 10mm>7mm adapter hose from the plastic line to the filter (914 356 525 00). A bit costly, but it FITS. Spend a little money here, and you'll lessen the frequency of changes of the astronomically expensive MFI filter. The Cap'n

Not when he uses a plastic filter that hangs down under the car and secures it only with (cheap) hose clamps.

Thanks for the advice. Seeing the other (canister-type) filter upstream, I figured the pump only "passed-through" the fuel and didn't require filtering. The "Bubba Job" looks home-made and hence, suspicious.

Where does this adapter hose fit into the system? Again, I have a 2.4 MFI system, including the fuel pump. The hoses appear to all be the same size where they come through the firewall (from the tunnel) and go to the pump. I'm not sure where the size reduction is.

Yes, the MFI filter is $59...

The hose fits at the end of the plastic line after it comes out of the body and makes its turn to the right. IIRC, the line on the six is the same as the one on the four. The hose allows you to safely attach the 8mm in/8mm out filter to the line. From the filter, a 7mm hose goes to the original fuel pump. As the pump that supplies fuel to the MFI system is visually the same as the EFI pump and the pump for carbs, it should be plumbed in the same way. The Cap'n

Bubba's real name is not important.
But we all know and hate him for something.
DAPO is the term some of us use.

Dumb Ass Previous Owner.

The goal is to not become one yourself.

I use a coarse filter from the fuel tank to pump and a micron filter before the carbs. Ya never know when you might get a crud burst from a gas station pump or a shot of water. Worst time to buy gas, right after they fill their tanks, stirs everything up.

Agreed. with stirred up under ground tanks.