1975 Rabbit Mechanical fuel pump

[srgtlord]

So I started thinking, what if I wanted to rid myself of the electric fuel pump on my diesel when I get it running again someday. Why couldn't I just slap on a mechanical carb pump from a 75 rabbit on the diesel block and call it a day?

[vanbcguy]

Assuming you have added an electric fuel pump to your car? There isn't one there stock.

The hard part would be finding a mechanical pump that won't degrade with diesel fuel. The rubber diaphragms used in a lot of gas pumps aren't usually rated for diesel.

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[ORCoaster]

Plenty of us run every day without an electric assist pump.  The VE works just fine. 

[rabbid79]

Since it's a '75 I'm guessing it was originally gas.  I don't think diesels were introduced until around '78.  Still though, being a gas car it wouldn't have been CIS in '75, so I don't understand why it would have had an electric fuel pump.

[vwnut84]

First VW diesels were 1977 model year.

[8v-of-fury]

So I started thinking, what if I wanted to rid myself of the electric fuel pump on my diesel when I get it running again someday. Why couldn't I just slap on a mechanical carb pump from a 75 rabbit on the diesel block and call it a day?

I am pretty sure the lobe to run the mech pump is not present on the diesel IM shafts. Which turn opposite rotation of the gas ones anyway. Gas timing belts go out and ride on the IM pulley, diesels serpentine around it and use the back of the belt to run the IM shaft pulley.

[burn_your_money]

I am pretty sure the lobe to run the mech pump is not present on the diesel IM shafts. Which turn opposite rotation of the gas ones anyway. Gas timing belts go out and ride on the IM pulley, diesels serpentine around it and use the back of the belt to run the IM shaft pulley.

It does have the lobe, it's what everyone gets to excited about shaving off and balancing. As for it running the opposite way that isn't an issue as the check valves in the pump manage the direction of fuel flow.

[srgtlord]

So I guess the answer is it "would" work but longevity may be an issue due to the construction of the diaphragm? Hmm I read something about carter pumps being updated to combat ethanol degradation. I will have to do some digging around on the net...

[8v-of-fury]

Just curious.. why you are against a 12v electric?

[srgtlord]

I have nothing against the electric pumps, just thought it would be an interesting idea and possibly another solution

[8v-of-fury]

Plenty of us run every day without an electric assist pump.  The VE works just fine. 

Truth, but a 12v pusher is a fantastic thing .

[bajacalal]

I've always wondered why our cars don't have an auxiliary fuel pump besides the IP... On a Cummins diesel, with the same injection pump, it has a mechanical fuel lift pump, and it's considered a necessary part. Why can the VW get away without using one?

[8v-of-fury]

I think it is because they use the same size lift pump internally, but are then required to pump out quite a bit more fuel? Much larger fuel lines? Longer distance to run?

They have the 12mm plunger pumps, so I am guessing they move A LOT more fuel and you could probably idle the engine without a lift pump but if you needed more fuel on demand it may not be there.

[JamesT]

Less possible height to lift. A truck with a Cummins can have 8 feet height difference or more between the tank and the pump if parked on a hill.

A carb pump only has to keep up with peek engine fuel demand. A diesel pump is a constant flow type, so a lot more fuel needs to go through than what the engine will use.

[hillfolk'r]

Id try a mech fuel pump for giggles. I dont think the fuel is gonna hurt the mech pump