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What Does The "jet Pump" Actually Do?

DJ-Static

By DJ-Static,
in General Maintenance

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frozenwaffles Mentor

frozenwaffles

Posted
Posted

This 'jet pump' is only ever used/enabled if and when you put Jet Fuel (Jet A-1) in your Skyline...

There is a reason why the taillights look like afterburners you know ;)

Nah in all seriousness I would like to know too!

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blackrex Mentor

blackrex

Posted
Posted

If the jet pump in a Skyline is anything like the jet pump in a WRX fuel tank, then it is used as a venturi effect pump to transfer fuel from the other side of the hump in the bottom of the fuel tank. It works by using the return line pressure to create a lower pressure in the suction pipe, this draws the fuel out of the otherside of the tank and deposits into the side where the fuel pump pick up is. These units are used for a number of reasons in that they are cheap, self priming, very low maintenance and also very cheap. The problems that can occur with them are when you use larger injectors and greater IDC's, there may not be enough pressure and volume in the return line to the tank to drive the pump.

Diagram.jpg

If you imagine that the compressed air is the return line and the vacuum is the line from the other side of the tank, then this give a visual idea of what is happening.

blackrex Mentor

blackrex

Posted
Posted

If you only have a lift pump on one side of the tank (due to the that being siting over the propshaft, there is a hump in the bottom of it) and the jet pump is not working, then you have to rely on the movement of the car to transfer fuel from one side of the tank to the other, so if you are going around a corner and this causes the fuel to move to the other side of the tank to where the lift pump is then it is possible to either not be able to get the full amount of fuel out of the tank, and dependent on the size of your surge tank, the pumps used and the engines fuel consumption, then it could also be drained.

Outlined in Red, is this the jet pump?
attachicon.gifis this a Jet Pump.JPG
Is it supposed to have a hose attached?
(if so, all I had in my tank was what's in the pic.)

If that is the in tank side, then no, they usually just spray into the tank from the nozzle to remove any possibility of flow restriction, the two moldings into it are the return from the fuel rail (center) and lift pipe (outside edge)

scotty nm35 Grand Master

scotty nm35

Posted
Posted

So if I have a lift pump, surge tank and external pump. I shouldn't need it, should I?

Because the external pump performs a similar function.

Correct. Just ditch it.

The Stagea's run these vac generators to suck the fuel over from the other side of the tank too. I didn't think it would be required in a 33 as they run a single tank behind the back seat don't they?

Hanaldo Grand Master

Hanaldo

Posted
Posted

So these can just be ditched? It won't create problems with fuel getting stuck on one side of the tank? I also need to replace the moulded fittings with AN fittings, but I drive around pretty sedately on the streets, so I don't think I'd be doing much cornering hard enough to swish the fuel around...

Hanaldo Grand Master

Hanaldo

Posted
Posted

Ah, just re-read Scotty's post.

So in an R34 with just a single internal fuel pump, I can't ditch this jet pump? What are my options for using AN fittings in place of the moulded ones?

DJ-Static Collaborator

DJ-Static

Posted
  • Author
Posted

This is my plan:

post-59520-0-18904500-1377426993_thumb.jpg

I think I made a few slight changes since making the jpg, but that's the crux of it.

I plan on making a full DIY write up. From what I can tell there isn't one out there (hence threads like this)

Hanaldo Grand Master

Hanaldo

Posted
Posted

I understand the majority of the plan, but still not quite sure what you are doing with the fuel lid. Are you just using the one AN bulkhead fitting and keeping the plastic return fitting? This is what I think I am gonna have to do, though I'd prefer not to...

I have also thought about using a Speedflow tube adapter to convert the plastic fitting to an AN fitting. This would maintain the jet pump setup, AND allow me to run PTFE hose. The only thing is, the plastic fitting is an odd design and might not work with the tube adapter.

blackrex Mentor

blackrex

Posted
Posted

The 040 and 044 pumps are not E compatible according to Bosch, having said that, there are a large number of cars that run them (mine included) that do not seem to have an issue.

A solution to this could be two separate lift pumps (such as these http://www.efihardware.com/products/261/lift-pump-340hp-Rollercell) drawing from each side of the tank using the pickup for the lift pump as well as the standard pickup.

DJ-Static Collaborator

DJ-Static

Posted
  • Author
Posted

I'm sure they say that because E85 kills a lot of pumps due to the crud it stirs up.

Pump comes back. Pump comes back. Pump comes back. Then the quality manager for Bosch goes "put on the package we don't warrant returns for E86 anymore".

This is overkill for a lift pump to a surge tank. But it's probably the best in tank pump for E85:

http://www.sonicperformance.com.au/F90000267/Walbro-Fuel-pump-Intank-E85-450lph/pd.php

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