Bosche type fuel injection return line 1

[thruthefence]

I'm converting a 'carb' car to EFI (Toyota) and need to add the fuel return line to the tank. Every one I have seen has entered from the top of the tank (along with the fuel pump line & fuel qty wiring). This may be an 'ease of manufacture' feature I suppose.

Any reason I cannot enter the tank below the fuel level?
I have a fitting that would be convenient to use, but it sits at about the 1/4 mark on the tank, which is tall & narrow, and about 10 gallons capacity.

 

[thruthefence]

The original Renault engine (carb) had a fuel return line from the mechanical fuel pump to the very spot I am considering; the fuel quantity transmitter. After reading the remarks on terminating the fuel return inside the baffled 'sump' I may reconsider the routing.

If someone could advise me how to ink to a picture, I will post the 'lash up' of the components.

thanks, Steve

 

[Tmoose]

By "swinging gate" do you meant this L-jetronic

http://www.pelicanparts.com/catalog/images/docs/bosch_fuel_injection_1_sample.JPG

or, K-jetronic

http://carburetor-manual.com/images/Bosch-K-Jetronic-1.jpg

I sort of recall the "control pressure" for K-jet mechanical Bosch injection being somewhat higher than the electronic types. It's set by the regulator, not the pump, but I'd wonder about possible differences in pump suitabilities.

Dan T

 

[thruthefence]

It's the stock Toyota system, very similar to the Bosch L-Jetronic system, probably licensed from them. There is an IAC valve for idle control, and no cold start injector.

Technical information on the (Yamaha designed) 20 valve cars is hard to get, so I didn't really have specs for the pump. It was chosen on availability, price, and intuition. (I felt if it would supply a 190 HP engine, it should be ok for my 135HP.)

 

[WGJ]

If the Toyota-system pump looks like this:

http://images.imagelinky.com/1232920653.jpg

..and it's about 52mm diameter,
then it's probably a JECS pump which is a licensed/copy/rip-off (whatever) of the Bosch L-Jetronic.

The common L-Jet pump was rated at 130litre/hour at 3 bar and was used on a variety of system pressures from about 2.5 to 3.5 bar with consequent differences in flow. Current consumption of a bedded-in pump at 12 volts is about 3.5 amp at 3 bar.

Bill

 

[thruthefence]

Does anyone know if the pressure/volume of the return line fuel would be enough to drive a 'jet pump' capable of transferring fuel into the baffle pan? Any literature on design?

At some point in time I may add a second fuel tank, and was thinking this may be a simple way to keep the main tank (where the pump & fuel qty Xmitter are located) more or less topped off.

I'm thinking the return flow may just be a 'dribble', without enough horsepower to do any work.

 

[LionelHutz]

The C5 Corvette has 2 tanks split on each side of the car with a crossover tube at the top. They use the return fuel from the pressure regulator plus the veturi effect to transfer fuel from the tank without the pump to the tank with the pump. Works fine unless the orifice gets plugged.

 

[WGJ]

Thruthefence, may I refer you to a couple of patents on jet pumps?
In-tank fuel supply unit US2003000502
A fuel delivery system EP1302354

There are sketches on these relating to what a commercial, high performance jet pump arrangement ought to look like for both single and 'saddle' or dual tank arrangements.
Blowing my own trumpet, I designed these for the Jaguar X400 and X350 projects, although the customer was ultimately unhappy with the costs that my incompetant employer quoted and never used them.
We used them and they worked better than expected - would support over 500bhp.



Wit a jet pump on the return side of the system, you are limited as to the size of the JP nozzle.
As the flow of return fuel varies (lowets at full throttle, highest at idle/part throttle) so will the reservoir filling capabilities of the JP.
If you limit the return line pressure to, say 30kPa/4PSI, at maximum return flow, that should be fine.

You could just use the natural diameter of the return line and use that to drive a pretty basic device - a combination of a reservoir and the so-called 'swirl pot'.


Bill

 

[WGJ]

See if this pic makes sense:


Bill

 

[thruthefence]

Just to follow up, I ended up entering the tank through my adapter plate at the top of the tank (rather then below fuel level, as originally envisioned), using an AN bulkhead fitting. I ran a line (#4 AN, approx 3/16 " ID) down to the baffled tank, and terminated it just barely inside a flared AN #12 (appox 13/16" ID )tube that passes through the wall of the baffle tank. Idea being to act as a crude aspirator, or jet pump, to help keep the baffled area (and the fuel pump inlet sock)topped off with fuel. This is similar to the pic WGJ provided. Thanks to all for the advice.

 

[WGJ]

Hope it works well.

Bill