Bosche type fuel injection return line
Bosche type fuel injection return line
(OP)
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.
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.





RE: Bosche type fuel injection return line
Just some ideas I had.
RE: Bosche type fuel injection return line
RE: Bosche type fuel injection return line
this will surely "simplify and add lightness" to the project.
thanks, Guys
RE: Bosche type fuel injection return line
Good practice in many industries includes no penetrations in any surface other than the top of fuel tanks, probably because of historical problems with reliability of tank wall penetrations, and the consequences of leaks.
Mike Halloran
Pembroke Pines, FL, USA
RE: Bosche type fuel injection return line
RE: Bosche type fuel injection return line
My reasoning agrees with Mikehalloran. Potential for leak at the skin fitting.
Regards
Pat
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RE: Bosche type fuel injection return line
RE: Bosche type fuel injection return line
The only other concern I would have is if the vehicle is old enough to not have a carbon canister, and pressure could build in the fuel tank on a hot day due to fuel heating, would it be able to push fuel back up the line to the regulator. Even if it did, would this cause any particular harm? It entirely depends on your particular hardware and mechanization, but I doubt it.
-Tony Staples
www.tscombustion.com
RE: Bosche type fuel injection return line
I can't see how the fuel flowing when parked could matter. The injectors are closed so there fuel system is a closed loop from pickup to return fitting with the exception of there being a spring loaded valve (the regulator) in the middle of the loop.
RE: Bosche type fuel injection return line
You are assuming that injectors don't leak when closed. Just the opposite is the case. ALL injectors leak, to some degree, when closed. It's supposed to be very small, but it's there. Injectors utilize a metal-on-metal seal of some type (tapered needle & seat, ball & tapered seat, flat plate over flat seal ring, etc . . .) On a properly functioning vehicle, it should take hours for the rail pressure to leak down after shutting off a vehicle, but the rail pressure will eventually dissipate through the injectors, into the intake.
The concern would be if the backpressure to the regulator would be sufficient to push fuel back into the rail, and keep re-supplying fuel that would then leak out through the injectors. Assuming you could effect enough leakage, and the leakage occured after shutoff on a cylinder where the intake valve happened to be open, then you could, worst-case, fill the cylinder with liquid fuel during shutoff. When you next restart the vehicle, there is a high probability of hydraulically locking the engine during crank. The liquid fuel won't compress, and you then damage a piston or connecting rod.
Ask me how I know.
-Tony Staples
www.tscombustion.com
RE: Bosche type fuel injection return line
And if this is such a dire consequence of a badly positioned return line then why doesn't this type of failure occur more often due to the feed line, which must pick-up under the fuel level at the bottom of the tank???
RE: Bosche type fuel injection return line
As part of my nearly 30 years of experience in the fuel injection industry, at one time I was the Engineering Manager for a company that manufactured regulators for alternative fuels. Similar to injectors, they leak at their metering seats too. Never, ever, assume a regulator is also a shutoff valve at system shutdown.
However, on a modern, FI car, the vapors from the tanks are routed to a vapor canister, for capture, and very little pressure is allowed to build up in the system.
The OP mentioned that he is converting a carb. Toyota to FI. The tank venting properties of older carb. equipped cars was sometimes less sophisticated. Some of these systems allowed a fair amount of pressure to build up before a (typically) fuel cap vent might allow venting. I don't know those details. My whole point is that converting is not as simple as it may seem. What's going on at the tank is different, and not trivially so, between a carb. vehicle, and a FI vehicle. I recommend erring on the side of caution when dealing with fuel systems, especially when you don't have the specialized knowledge of a fuel systems engineer.
-Tony Staples
www.tscombustion.com
RE: Bosche type fuel injection return line
Also, I'm pretty sure excessive built-up pressure in an "old school" tank could also overcome the needle in a carb and cause fuel to either fill the engine or dump all over the intake.
I do agree that the venting of the tank should be investigated and also that odd failures can occur, using either injectors or a carb.
RE: Bosche type fuel injection return line
I've converted my 60's Triumph to EFI and used the tank drain (with short internal upstand to avoid getting all the sediment) to provide flood feed to the high pressure pump and the original fuel line as the return. It works fine. I had a fuel pressure gauge fitted a fuel pressure gauge fitted for quite a while and that showed that the system would hold the 3 Bar running pressure for about 2 hours after switch off before falling away. The leakage was not through the injectors, so must have been through either the regulator or back through the pump NRV. Doesn't matter either way as pressure returns instantly during the 2 second pump prime cycle. All parts were "recycled" junkyard rescues - good stuff Bosch.
Worth mentioning that on some cars, where the tank is low mounted it is sometimes necessary to use a lift pump and swirl pot to provide a reliable feed for the high pressure pump. Some people take the fuel return to the swirl pot rather than the tank although I'm not convinced thats a great idea on a road car that spends time in traffic as the fuel get pretty warm surprisingly quickly. On my car the whole tank warms significantly, although at 8.5 gallons (imperial) it isn't that much bigger than a swirl pot anyway.
Nick
RE: Bosche type fuel injection return line
The car is a 1970 S2 Lotus Europa. The engine is a Japanese domestic market 1.5 ltr 4AGE 20 valve, with the 'swinging gate' airflow meter. Four throttles feeding from a common plenum. The fuel tank is a trapezoid, wide at the bottom, narrow at the top. The Fuel pump, ( a Bosch, with filter sock, from a 2.0 Subaru turbo) sits in a baffle pan of approximately one gallon in the bottom of the tank. It feeds to the top of the tank through a #6 (3/8") aluminum line & AN bulkhead fittings. I have the room (barely) to build a swirl chamber in the tank for the return line, but would like to avoid the complexity. The tank has a 'bung', in it's side, where the original fuel qty transmitter was installed, and I hope to install an aluminum disc, with bulkhead fitting, in this spot, with a #4 (1/4") aluminum tube emptying tangentially against the wall of the tank, which should minimize the 'churning' of the fuel. The 'bung' is approximately 1/3 up from the bottom of the tank.
RE: Bosche type fuel injection return line
I agree that the pressure shouldn't normally build up to too high a point. It really depends on the RVP of the fuel in the tank, and the temps involved. I have seen values of 15 psi and more on certain closed systems, but most most vent below that.
Thruthefence,
Thanks for the additional info. Great car, BTW. However, I would assume, since it's a Lotus, that crash isn't your highest priority. Given that, the side port should work fine as a return point. Just make sure there is some type of venting fuel cap.
-Tony Staples
www.tscombustion.com
RE: Bosche type fuel injection return line
So long as the injectors are not above fuel level when standing and there is no pressure from vapours, and the pump is not running, there is a limited amount of fuel that can leak. The sums are simple and I expect that it will be not that much more than one chamber full.
Aloww for some in each chamber and some time to leak and some evaporation losses and the risk seems small.
Oh hydraulic lock can also blow head gaskets (if your lucky) or the centre out of a spark plug (if your luckier still) or pull or you head bolts, threads and all, out of the block.
Regards
Pat
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RE: Bosche type fuel injection return line
An acquaintance of mine had a problem car, which would stop whenever the tank was at the 1/4 level.
After numerous attempts to correct the problem (at great expense), the last desperate attempt was to break the tank open.
Due to a production mistake, the return line ended outside the baffle pan, which meant that when the fuel level dropped below the edge, the flow was high enough to empty the baffle pan and the car stopped.
A new tank, and the problem was solved.
Benta.
RE: Bosche type fuel injection return line
Venting was direct to atmoshere via a restrictor of about 1mm dia, with the vent continuing via a nylon line of about 4mm ID to a clipping point on the (typically) steel tank somewhere.
Prior to 1993, certainly during the early 80s, FI/EFI derivatives of carburetted models used pretty much the same arrangement as carbon cannisters generally weren't used because legislation did not mandate them.
So - return your fuel to the tank via a 6mm OD (at least) fuel line; enter it via the sender flange and take it down to the bottom of the tank. It always used to work fine.
Bill
RE: Bosche type fuel injection return line
If someone could advise me how to ink to a picture, I will post the 'lash up' of the components.
thanks, Steve
RE: Bosche type fuel injection return line
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or, K-jetronic
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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
RE: Bosche type fuel injection return line
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.)
RE: Bosche type fuel injection return line
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
RE: Bosche type fuel injection return line
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.
RE: Bosche type fuel injection return line
RE: Bosche type fuel injection return line
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
RE: Bosche type fuel injection return line
Bill
RE: Bosche type fuel injection return line
RE: Bosche type fuel injection return line
Bill