Hey guys I have a new issue. When you flick the fuel pump on (its close to the tank) there is a hissing noise in the engine bay which I think is fuel going fast through the return system. The first time you start the truck is it very hard to start. If you flick the key it will fire once then crank. If you flick the key off then back on again it will fire once more then crank. If you do this quickly (on off) about the 10th to 15th time it fires it will splutter into life but only just. Once it has started once it will start with a flick of the key unless you leave it for a while.
If I crimp the fuel return line the hissing noise stops and the truck starts first time. (or so the testing I have done so far shows could have been a bit flukey, will test again tomorrow)
Questions
how does the return system work?
should there be pressure in the return pipe when truck isnt running? (if i pull it off the steel return line and flick the pump on there is alot of pressure)
is it bad If i block off the return pipe?
5m fuel system. Faulty return valve?
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Landy Rover
- Hard Yaka
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- Joined: Fri Dec 12, 2008 12:11 pm
- Location: Feilding
Re: 5m fuel system. Faulty return valve?
I would say a faulty presure regulator, ie stuck open which will make it hard starting as not enough presure in injector rail. Think they're just bolted on with an O ring.
S3 Rover truck cab, injected 186, Sals rear,Toyota P/steer, Safari disc brakes front, R/Rover D/brakes rear, 9500 winch,twin optima batts, roll bar, Disco seats, 33" JTs, scene lamps, onboard air, Front ARB locker.
Re: 5m fuel system. Faulty return valve?
Right I've been doing some thinking thismorning and this is my understanding of how the sytem works...
Fuel pump pumps to a certain pressure where it will cut out and hold that pressure (for argument sake lets say 80psi, just a guess) this pressure is now in the fuel rail up to the fuel pressure regulator. My understanding is that the FPR is there to release pressure if the pressure cut out on the pump fails to opperate so FPR will release at a higher pressure than the pump cut out (lets say 100psi). If the FPR sticks open there is a restriction "j-pipe" in the ruturn line that will restrict the flow back to the tank just enough that the engine should be able to run to limp home (lets say 40psi or something).
My guess is that my FPR is often sticking open and the restriction in the jpipe is all that's allowing the engine to run.
The only disadvantage to blocking off the return pipe would be that you are effectively putting in a FPR that when it realeases will pop a hose off and piss fuel everywhere at high pressure... But this will only happen if the pressure cut out on the pump fails to operate.
Is this correct??
Fuel pump pumps to a certain pressure where it will cut out and hold that pressure (for argument sake lets say 80psi, just a guess) this pressure is now in the fuel rail up to the fuel pressure regulator. My understanding is that the FPR is there to release pressure if the pressure cut out on the pump fails to opperate so FPR will release at a higher pressure than the pump cut out (lets say 100psi). If the FPR sticks open there is a restriction "j-pipe" in the ruturn line that will restrict the flow back to the tank just enough that the engine should be able to run to limp home (lets say 40psi or something).
My guess is that my FPR is often sticking open and the restriction in the jpipe is all that's allowing the engine to run.
The only disadvantage to blocking off the return pipe would be that you are effectively putting in a FPR that when it realeases will pop a hose off and piss fuel everywhere at high pressure... But this will only happen if the pressure cut out on the pump fails to operate.
Is this correct??
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Landy Rover
- Hard Yaka
- Posts: 263
- Joined: Fri Dec 12, 2008 12:11 pm
- Location: Feilding
Re: 5m fuel system. Faulty return valve?
OK, the presure regulator is there to maintain a presure of approx 35psi with engine running. It has a diapham and preset spring inside and also a vacum line that under normal driving the vacum holds the valve open enough to maintain that 35psi. When full throttle is given, vacum decreases and therefore allows the valve to close a little more increasing the rail presure to approx 40-42psi. Blocking off the return line will raise the presure in excess of 100psi which will eventually destroy the pump and possibly damage the injectors not to mention piss poor fuel economy, so dont block it off. A sec-hand regulator from auto wreckers shouldnt be much over $50 and possibly one from another Toyota vehicle car whatever may fit.
S3 Rover truck cab, injected 186, Sals rear,Toyota P/steer, Safari disc brakes front, R/Rover D/brakes rear, 9500 winch,twin optima batts, roll bar, Disco seats, 33" JTs, scene lamps, onboard air, Front ARB locker.
Re: 5m fuel system. Faulty return valve?
cheers mate that makes sense much appreciated