I dont recall ever seeing the answer to this on the forums, so here it goes. Does the LNF finally have a return style fuel system? or is the DI a returnless fuel system as well...

 

returnless

 

What is the benefit of the return system? I notice a few LSJs adding it.

 

i believe its so you dont blow the #4 when heavly modded

 

on a return style system, the pump will supply say 60psi of fuel to one end of the fuel rail, and there will be a sensor at the other end of the fuel rail to ensure there is still 60psi of pressure before the remaining fuel that was not used in the injectors returns to the fuel tank. On a return-less style, there is nothing after cyl #4, so its very possible for cyl 1 to have 60psi, cyl 2 to have 60psi, cyl 3 to have 60psi, and cyl 4 to have, say 55psi, as all the fuel would have entered the first 3 injectors and not enough remains to enter the 4th at the same value.

At the end of the day, it can lead to uneven distributions of fuel for each cylinder...making it a bitch to tune, since widebands will show the average AFR for all 4 cylinders, instead of showing cyl 1 runs 11.5:1, cyl 2 runs 11.5:1, cyl 3 runs 11.5:1, and cyl 4 runs 12.8:1 AFR, when the wideband will just display a seemingly safe AFR of 11.8:1

this is one of the contibuting factors to highly modified LSJs always seeming to blow cyl #4 and none of the others

 

Thanks for the very informative post

 

any time sir.

anyway...i was just curious since the fuel pressures in an LNF are over 2,000PSI...i didnt know if this would make a return style fuel system needed all the more, or if it makes it not needed at all

 

Diesels that run even higher pressure have a return system and other gas systems at normal pressures run return systems. I think the need to run a return system is independant of pressure.

 

returnless. It deadheads at 58psi at the back of the DI pump. THe DI pump is an on-demand volume style that is regulated by a solenoid valve from 700-2200psi.

 

could you explain a little more please? i dont quite understand...

 

It has a valve which only allows in however much fuel it wants. It knows how much fuel it wants by engine parameters and the pressure sensor located on the fuel rail.

 

also

the in-tank fuel pump provides fuel to the engine at the 58psi stated, then the cam driven pump increases the pressure as needed for overcoming combustion pressure. otherwise air would enter the fuel system

 

That's not true, if air enters at 14.4 psi (naturally aspirated DI engine) with a compression ratio of 10:1 it will increase to 144 psi. You don't need 1000+ psi to overcome 144 psi. The reason is for fine atomization of fuel. After combustion when the cylinder pressure rises the injector is shut.