fuel return line?

[Mikey90744]

well, I'm only starting this new thread cause I don't want to hijack Heavysteven, which I should have done in the first place, in( http://www.steelsoldiers.com/deuce/71044-oil-leak-exhaust.html ) Heavysteven replaced his fuel return lines from the top of the injector, when I asked what it was for, he answered exactly what I assumed it was for, how ever my question is with a return line from the injectors that's bleeding off excess fuel, wouldn't that effect performance since a diesel is throttled by the amount of fuel squirted into the cylinder and that is regulated by the injector pump.

or does it have to do with the pop off (think thats the correct term) pressure and bleeding down the say 100 PSI left in the line that it takes to activate the injectors????

I do have a pretty good knowledge of how a diesel engine works, but for me personally its only been applied to modern electronic diesels

 

[Bill W]

As I was once told ( second hand info )
( Older ) mechanical Injectors have to be cooled ( around 160° ) and that is what the excess fuel is designed into the system to do

 

[Mikey90744]

As I was once told ( second hand info )
( Older ) mechanical Injectors have to be cooled ( around 160° ) and that is what the excess fuel is designed into the system to do

I could see that, not sure why since you need the heat to burn the fuel, but Im still LOST. what do the injector always return say 25% of the fuel to the tank? or is it pressure depended? thats whats baffling me

 

[kennys@wi.rr.com]

After working on one of these when my HH went out, from what I read the injectors will not open until the fuel preasure reaches 2200 psi. The return line is for the fuel that just didn't make it. The preasure in that return line is minimal at best, maybe a few psi but no where near 100. The main thing you will always hear is stay away from the injector lines if they are not connected because it can actually force fuel into your body through the skin and that is very bad. But the return can almost be stopped with your finger. As always I'm sure there is someone with way more knowledge than me that will have all the charts and facts to prove me wrong, I just know what I have experienced.

 

[m-35tom]

as the fuel pressure is applied under a small plunger with a needle valve on the bottom end and a very strong spring on the top, the pressure lifts the plunger and fuel is injected. at the same time because of the close tolerances a very small amount of fuel passes by the plunger and gets on the top side of it. if this fuel did not have some place to go (return line) it would fill the spring area and the plunger would have no place to move as the fuel could not be compressed.

tom

 

[kennys@wi.rr.com]

Very helpful information Tom.

 

[Mikey90744]

as the fuel pressure is applied under a small plunger with a needle valve on the bottom end and a very strong spring on the top, the pressure lifts the plunger and fuel is injected. at the same time because of the close tolerances a very small amount of fuel passes by the plunger and gets on the top side of it. if this fuel did not have some place to go (return line) it would fill the spring area and the plunger would have no place to move as the fuel could not be compressed.

tom

well thank you gentlemen I figured it was something so simple that Im to stupid to figure it out, I was right.

Thank you M-35tom and kennys@wi.rr.com

 

[m-35tom]

new injectors or those in very good condition would probably have almost no fuel at the return line while worn injectors might have more. basicly there would be a very limited amout of fuel in the return and there should be almost no pressure as it should just flow back to the tank unimpeded.

tom

 

[Bill W]

I could see that, not sure why since you need the heat to burn the fuel, but Im still LOST. what do the injector always return say 25% of the fuel to the tank? or is it pressure depended? thats whats baffling me

I know a Detriot diesel returns 70% of what gets pumped up to the injector back to the tank. It was several marine diesel mechanics that told me about the cooling of the injectors with excess fuel I just don't know if it was only particular to the detroits. Heat comes into play during compression not on injection. I know newer injection system on marine engines deadhead at the injector ( no return ) and with pressures up to 10,000 psi, for saftey sake the injector lines on these engines are double walled

 

[Katahdin]

The return line sure does send a lot of fuel back to the tank. I learned this when bleeding the secondary filters/lines after removing and overhauling the fuel tank. After I killed the accessory switch, and thus the low-air buzzer, I heard what sounded like the soothing sound of a tricking waterfall.... The numb-nut posting this forgot to reattach the return line.

At least I knew in the in-tank fuel pump was re-hooked up correctly!

 

[DMaddox]

just yesterday in was changing fuel filters and bleeding the system, and heard exactly the same sound you just described, and now I understand the sound I heard... Great Thread.! simple and informative..

 

[m-35tom]

a detroit has an entirely different fuel system and cannot be compared in any way to the one on a deuce. comparing the flow from the injectors, to the return at the tank is also completely inaccurate. the flow at the tank includes the cooling flow from the HH. remove the 1/4" line from the injector return at the HH return metering valve, plug the connection to the valve and you will be left with the return from 6 injectors. i think you will find it is VERY small.

tom