Engine/Transmission (1998.5 - 2002) What EXACTELY is the injector return line?, et al

[rweis]

We have a VP44 return line and an injector return line that meet at a T at the rear of the engine.



Why was the injector return line designed to do what? How does it do what it does do? Are all the injectors tied together?, if so how?



How hot would you think the return fuel is? Head temperature?, water jacket temperature?, some other temperature? 100°, 200°, 500°, 1000°



There was a old thread of "pumps, lines, and whatnots" that talked about the volume of return fuel. The return fuel is VP44 return and injector return. Approximately how much of each? 90%/10%?, 60%/40%? ideas?



Trying to figuer out exactely what is contributing what to the return fuel.



Bob Weis

 

[Gary - K7GLD]

Strange - I just tried a search on that "Pumps lines and whatnot" thread, and the system couldn't find it, or ANYTHING past about 7 pages worth of listings. I wonder what gives?



I've always been able to bring it up before...

 

[R-N-R]

Awesome Thread!!! pumps, lines & whatnot



I had it saved in my email

 

[RJPotts]

To answer your question, the VP44 only pumps about 35%-40% of the fuel it receives to the injectors, therefor 60% is used for cooling, lubrication, etc... and returns to the tank.

Also, not all of the fuel that goes to the injectors is injected into the cylinder. Some of the fuel that passes by the needle valve when the "needle" is unseated does not exit the orifii, it is under such a pressure that some of it sneaks up the barrel and into the top of the injector. It has to have a place to go or the injectors would hydraulically lock so there is a return line.

As for a ratio of fuel from the pump as compared to the injectors. It should be a VERY small amount from the injectors unless you have a worn out injector. But even in that case, it should still be minimal in comparison.

For an, off the top of my head percentage of fuel from the injection pump and injectors (considering all injectors are "good") 99% and 1% respectively.

-R. J.

 

[Gary - K7GLD]

I think one of the things Bob is asking is what PATH the injector fuel return uses for the return trip to the tank - part is OUTSIDE the engine, T'ing into the same line from the VP-44, then on to the tank - but PART of the return path SEEMS to be a gallery inside the head? Is that correct?



And if so, how much heat does the returned unused injector flow pick up from the injectors/head?

 

[Gary - K7GLD]

Awesome Thread!!! pumps, lines & whatnot



I had it saved in my email

Good idea, I refer to that thread from time to time, so just saved it to My Documents... .

 

[Bob4x4]

I think one of the things Bob is asking is what PATH the injector fuel return uses for the return trip to the tank - part is OUTSIDE the engine, T'ing into the same line from the VP-44, then on to the tank - but PART of the return path SEEMS to be a gallery inside the head? Is that correct?



And if so, how much heat does the returned unused injector flow pick up from the injectors/head?

Yes the head is rifle drilled for the injector return. If you are curious about the temp just shoot that line during a dyno run.



Bob

 

[Todd T]

Yes the head is rifle drilled for the injector return. If you are curious about the temp just shoot that line during a dyno run.



Bob

to sum the two up, the injectors dont discharge all the fuel charge into the cumbustion chamber, like the VP the injectors are lubed with fuel as well. this miniscule amount of fuel backs out the injector around the fuel tube and is carried off through a common passageway in the head where it exits and T's into the return from the VP to the tank.



I'll have my head off this week. while i have it out I'll try to shoot some pics of this.

 

[rweis]

Pics of the passageways and how they work would be great! It would help explain exactely how this happens.



Bob Weis