Engine/Transmission (1998.5 - 2002) What is the fuel flow in a 3/8" line?

[J.R. Adkins]

No i understand that is what you use it for! Yes the vp44 can only supply so much fuel! Its time for a P-PUMP! I have one that puts out a a** load of fuel ... ... but its in use! We just want BIGGER chargers!! Im drug free and likeing it!!





J. R.

 

[15w40]

Diesel Freak, to answer your question, the spillback valve in the lift pump will open at 15 psi. This number may be 1 or 2 psi different on different pumps. And as the spillback spring fatigues, the pressure will drop from the starting 15 psi and become erratic.



As far as bigger injectors having no effect on fuel pressure from the lift pump, I can not agree. The bigger injectors use more fuel by injecting the charge sooner and longer in the VP44. Picture it this way, the piston in the VP44 pushing the fuel charge through a stock injector creates about 17000 psi as the fuel is forced through the small orifices. This causes the steel fuel lines to expand and the VP44 piston and bore and drive rotor to deflect under the load. This deflection reduces the amount of fuel injected. Using large injectors reduces the maximum pressure greatly. The pop off pressure may still be the same but the max pressure is a lot lower. The swash plate inside the VP44 is now working under a lot less pressure and the components see less distortion, and more fuel is injected.



Using large injectors, the lift pump must provide more fuel because the VP44 is trying the keep the pump body at about 15 psi. less fuel is returned to the vane pump inside the VP44 and more is required from the lift pump.

 

[Diesel Freak]

well, I think we are going to have to agree to disagree on this.



if the fuel lines and pump rotor assembly are distorting the way you are saying they are, then the stresses will cause fatigue and eventual failure. I understand that they will deflect within their elastic limit, and they are engineered not to exceed the elastic limit on the components, but their is no way in HE double hocky sticks that the ammount of deflection you are talking about will allow more fuel to be pumped by the VP44. If the distortion is actually measurable, then the pump would fail.



It is capable of producing up to 21000 PSI.



but if you fo have the equipment to attach a strain gauge to the injector lines and the pump rotor assy them please tell me the ammount of deflection of the material... then compare it to the elastic limit of the material.



Sorry, and dont take it personaly, but I have to emphaticly disagree!