New lift pump, Confused!!!?

[Jetpilot]

Here is some fuel for the fire... Have you guys looked at the size of the fuel line from the OEM fuel filter to the VP44? It is VERY small in diameter! So a reading at the base of the fuel filter as opposed the the inlet of the VP44 could very well be different. If the line is so restrictive as to not allow enough fuel to flow even under proper pressure at the lines inlet then there would be a loss of pressure closer to the pump.



Personally I think that if the gauge is not erratic and it drops smoothly with application of throttle then the VP44 is not affecting the reading. I for one want my gauge to get its input from a source as close to the component I am concerned about (for me the VP44). Some of the guys have had erratic gauge indications when the sending unit is attached to the schrader valve at the VP44, but again if the gauge seems to operate smoothly I would suspect the line restriction.



This is just my $. 02 worth



Doug

 

[Bob Cochran]

Jetpilot~HHMm not sure I know what I am talking about but would not a small line make fuel flow higher or lower like gallons per minute or something. I don't think line size will change PSI. I know electrical a lot more than fluid mechanics. Sure someone here will straighten us both out if necessary!!!

 

[Jetpilot]

If the fuel is pressurized say to 15 psi at the OEM filter (using the stock 3/8 line) but the the line from the OEM fuel filter is alot smaller than 3/8 then it is possible for the VP44 to require more fuel than can be pushed through the line with a head pressure of 15psi. That is why alot of guys are switching out the OEM fuel lines for larger ones... .



I see what you are saying about pressures going up but that would assume forcing the same amount of fuel that can go through the 3/8 line down the smaller line. Does this make any sense or am I being clear as mud?



Doug

 

[RADdodge]

Jetpilot

I have to confess that I haven't looked at the line size from the fuel filter to the injection pump. I hate to say it, but I assumed the line was 3/8 inch throughout (you all know what assume means!). I have an SPA gauge mounted on a modified aluminum bracket that replaces the stock bracket mounted to the master brake cylinder booster (I already posted a picture of that somewhere, don't want to bore you with picture details). I'm using a snubber hose (grease gun hose) to absorb the hydraulic impulses from the injection pump that I've read about here. Pump pressure on the gauge is steady. However, if the line is a different size, then there would be a difference between mounting the sender at the injection pump inlet (where I have it) compared to the outlet of the fuel filter. I will look at that real hard with a view to replacing it ASAP (along with adding a check valve to bypass a failed lift pump). Thanks for the heads up. I missed that.