I'm working on my VP44 and ECM projects and need to know how much fuel is actually injected by the injection pump.

This is so I can calculate a fuel rate in milli Liters for determining engine load and also for the overhead trip, mileage display 

computer. So i dug out my old VP44 core and did some measurements. I thought I would share what I found and get some

confirmation or feedback. 

 

This is a SO pump with three injection plungers they are 7.3 mm diameter. The cam donut has a thickness of 10.5 mm at the maximum inward

point and a thickness of 7.1 mm at the maximum outward point. So 10.5 - 7.1 = 3.4 mm of stroke. I don't have an ultra precise way to

measure the stroke. I probably need to have the pump all put together for that with a special instrument and rotor head fixture, but it's 

probably pretty close. So 7.3 divide by 2 = 3.65 mm radius times 3.14 (pi) times 3.4 stroke = volume  39 milli liter per plunger, times 3 =  117 ml.

That's the theoretical maximum injection volume without injector or line losses. So 3 injections per crankshaft revolution is 351 ml. times 1000 RPM

is 351000 ml. There are 1,000,000 ml in a liter so 0.351 liters per minute at 1000 RPM. At 2849 RPM that's 1 liter / minute.

 

The vane pump has to fill the plungers and it continues pumping to the tank while the plungers are injecting so that means it needs to

pump at least twice the amount as injected. That needs 0.702 liters / minute @ 1000 RPM and 2.8 liters @ 4000 RPM.

1 liter is 0.264 gallon so 0.74 gallons per minute @ 4000 RPM. that's 44.5 gallons per hour. The lift pump would need to be 2 to 3 times that to maintain a good working pressure at the VP. Does the math seem right?

 

 

1 hour ago, Great work! said:

There are 1,000,000 ml in a liter

 

I believe that there are 1,000 mil in a liter.

 

Does this help?

 

 

 

I think you can get pretty accurate with the high pressure side of the injection pump, but not so much with the vane pump.  Even though the vane pump is fixed displacement, I have never been able to find documentation of volume displaced per one revolution of pump.  To further complicate matters, is that the vane pump puts more fuel over the regulating valve at higher rpms that it does at lower rpms - in fact, at low rpms the vane pump may not even put any fuel over the regulating valve - nobody seems to know.

 

I performed return fuel flow tests that showed 19 gph at idle and 28 gph at 2,000 rpm.  So, theoretically the the fuel return volume should have more than doubled at 2,000 rpm, but it didn't.  So, being that the vane pump is fixed displacement, this would mean that there is lots of fuel passing over the regulating valve when the engine is at 2,000 rpm.  How much, who knows? 

 

Below are some fuel return flow tests I performed from the VP44 to the fuel tank.  The VP44 is an HO pump.

 

For the tests I used a one-gallon oil jug with volume markings at one-quart intervals.  I used a helper and started the clock on the 1 quart mark on the jug and stopped the clock on the 3 quart mark on the jug.  The total volume returned for each test was .5 gallons of fuel.

 

My truck is a 2002 2500 with a NV5600 transmission.  The fuel lines are stock diameter, the fuel filter is the OEM filter inside the filter housing mounted on the engine, and the lift pump is a used frame mounted FASS DRP-02 that probably flows somewhere around 65 GPH - 12 psi @ idle and about 6 psi @ 2,000 rpm.

 

I performed the tests as follows:

 

Test #1:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 92 seconds

Test #2:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 94 seconds

 

Average fuel pumped is .5 gallons in 93 seconds = .3225 gpm rounded to .32 gpm or 19.35 gph

 

Test #3:  engine at idle, fuel transfer pump disabled and bypassed   - .5 gallons pumped in 93 seconds

Test #4:  engine at idle, fuel transfer pump disabled and bypassed  - .5 gallons pumped in 95 seconds

 

Average fuel pumped is .5 gallons in 94 seconds = .3191 gpm rounded to .32 gpm or 19.35 gph

 

Test #5:  engine at 2000 rpm, fuel transfer pump disabled and bypassed  - .5 gallons pumped in 64 seconds

 

Fuel  pumped is .5 gallons in 64 seconds = .47 gpm or 28.1 gph

 

Return flow tests were done by a couple of guys on the Turbo Diesel Register in April of 2001.  There test results were very close to mine.

 

 

- John

 

 

 

Edited November 20, 2024Nov 20 by Tractorman

Thank you @Tractorman that's just what I needed. That other spec of 1.9 m/sec at 1000r/min is interesting.  That may help define the slope of ramp area on the cam donut.

37 minutes ago, Great work! said:

That other spec of 1.9 m/sec at 1000r/min is interesting.

 

I was thinking that you might find that specific information useful.

 

- John

Have you considered using a volumetric sensor? They sell for about 60 bucks for metering fuel on farms. You could pretty easily set the fuel to specific values and see what the flow in is, then measure the return out flow, subtract them and get a real measured result. I'd be super curious what the results where

I might have to try that. I would need to keep a steady load on it for a few minutes to get any accuracy.