PaulDaisy

Does anybody know how much fuel does a good stock lift pump put through the fuel system at idle and at WOT? Maybe somebody measured the volume of fuel from the tank return line?
Thank you!
-P

PaulDaisy

Well... can someone see if my logic is faulty:
At cruise speed, 2000 rpm, my truck makes 70 mph and uses 18 (edit: MPG) (hand calculated).
This amounts to 3.9 gal / 70 miles, or 3.9 gal / hour. Right?
The FSM says that over 70% of fuel is bypassed at the injection pump, so this means that the total flow, including the return, is:
3.9 / 30 * 100 = 13 gal/h
Does this make sense?
-P

george7941

There is some kind of typo in your calcualtions, you went from 18g/hr to 3.6g/hr. DC has a value for free flow from the pump,I don't remember the figure. I don't know if anybody has measured the fuel flow thru the return line.

Truckman

http://dodgeram.info/tsb/2003/14-002-03.htm

PaulDaisy

Oops, I meant to say 18 miles / gal. Then I got 3.9 gal/hr. Sorry...
Truckman, thanks! From this, looks like free flow is about 50 gal/hr. If I only could find the pressure curves for the Carter pump, it would tell me what the load flow is.
-P

bent valves

The VP44 on my 5 speed, 1998 ETC engine in stock form burns 0.393 lb/BHP-HR at 3200 RPM (TDR issue 29, pp 48) and is making 225 BHP. Multiplying 0.393 x 225 = 88.43 lb/HR of fuel burned. Diesel at 7 lbs / gallon, is 12.63 gallons per hour when making this BHP. The fuel flow back to the tank is about 30 gph for a total of 42.63 gallons per hour required from the lift pump. The Carter lift pump delivers 60 gallons per hour at 8.5 psi and 40 gallons per hour at 12 psi. These numbers are what I have measured from a good lift pump. Someone wrote, years ago, that the filter assembly will only flow about 45 gph with a 5 psi drop in pressure, enough for a stock engine but not enough if you bomb. To get around this limitation with the filter you need to raise the fuel pressure.
I have been collecting this info since 1998 because of the problems with the VP44.

PaulDaisy

bent_valves - Thank you Sir, this is pretty much what I was looking for! Although certainly the 12.6 gph is not the consumption I see on mine, this is more like 5 miles per gallon at 70 mph. Looks like the rated consumption per horse power is only developed on a dyno, on the road the engine never develops the full rated HP unless towing very, very heavy.
Thank again!
-P