Fuel is drawn from the tank by a lift pump (figure 5-12) mounted on the inside of the left frame rail. The lift pump pressurizes the fuel at a rate of approximately .24 liter (1/2 pint) in 15 seconds (15 GPH). Pressurization rates are as follows:
• On model year 1988-1993 pumps (p/n 25115224), fuel is pressurized to between 40 and 60 kPa (5.8 to 8.7 psi, tee in running at idle)
• On model year 1994 and later pumps (p/n 25117340), fuel is pressurized to a 3 psi minimum with the line open (after the filter) to an approved canister and the engine cranking.
From the lift pump, fuel is carried to the transfer pump. The vane-type transfer pump varies the pressure of the fuel, depending on the speed of the engine. At idle, the transfer pump outlet pressure is approximately 20 to 30 psi. At full engine speed, the transfer pump outlet pressure may be over 100 psi, with a maximum of 125 psi.
A regulator valve controls transfer pump outlet pressure. The valve uses a viscosity-compensating orifice. This regulator valve is at the end of the hydraulic circuit, rather than directly at the transfer pump. As with other previous 6.5L diesel regulators, however, it spills fuel back to the transfer pump inlet.
