2001 2500 fuel pressure problem

[jeff77indy]

I've been having a problem with the transfer pump pressure on my '01. Since installing the Walbro GSL392 kit from Glacier Diesel about 14 years ago I've had 18-20 pound pressure at the inlet of the VP44. about a month ago I noticed the pressure was at 12 pounds, but would go back to the 18-20 pounds at times, so I changed both fuel filters with no change, then changed the transfer pump with a new Walbro GSL392 with no change. I've cleaned the pressure by pass check valve and also replaced it, still the same. I get the same pressure on two gauges.
I am getting these codes using the ignition switch procedure P0123 and P1693. I get no codes with my scanner. The transfer pump has 13.2 VDC at the terminals.
The transfer pump does not always start when the ignition switch is turned to the on position, but will start if the the starter is bumped.
Would the bypass valve in the VP44 be bad and causing the loss of feed pressure?

Thanks
Jeff

 

[KATOOM]

The P0123 code is referring to the APPS and the P1693 is a companion code telling you that there "could" be another issue going on. When things like this happen its a good idea to start looking at battery condition, alternator AC voltage levels, battery cable condition, all major connections/cables/grounds for tightness and corrosion. These trucks are very sensitive to electronic anomalies caused by those items mentioned.

As for the fuel pressure, are you positive that the gauge or sender is telling the truth?

 

[jeff77indy]

I'll check all the battery and ground connections. I had already tried a new control relay for the transfer pump.
The pressure was taken with both my dash mounted mechanical gauge and a mechanical test gauge, both taken at the inlet of the VP44. The test gauge takes all the plumbing for the dash mounted gauge out of the equation.
What should the voltage at the transfer pump be?
I have dropped the fuel tank and checked the draw straw and fuel tank cartridge for possible blockage of the screen in the bottom of the cartridge. Good thing I did as the brake line to the rear axle was in pretty poor condition.

 

[KATOOM]

Voltage to the lift pump should be at least 12 volts, except during engine cranking whereby the voltage is cycled on/off in order to reduce fuel pressure at that time.

 

[Joe Mc]

I have same system for about same length of years and ran into similar problem it turned out being a loose crimp connector at the pump. I purchased solder-able terminals and installed new wiring (just to eliminate the potential variable) and its been good since, probably 3 years or more.

I'd be driving down the road and psi would be fine then I'd notice a fluctuation and sometimes 0-psi. An intermittent problem, but didn't like it at all.