clhumm

before replacing both batteries, wires and fuel pump, the fuel press gauge would drop from 12psig while waiting to start then to 0psig after starting. the pressure drop would drop with the voltage drop. the voltage drop is from the truck warming up, then the voltage would jump back up. my batteries were shot and the fuel pressure would get to 7psig sometimes while driving so i thought the pump was bad too. as i found out, there is still something wrong. the same scenario is happening with new hardware, start the truck, voltage drops, fuel pressure drops, rpms drop and then voltage goes back up, fuel pressure goes back up and idle increases. could the voltage drain be from an alternator going out? reving up the engine does nothing to the voltage or fuel pressure. thanks in advance for the input.

hummel

kreynolds

I would say the voltage drain is your intake heaters. I think there's a sticky on the subject somewhere around here.

stlhauler

Mine does the same thing, The intake heater cycles--gauge drops-- fuel pressure drops--lights dim. It's normal.

clhumm

thanks for the relpy guys. it has never done this since i bought in '02, it started a couple of months ago. my concern is that the press drops to 0pisg and that the vp44 is going to die.

nickg

fuel pressure dropping to zero is an issue, the voltage drops on start up are normal,
you could disconnect the grid feed from the drv side battery and see if that has any affect on your LP, also any loose battery connections or grounds can cause issues.

get a voltmeter and check voltage at alternator terminal then at the batterys to see if there is any difference, truck shold maintain 13.8 and up to 14.5 at idle (without grids on!)

nickg

do you have a mechanical fuel pressure gauge or electric?

clhumm

mech gauge. had the issue not been happening before changing the batteries, pump and wires i would also suspect grounding issues. i'll check the alt and see whats going on. once the grid heaters are finished cycling, voltage is 14vdc and pressure levels out, a little low at 9psig, but stays constant. thanks for the input.

hummel

nickg

you can also spice into the fuel pump wires and run a light/voltmeter into the cab, this would help tell you if the power to the lp is intermediant or if its the lp its self thats failing

Junk Man

What LP do you have? Grids pull my AirDog to 11#or so, never 0. Grids go off at 20 mph or so. Measured voltage normally doesn't go below 12. (I forgot & don't want to look it up. Info is in FSM.)