Will a failing VP44 draw more voltage under load? I discovered last Tuesday that one of my batteries had failed, so I replaced both with 2 brand new batteries. After installing the  batteries, the truck starts hard when cold or sitting for 8 hours or more, and runs incredibly rich. This morning I noticed my fuel pressure drop from 18psi to 16psi, and on my way home the pressure would drop from 15psi at idle to 5 under load then come back up to 13ish. FASS said to check my VP44 overflow valve, that it sounds like its returning more fuel than using. I'm assuming the pumps original to the truck and has 160k  on it, could it be seals are worn out and leaking fuel past causing the rich starts? I also noticed today that at idle the injector pump just didn't sound the same, I haven't witnessed any dead petal issues but I do see weird rpm fluctuations (less than 100 rpm) under acceleration. Any ideas or suggestions would be greatly appreciated.

 

 

 Alright I did some voltage testing and talked to a few people, and it looks as if my alternator is bad. With the truck  off the drivers side battery reads 12.5V and the passenger side reads 7.5V. At idle the drivers side reads 14.5V and the passenger side reads 7.5V. I'm assuming that both batteries were fully charged when installed, and over the course of 5 days the passenger side battery slowly discharged to the point that  its creating my voltage issue. I figured I had about 2.5 hours of run time in those 5 days.

 

 My issue with the hard starts I think can be narrowed down to the grid heater not working.

Edited April 6, 201510 yr by 440Rat

Was the passenger side battery the one that originally failed?

That I don't know, I tested the voltage at the FASS pump  by jumping the relay, before swapping the batteries. Not running it would read 12V and at idle it read 3.8-.01 volts. When I tested the battery at idle the drivers side read 14.5 and the passenger side read 10.5. With the truck shut off for a few minutes i checked both batteries and they seemed to be equalizing each other in voltage. When I swapped the passenger side battery with the drivers side, and jumped the pump relay it ran and built pressure like normal. I couldnt test the voltage at idle because when I went to start the truck something went "pop" and I had no power to start the truck.

 

 With 2 new batteries everything worked fine for 4 days minus the grid heater which I figured out today wasn't cycling. I charged up the passenger side battery tonight and the Fass pump runs like a dream,  but that battery isn't charging while the truck is running. What I cant figure out is why the dash gauge reads 14.5V and the drivers side battery reads 14.5V at idle but the passenger side battery wont charge. Its obliviously discharging that battery but wont charge it, if its not charging why would it read that it is on a gauge? Could the wire that ties the positives together be bad?

Sounds like your main battery cables are bad if the voltage is not the same.

 

As for the VP44 is only turned on if the ECM commands it through the fuel pump relay. So the VP44 can draw while thee key is off. Also if the battery cable where good the batteries should be matching at all times. But your batteries are different voltages running or not. So that points to bad cables.

I agree with checking the cables. Either you have some serious corrosion issues going on, or you have a bad/no connection between the batteries and/or grounds. Get them checked quick. If all the connections are good, both batteries will be the same voltage. The other thing I might do, load test each battery on its own (disconnected completely from truck). This will just make sure both batteries are in good shape. I have had more than one brand new battery that would not come close to passing a load test right out of the box.

I replaced the cross over cable, drivers side positive and negative cables with 3/0 wire, along with the 2 grounds on the drivers side with 4 ga. wire. Both batteries charge evenly now and everything seems to be working just fine.