12v Cummins Low Idle Fuel Pressure
 

Ok so I have a 1998 Dodge 2500 12v. When I first installed my Fuel Pressure gauge I was getting 9 psi idle and less than 18 highest. I replaced the OFV with a factory Larry B's replacement. The FP was at 17psi for about 20 minutes then steadily dropped down, 2 days later i was at 11psi idle and would get up to 25 driving. I had replaced the fuel filter, cleaned prescreen, deleted fuel heater, and replaced lift pump. After that I am at 6-7psi at idle and anywhere from 22-30 driving. Now generally after driving a 10 minutes or so when I come to stop it will idle at 15-17 or sometimes 10-12 and sometimes the idle never goes over 7. Whats left to do to fix this? The truck takes quite a bit of cranks to fire up and I get 15mpg no matter so im not sure if its related. Should I buy an adjustable OFV and replace the rubber fuel lines behind the engine? Seems all thats left but Im not sure.
Thanks for any help, the low pressure is driving me insane.

1998 12v, 5 speed, 175k miles, 100 plate, BHAF, 4" exhaust, AFC Tuning.

yes get a ofv

Might want to try stretching the ofv spring on your current one, unless it was faulty a stock one should hold to 25psi. Sounds more like the lift pump isn't making enough pressure. I have a fass so I don't know how much a mechanical should make at idle. Just seems to me that if you have good pressure driving it likely isn't the ofv. Of course you always have the electric upgrade option too, keep us posted!

Ofv regulates the pressure more or less. Stretching it will for sure work but the stock design is garbage and a tork tek one is necessary for these trucks. Plus they are cheap. Def get an adjustable since you have a mechanical lp. Your supposed to have 10 psi for every 1000 rpm you spin. I get the 050 or 060 tork tek for the electric pumps and set the fp at 40-50 psi at idle for truck that spin 4-5000 rpm

I have the Tork Tek adjustable OFV, set at whatever it came out of the box set at. I usually idle in the low 20's with my OEM Cummins LP, and mid to high 20's under load. Coasting down a hill with the lockup switch engaged it's usually 30+. If you want smooth, reliable (well, as reliable as anything electrical) consistent pressure get a FASS or Airdog. I don't know what you're problem is, but I'm curious about your pressure gauge setup. Getting a gauge to read FP with a mechanical pump is a trick, and there's a little bit of magic to the science of doing it right. Which is to say, I'm not saying your readings are wrong, I'm just not saying I completely believe they're right either.

Larry B's ofv non adjustable. The set up is a tork tek snubber 14mm or whatever threads right into the injection pump, then 3 feet of hose and my sensor. Very minimal to no needle bounce.
Currently getting 4psi at idle.
I dont want to go to an electric setup if my issue is an air leak somewhere as theres a chance itll be there after spending money on a fass. Just got back from a camping trip, going to check all my hoses and go from there at this point.

Ive also had an issue with my fuel gauge dropping to empty below 3/4 tank but it works again below 1/4 tank. Possible issue from the tank area?

Not sure how those two issues could be related, but can't say they aren't either. Generally that suggests a worn spot on the float reader, and a new float is the only solution. I really can't see what it would have to do with your fuel pressure though, unless it's somehow not working right because it's loose in the tank which is also creating an air leak, but I've never heard of this with one of these trucks. Gauge setup seems sound. Your OFV could be defective, or as you said, there could be an air leak somewhere. Do you still have the old OFV? Might want to put it back in and see if pressure goes back up to idling at 9psi again.

Ya I dont think theyre related either but you never know. And ill swap in the old one and see what that does, never thought of tryin that thank you.

Well, I haven't found the OFV to be the Heavenly Messiah that some have. So there's a chance that it will make no difference in your pressure at all. But if it does, then you'll have a suspect. A frustrating suspect, because nobody likes to take defective parts out of a new box, but any lead is a good lead, yes?

Ok so intalled the old ofv and it stays around 7-9 psi all the way up to 2k rpms. The new ofv will immediately climb up to around 30 psi as i rev it up. So my Larry B ofv is good? So air leak im guessing.