So yesterday I put about 300 miles on my truck driving to wilmington, nc and back. On the way there about 100 miles into the trip I noticed my FP dropped down to 5 PSI. Its generally at 13 PSI crusing down the highway. Once I got into town in some stop and go driving FP went back up to normal. Even if I hammered down I could not get it below 10 PSI. On the way back it did the exact same thing. FP was normal until about 100 miles and then it dropped down to 5 PSI. Stayed there for the next 50 miles or so and didnt move. When I started slowing down taking my buddy home it went back to normal. Once the FP got back up to normal I could not make it get below 10 PSI.

Any Ideas? Is it the lift pump or possibly a air buble in the FP gauge line? I have a FASS system sitting in the living room to put on so Im not too worried about it, just curious whats causing it to do this.

 

I would change the fuel filter and see if that helps
if not it probably is the Lift pump and hopefully not
the Injection pump.

 

Both the injection pump and the fuel filter were replaced about 2 months ago. Ill pick up a new fuel filter for it and see if that helps.

The FP gauge line is right infront of the IP.

 

Also possible that it's a bad pressure relief valve at the IP. That valve is supposed to open around 14-15psi, but if it's sticking open, it could be continuously flowing and causing your pressure drop.

 

Mine was doing the same thing, except it would drop to near zero. I replaced it with a FASS system, and haven't seen it below about 17 psi since.

 

mine did the same thing for a week or two and then one day dropped to the 0 peg and would barely come up to 2 @ idle.... I would have never driven it that long, but was told numerous times by the local diesel shop that 5 psi was normal...

Talk about a load of crap! Replaced it with the campaign pump and fp has been great ever since. The old pump was in there for less than 6 weeks when it gave up

 

Wife's truck has done this 3 times. Kept looking for loose connection to the pump or gauge but it was the pump every time. Replaced the pump 4 times in a year. I would really like to know what is happening to them. Every time I changed a pump, it would go back to 13 psi. for about 3 months. I changed the check valve on the injector pump but it made no difference. Original pump ran 108K.

 

I think I would be looking for a problem other then the pump. I'm no expert, but I would be looking at the voltages coming from the ECM, or maybe a short in the wiring somewhere. Just a thought......good luck.

 

So chances are its my lift pump starting to tell me something?

 

After four in one year....I would look elsewhere. My origional last about 120K miles and the second only about 40K. Have you checked all the wiring for shorts, bad connections, etc?

 

That was someone else thats on their 4th. I have only had my truck about 8 months so I am not sure how long it has been in there, but I know it was replaced at some point.