Just replaced lift pump and filter about 3 weeks ago. Overall pressure was about 1 psi lower than before.
14 idle
12-13 cruising
10-11 WOT

Now the pressure will drop down to 5 while cruising. I can really punch the skinny pedal and the pressure will jump back to above readings and then look back at the gauges and its back down to 5

Just pulled the filter and the fuel from the canister, both appear to be clean. What else can I do?? It seems to have something clogged up in the lines. Thanks!!!!

 

With the filter and canister off could I place a small bucket in place of the canister and cycle the lift pump (without trying to start it) to try and empty out the fuel lines comming from the tank and possibly any trash that might be in the lines????? Just a thought.

 

I just had a bad LP out of the box also. It's the LP. I replaced it with a FASS II.

If you bought the pump from Cummins they carry a one year warranty.

 

I bought a 1/8 NPT X 1/4" hose barb fitting and a lenght of 1/4" tubing to test the volume flow. Mine was right at min for the pump, 45 OZ in 25 seconds. If you bump the starter (don't start it) the LP should run for 25 seconds and stop.

I took mine back after I installed the FASS II and got a refund. You could just get another one for now.

 

I got it from O'Rilley and it was under warranty. This one is still under that same warranty so I guess we will try another. Also the seals on top of the filter seem stretched and to big now... could this be a problem. The new washers/o-rings were replaced with the new filter about 3 weeks ago.

 

mine did the same thing. Check your fuel supply line from the tank. Mine was sucking air.
Bob H

 

I think they get stretched if you use the nut to tighten the filter in place. Next time try a little grease on the o ring and fit it in place by hand.

 

You also may want to look at the power supply to the pump. Is the wire still conducting the full amount of juice. I was having the same problem and went with a new relay system advertised on Product Engineering websight that is 2 30Amp relay run together right off the starter lug for extra juice. This is my second relay system, but this one is far and above the last one in quality.

 

Do I check this line at the tank or the LP? How did you fix it... just tighten it? I wanted to disconnect the fuel line from tank and LP and use a compressor to blow air out of lines but I can not get to the lines at the tank (without raising bed or lowering tank!)

 

On the frame rail, right under the drivers seat, there is a slip connection. All it is, is the rubber fuel line slid over the steel line from the tank. Mine was almost off. Every time you move the banjo fittings to work on the transfer pump, you have a tendecy to loosen it a little. Two 89 cent hose clamps fixed the problem 9K ago, and I still have a brand new pump in the tool box.

 

Do yourself a favor and use a clamp like this designed for fuel injection lines instead of the old Worm style clamps.
They will do less damage to the hose and give more even pressure.

 

I just got home from work and will try that before I go back to work. I have seen the place you are talking about so I sure hope this is a fix. I have decided to sell this truck and get a 4WD so I am trying to make sure eveything is working properly first. Thanks again for all the help I will post results soon!!!

 

Well I put on clamps and rechecked all fittings from clamps to LP banjo bolts including all fittings that fuel runs through (all gauge fittings) and everything seems tight. Went for a test drive and pressure still drops. Not as bad or low but still drops to 7 or 8. The search continues...............

 

Since it seems I have checked everything else how hard is it to drop the fuel tank, and what are the chances I will find the culprit there? I still believe it is sucking air somewhere but can not seem to track it down ! This may be the last resort......... now if the insurance co. could just find the guy who set my truck on fire

 

It isn't that hard to drop the tank. I did it last summer because I changed my fuel gauge sensor. Just two bolts and it's loose.