Finding & Fixing your air leak.
So you found out that you have an air leak somewhere. In this article we’ll find it.
In addition to this article, this is also a good read. Joe G's Fuel System Write-up
The air leak can be anywhere from inside the fuel tank, to the lift pump.
Finding the Air Leak
If the leak is large enough, it may drip when the engine is not running. If you are not that lucky, you may have to persuade it to drip by taking an air compressor and pressurizing the fuel tank to 10 psi MAX. to pressurize the tank, take an air nozzle, wrap a rag around it, and insert the contraption into the tank fill-up spout. Now just watch for leaks! If no leaks are found, the issue may be in the fuel tank. Also, if the lift pump primer is leaking fuel, it will likely leak a little air as well.
The fuel lines in the fuel module in the fuel tank can wear holes and suck air.
You will need to replace the lines in the tank, LarryB’s has a good kit. Or you can install a Draw Straw or Sump.
Fuel Quick Connects at the tank.
They are called “quick connects”, but really they are the least quick connect fittings imaginable, especially at the odd angles you will be forced to be in in order to even see it. The quick connect has an O-ring it in that can have a flat spot in them.
Replaced the quick-connect (3/8” Feed, 5/16” Return), or as many owners have done, replaced the rubber hose (3/8” Feed , 5/16” Return) that the quick connect is on, and just slide the hose over the male portion of the quick connect on the fuel module. This method has been used many times, and I have yet to hear of any failures.
Fuel Lines along the Frame
If your truck is somewhat of a rust bucket, the fuel lines are going to be one of the first things to go.
You will need to replace the lines, there is a large array of replacment options, including stainless steel lines, and the more popular and DIY friendly, Rubber hose option. If you use rubber hose, make sure it is Diesel Rated. Marine Grade would be recommended. Trident A-15 Marine Fuel Line is good stuff, at an affordable price. LarryB’s also has good kit. When re-doing the fuel system, if you bypass the pre-screen (I wouldn’t), make sure to use some form of screen before the lift pump. Avoid too much restriction as the lift pump doesn’t like having to pull through to fine of a filter.
Fitting sizes are as follows: Lift pump inlet – ½” BSPT (NPT work fine), Pre-filter inlet/outlet – 3/8” NPT.
Fuel Heater/Pre-screen unit
The fuel heater is well known for its likability. The rest of the prescreen unit is very reliable.
Delete the pre-heater.
Pre-Filter to Lift Pump Hose.
It is common for this hose to leak air, it may look good on the outside, but the connections can leak air.
The cheapest place to get a new ones, surprisingly, is the Dodge dealer, Cummins Dealer is much more expensive. Or you can get one from here http://www.genosgarage.com/product/mop-04746638/hoses
The Inlet Fitting may leak, along with the primer seal.
If the issue is the primer seal, some of the old pumps has a normal O-ring that sealed it off. If your is like that you can try replacing the O-ring. Otherwise if your pump in not like that, then you need to replace the Lift Pump. http://www.genosgarage.com/product/pump-4988747-kit/fuel-pumps