Had to let truck set for two months during cold weather. Now takes several seconds to start. Even after on prime will not start quickly. Checked LP pressure of 12 during prime run and 8 while idling. Replaced banjo return fitting (pres reg) with same results. LP and VP44 have 25,000 miles and 14 months old with no fault codes. Sometimes get started quickly if catch during prime run. If pump shuts off and then crank is slow starting (3+ seconds) for first time. Will restart immediatelly for up to one hour and then the slow start comes back. Guess I'm looking for a vacuum leak. Any thoughts?

 

Sounds like LP is going , it should be higher pressure at idle 12-15 psi. , and lower at WOT , 7-8 psi.

 

Make sure your lines are good esp behind the tank on the frame rail. A leaking return line can also cause issues.

 

Follow up. After two lift pumps and inspecting hoses in engine compartment cannot keep prime. Made jumper wires to run lp continious. Will have no pressure. Open water drain valve. A little fuel drains then pump catches fuel and gushes out drainhose. Shut valve off and pressure to IP is 16 psi or so. Shut power for one second and lose prime. Repeat bleed and pressure returns. Run for 5 minutes and same results.
Engine will not fire up till lp pressure hits 10 psi, or 4-5 seconds on first start. Will refire immediatelly on crank for at least 10 minutes. Wait 1 hour and 4-5 second start returns at first crank. Once started, engine runs like always and does not miss a beat as if had any air in IP.
With lift pump running, have loosen filter cover and allowed air to be forced out around threads. This helps but returns again.
Guess ready to pull bed in inspect hoses and module assy. Other thoughts?

 

There/s a check valve in the banjo on the return line of the injection pump. It is just forward of the input line. If it is not sealing shut, it will allow air to back up into the pump and so on. They are fairly inexpensive to replace..
Part number is 3941156

Here's a quick test. Get a set of vice grips adjusted just so they will pinch the rubber fuel line just before the vp. Get the truck started and let it run a bit. Now shut it off and pinch that line shut. Wait however long it takes to lose prime, remove the clamps and see if it fires. If it does, then that check valve is probably bad..

 

Maybe try the overflow vlv in the injector pump. It's in the banjo just beside the pressure test port on the VP. It restricts fuel returning to the tank and is supposed to open at 14 psi.

 

The banjo fitting you speak of has small constant bleed orfice and a 14 psi (+/-) release ball and spring. Three of them test the same and did not fix unit. I am sort of on the track of eliminating any air captured in top of filter housing. It appears fuel is pumped into side of housing near top and exits from a port at bottom fed by a vertical pipe in filter. Air could be captured in that upper area on the outside of the filter and never purged.

 

Yeh sorry I see in your ORIGINAL post that you have already replaced the overflow vlv. If this is not the problem and you have NO fuel leaking on the ground then it must be a leak in the non pressurized section from the tank to the pump.

 

I had my bango fitting loose on the injector pump. I was fine for four year I had the truck, then one day it started starting hard and a 24 hour sit time. The bolt wasnt' even leaking anything but was loose enough to let air back into the system.

Dan