Need help figuring out these new fangled 6.7 a friend of mine at work asked if I could look over his truck he just got an oil change at a jiffy lube and it was running rough after. I drive a older 24v and work on it constantly so I figured they cant be too difficult or different.

Check the engine bay fuel filter first thing and sure as **** no o ring on the fuel filter cap and it was insanely tight. Bought a o ring threw it in ( tightened the bolts that hold the housing to the block was missing a bolt and others were loose) crank the key over to prime and nothing. Do a little googling pull the lid of and look at level and nothing no priming. Checked the lines at the pre filter ( one under the bed) and something is pumping unhooked and verified fuel in and fuel out when key is cycled. Got copious amounts of fuel rained over me. Re installed and still no prime.

I am completely lost. He drove the truck 30 min to work after the oil /filter change but when we fixed the air leak on the filter cap absolutely no prime but the lift pump is pumping? Is their a check valve suck closed or a regulator that is not letting fuel to the filter housing. Any help is appreciated

Sorry forgot to mention truck in question is a 2012 2500 4x4 crew cab that has been deleted

Most likely the in tank fuel pump died. Double check to see if there is 12V power at the fuel sender. If there is power you need a new lift pump (tank sender).

That was my initial thought. Trucks on side of the road so didn't have a tester but cycled the key with the pre filter lines removed and verified in tank pump was pumping. Do these trucks have 2 lift pumps?

Just one in the fuel tank about 300 dollars for a quality pump. One of the few reasons I ditched stock in my 2006.

Even with a new lift pump in my 2006 I was able to pull fuel pressure into a vacuum state. The in tank pumps are low quality and should be replaced with an AirDog (suggested).

Edited June 4Jun 4 by Mopar1973Man

Agree should have been one of the first upgrades to this guy's truck. I'm just trying to get him out of the parking lot for now. Does anyone have a diagram of a common rail fuel system? I cant figure out why I have fuel at the pre filter but nothing at the filter in the engine bay. Thinking their might be a check valve or a regulator thats stuck.

All the check valve and regulator is in the sender.

There are only 4 wires. +5V (gauge), sender GND (not body ground), +12V for pump, GND for pump (body ground)

Like my previous pump made noise but zero pressure.

Hmm it might just be a working pump then but weak and is not able to push fuel all the way to the front fuel filter. Any clue what a healthy pressure or flow rate should be on a stock lift pump?

Should see positive pressure at all times. Say above 5 PSI. Optimal would be no less than 10 PSI at WOT at highway speed.

OK sorry its so late of a reply but we figured it out the pre filters on these trucks has a check valve in it ( for some reason) this particular mopar filter had the check valve too far down in the filter "core" ( when the filter is properly installed a push rod touches the filter body and holds open the check valve) this caused the truck to starve for fuel ( not to mention the air leak at the front filter) i have no clue how this guy made it to work but it explains why we couldn't get a prime afterwards! Thank yall for your help