Engine losing prime

[Awesomeness]

When I first start my engine, it generally starts within a few revolutions, runs for ~5 seconds, then dies. It then requires ~20 seconds of cranking before it will start back up, after which it will run fine.

To me, this sounds like initially it's starting using whatever fuel is in the lines/passages close to the engine (e.g. in the injectors already), but once it consumes that there isn't more and stalls. That would mean the actual fuel lines from the tank, to the water separator, and to the engine, are empty. Once you crank some more, it draws fresh fuel into those lines and can run again.

Sound about right? Where to start looking? Any tricks on how to tell if it's the primer on the fuel/water separator that is bad, or the lines themselves?

Thanks!

 

[Ronmar]

here is an overview of the cat 3116 fuel system and checking out the primer specifically. If you have a leak in the supply line or a leaking flapper check in the primer and a leak anywhere else, the fuel drains back to the tank as it doesn't have a foot valve on the supply line in the tank.

 

[Suprman]

I see bad fuel filter housings and cracked leaky feed lines from the tank. I would replace the main filter primer housing and the soft lines.

 

[jkcondrey]

Mine does this on occasion as well. 3116. I replaced the primer pump and filter, ran across my lines visually to look for seepage while it isn't running, no cracks. My brother in law that works for cummins suggested it was an injector oring leaking. It does seem to happen more often when it is cooler outside or has sat for awhile. But like you said, once it gets good flow, it off and running.

 

[SausageGuy]

When I got mine the fuel filter was off side of block and starter was in floorboard. Figured out the fuel lines from tank to separator were shot. They were so brittle they snapped like sticks when bent. Thats where they lost prime and burned up starter trying to get running.

 

[coachgeo]

....My brother in law that works for cummins suggested it was an injector oring leaking. ....

send sample of lump oil out for testing. They can tell you if there is more than normal amount of diesel in your lube oil. This will help diagnose if it is an injector leak or not.

 

[Ronmar]

with the cat design, I think you would be more likely to find fuel in the coolant or vis versa with a seal failure, then excess fuel in the oil. All diesels ultimately wind up with fuel in the oil, low engine loading and low op temps can cause more of this...

The MUI and HEUI injectors both need baseline fuel pressure to feed and operate correctly. If this thing is leaking/inducing air, as this air passes the lift pump it causes flucuations in base FP, and unstable injector firing. As this air then passes thru the gallery it will also interfere with injector firing Untill it passes the gallery.

This system has a few things working against it. the tank being lower than the head means when not running the system is always under negative pressure, so any leak anywhere above the tank means the weight of the fuel in the return line will cause it to siphon fuel down the return as the air gets sucked in. If the leak is in the supply line or if the flapper valve in the water sep/filter leaks it will flow back down both supply and return lines.

I think adding a 3-5 PSI check valve to the return at the tank and a plain check valve on the supply line at the pickup tube would make this system way more tolerant of tiny leaks and growing air bubbles while setting...

 

[fuzzytoaster]

Ronmar's videos are on point. Always replace the soft lines. I do them on Every. Single. Truck. If they don't look cracked it's just because you haven't seen the backside of them yet.

 

[jkcondrey]

What is everyone's main source for the fuel lines?

 

[coachgeo]

What is everyone's main source for the fuel lines?

answer would have bit you lol. It's at top of page via Wes Simpson's Parts spread sheet. Link to it is in sticky at top of this page. for fuel lines all below are listed

Parker PUSH LOK Brass Fitting Male 3/8" pipe for 3/8" hose	PARKER	30182-6-6B
Parker PUSH LOK Brass Fitting Male 1/2" pipe for 1/2" hose	PARKER	30182-8-8B
Parker PUSH LOK Brass Fitting Male 1/8" pipe to 1/4" hose	PARKER	30182-2-4B
Fuel Line 3/8" 350psi BLUE color varies last 3 of p/n	PARKER	801-6-BLU (by ft)
Fuel Line 1/2" 350psi BLUE color varies last 3 of p/n	PARKER	801-8-BLU (by ft)