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Topic: Replaced leaking lift pump - dying engine (Read 2268 times) previous topic - next topic

Re: Replaced leaking lift pump - dying engine

Reply #20 –
Unless he means going back to the fuel tank.

Re: Replaced leaking lift pump - dying engine

Reply #21 –
Quote from: Jack Lewis –
When you say "hand priming slowly produces diesel fuel to the overflow", where is your overflow, are you loosening one of the injector lines and then re tightening?
Most all diesels except some CATs, return the majority of fuel to the fuel tank. There is a spring loaded valve, either located at the injection pump or in our case after the last unit injector to keep pressure and not allow fuel to run to the tank after the engine is shut off making it much harder to start the next time. It's a must to keep the fuel system full without letting air into the system.

A good hand pump will generate more pressure than the relief valve allows so will send the excess fuel back to the tank.

This return/relief valve can wear, get deposits on it, etc. This is a reason to occasional check to see if it's leaking and not allowing specified pressure to be in the injection pump. Low pressure will cause a loss of power and hard starting plus may cause increased wear due to insufficient lubrication.

This is one of the reasons that I installed a pressure gauge on the output side of the secondary filter. Other reasons include filter conditions as well as lift pump operation.

This is what a Bosch overflow valve looks like on a Bosch "P" pump: Amazon.com: 1417413047 Disel Pump Overflow Valve for Dodge Cummins 5.9L...

Most all diesels need them from simple mechanical diesels to cutting edge high pressure common rail engines. A video to explain them here:
https://www.youtube.com/watch?v=Hxpq1LfG584

Pierce
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Re: Replaced leaking lift pump - dying engine

Reply #22 –
Quote from: Pierce & Gaylie Stewart –
This is what a Bosch overflow valve looks like on a Bosch "P" pump: Amazon.com: 1417413047 Disel Pump Overflow Valve for Dodge Cummins 5.9L...
Thanks, Pierce, for the excellent video link!  They do make it sound like the valve they are discussing only comes into play when occasional high fuel pressure conditions exist.  On the Cummins engine (with mechanical lift pump and P7100 injection pump) the overflow valve is always actively working to keep fuel pressure constant anytime the engine is running.  It is just a ball & spring valve.  The spring can weaken over time, allowing the fuel pressure to decline to less than optimum levels.  Trash can block the ball from seating.  Either condition will adversely affect fuel pressure.

If anyone is going to all the trouble (yes, it's a tough place to get at) of checking/cleaning/replacing the overflow valve on a Cummins with P7100 injection pump, then double down yer bet and install the ADJUSTABLE valve from Tork Tek.  Well worth the extra cost.

Cummins Adjustable Overflow Valve by Tork Tek - OFV010

See my shiny OFV010 valve in the photo below (add some BLING to your drab old engine):
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Re: Replaced leaking lift pump - dying engine

Reply #23 –
While your at it get the gauge adaptor they have,easy to check fuel pressure.

Re: Replaced leaking lift pump - dying engine

Reply #24 –
Familyrig, did you ever find the air leak that was causing your diesel to loose prime?