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Old 28-04-2018, 09:03   #1
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Perkins 4108 Lift Pump Bypass

Has anyone successfully by passed the engine lift pump using an electric 12vdc pump installed just after fuel supply and befor the first filter with the output connected to the engine filter by passing the lift pump?
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Old 28-04-2018, 09:27   #2
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Re: Perkins 4108 Lift Pump Bypass

I just left my lift pump in place. But see no reason you couldnt just bypass it completely.
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Old 28-04-2018, 09:28   #3
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Re: Perkins 4108 Lift Pump Bypass

Yes, after going thru 2 lift pumps and one scary diesel runaway I put a Napa auto 12 volt fuel pump and ran it like that for several years with no trouble at all. Sold the boat still using the electric pump. It was easy to do. _____Grant.
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Old 28-04-2018, 09:34   #4
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Re: Perkins 4108 Lift Pump Bypass

I bypassed mine since it was the internal diaphram that failed and filled the sump with fuel. I didnt want any chance of leakage into the engine._____Grant.
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Old 28-04-2018, 09:35   #5
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Re: Perkins 4108 Lift Pump Bypass

Installed a inline electric pump, but did not bypass the lift pump.
Had an On-Off button on the electric pump. Used it for bleeding after filter changes and as a “go home” pump in case the lift pump failed.
My diesel guy installed it, rather expensive at $170, pump was for diesel trucks, heavy duty.
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Old 28-04-2018, 11:17   #6
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Re: Perkins 4108 Lift Pump Bypass

Electric inline pumps are on ebay for about $20. If the mechanical pump is dead, it's better to remove it and blank off the mount. If the diaphragm should rupture, the pressurized fuel would go into the sump.
I use them on 2 DDs and 2 generators. I carry a couple spares that fit any engine, but no failures yet.
Electric fuel pumps make bleeding much easier.
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Old 28-04-2018, 12:57   #7
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Re: Perkins 4108 Lift Pump Bypass

Just did it 2 months ago. Cut a piece of starboard to cover the lift pump opening and with a new gasket, sealed up the opening. Like others described, used a $9 12 vold pump wired to the ignition switch. Works fine. Bob
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Old 28-04-2018, 13:03   #8
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Re: Perkins 4108 Lift Pump Bypass

My brother has a 4108 but he hasnt heard of a lift pump - what is it?
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Old 29-04-2018, 09:31   #9
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Re: Perkins 4108 Lift Pump Bypass

I have a 12V fuel pump before 2 160 GPH Racore fuel filters. One is 10 micron and the other 5 micron, same as the 5 micron engine filter.
With valves I can run the engine one one filter or the other, allowing me to change filters w the engine running..
With a valve I can bypass the engine and polish my fuel.
I have not bypassed the engine fuel pump or filter for normal engine operation.
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Old 29-04-2018, 09:43   #10
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Re: Perkins 4108 Lift Pump Bypass

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My brother has a 4108 but he hasnt heard of a lift pump - what is it?
In some installations the Fuel Injection Pump requires fuel under pressure to keep it fed. The mfg normally uses a low pressure diaphram pump to meet the requirement. On many industrial installations the FIP pump is gravity fed and the LP feed pump is not required. Many BOSCH FI designed pumps have a low pressure pump built in so an external pump is not required. The term LIFT pump would be more appropriately named a FEED pump because that is its' function in the system.
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Old 29-04-2018, 09:55   #11
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Re: Perkins 4108 Lift Pump Bypass

On my Morgan 384 Perkins 4108 I installed a electric fuel pump right after the fuel filter 6 inches it forces fuel down the throat of my manual pump ! Wired to the key switch . And i carry a spare. I did the same thing to my generator. just a little helping hand for my old girl !
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Old 29-04-2018, 10:45   #12
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Re: Perkins 4108 Lift Pump Bypass

When I bought by CSY 33 6 years ago it had an electric pump installed but still had the lift pump.

All work well until I got a blockage in the fuel line just at the input to the electric pump. That's when I discovered the electric pump was installed before the Racor. I moved it to be after the Racor to prevent becoming blocked again.

Why would anyone install the pump before the filter?
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Old 29-04-2018, 10:48   #13
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Re: Perkins 4108 Lift Pump Bypass

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Originally Posted by wunderluster View Post
When I bought by CSY 33 6 years ago it had an electric pump installed but still had the lift pump.

All work well until I got a blockage in the fuel line just at the input to the electric pump. That's when I discovered the electric pump was installed before the Racor. I moved it to be after the Racor to prevent becoming blocked again.

Why would anyone install the pump before the filter?
Because pumps push far better than they suck. So if the racor is starting to get dirty a bit and requires more suck, your engine may starve. But, if it works it works!
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Old 29-04-2018, 15:36   #14
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Re: Perkins 4108 Lift Pump Bypass

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My brother has a 4108 but he hasnt heard of a lift pump - what is it?
Its a small engine driven pump that pumps diesel fuel to the injection pump.
Get a workshop manual and check it out.By the way i have a 4107 and have had lift pump failures,never had any fuel in the bilge.
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Old 29-04-2018, 15:42   #15
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Re: Perkins 4108 Lift Pump Bypass

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Its a small engine driven pump that pumps diesel fuel to the injection pump.
Get a workshop manual and check it out.By the way i have a 4107 and have had lift pump failures,never had any fuel in the bilge.
Right - we dont have fuel in the bildge but do have quite a bit of oil.

Just working on a oil pressure alarm issue after a overheat incident.

Low oil pressure even though have lots of oil - might be another thread?
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