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Leaky Lift Pump / Lift Pump Bolts


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If you notice drips of diesel after starting it's most likely your fuel system lift pump is leaking.  The lift pump pressurizes the CAPS pump (HPCR after 2004) for 60 sec after startup.  After that the lift pump shuts off leaving the CAPS pump (the expensive part) to suck fuel through 2 filters and all the lines back to the tank.  This is by design by Cummins.  If your lift pump is leaking then the CAPS pump is most likely sucking a small amount of air into the CAPS pump and into the injectors.  THIS IS VERY VERY BAD. 

2003 HR Endeavor, Cummins ISC Engine.  Access (on our coach) is through the narrow hatch in the bedroom, not the rear hatch in the back wardrobe.  You have to look straight down . . . kinda . . . 12-18"down between the transmission dip stick and the engine.  Lots of hoses & wire bundles will blind your vision.  You'll need to wedge a flashlight down into the bundles to see anything, otherwise the light just reflects back and you can't see anything. 

There's 3 bolts from above with 11 mm heads.  One is easy to see and can be snugged with a box wrench or socket (use a 1/4 drive, you'll thank me later).  Then one toward the rear on the inside (toward the engine).  If you get just the right viewing angle and have your light pointed just right you can see one flat of the bolt head.  You'll need a socket for this one and snake your arm down around the steel intake pipe (the big pipe at the top) and feel for it.  Don't let the socket come out of the ratchet.  I don't know what happens but chances are you'll never see it again.  The last one (inside toward the engine), way under the trans dip tube, is visible at just the right angle.

I tightened mine about 1/4 turn each. 

There's 2 allen head bolts on the top of the lift pump with 5 mm heads.  Leave these alone - they are ports into the fuel system. 

If you've got a LLP (leaky lift pump) and have been in denial (like me) this might get you over the hurdle to address it. 

- bob

Edited by cbr046
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  • cbr046 changed the title to Leaky Lift Pump / Lift Pump Bolts

I was aware of the potential of a leaking lift pump.  Cummins put out a Technical Service Bulletin on this, see attached, which listed replacement gaskets.  There are two styles depending on SN of engine/pump.  The gaskets can be bought on Ebay.  I actually bought one to carry just in case.

Then in late 2020 I found my pump leaking, tightened the bolts as you describe.  But after seeing numerous posts on this and a higher frequency of CAPS pumps failures I decided to just go ahead and install a FASS pump and bypass the old lift pump. 

Cummins ISL Lift Pumps service bulletin.pdf

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43 minutes ago, jacwjames said:

Then in late 2020 I found my pump leaking, tightened the bolts as you describe.  But after seeing numerous posts on this and a higher frequency of CAPS pumps failures I decided to just go ahead and install a FASS pump and bypass the old lift pump.

The leak started me down the same path.  I'll be ordering a FASS system this week.  Not sure yet if I'll bypass the old lift pump. 

- bob

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4 hours ago, cbr046 said:

The leak started me down the same path.  I'll be ordering a FASS system this week.  Not sure yet if I'll bypass the old lift pump. 

If you do (bypass the lift pump) you will need to install a resistor (10 ohm????) into the connector that powers the lift pump.  I found that the tube from the lift pump housing to the engine mounted fuel filter can be taken loose from the lift pump housing and rotated outboard, where you can install a #10 union (I used one with a 1/8" NPT port to add a pressure sending unit https://www.amazon.com/ACEFLOW-Adapter-Fitting-Pressure-Aluminum/dp/B088KMGCCQ/ref=sr_1_19 crid=1I6IVM5ETN3H5&keywords=10an+union+fitting&qid=1641154458&sprefix=%2310+AN+Union%2Caps%2C85&sr=8-19 ) and then attach the flexible rubber fuel supply hose to the #10 union.  No more worry with a leaky gasket (since it will be under constant pressure of the FASS pump). 

Ken

Edited by Cubflyer
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I did the same as Bob, tightened my 3 bolts with a 7/16 socket about a half turn each on my '02 350 horse Cummins ISC.  Could only see on drawing and feel, couldn't see to tighten.  Been over a year, no leaks.  I was impressed, they said it couldn't be done.

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