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Old 09-05-2021, 04:41 PM   #1
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ISC lift pump fuse location?

Have a 2008 Cummins ISC on Freightliner M2 chassis. Engine cranks but does not start. Easy stuff first, does this engine have a fuse for the lift pump, is so where is it? If I have the hood up, should I be able to hear the lift pump run for a few seconds when the ignition key is turned on (but not cranking).
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Old 09-05-2021, 04:53 PM   #2
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Yes, the pump should run approx 30 seconds with each key on "wait to start" cycle. They are usually noisey enough to easily hear.
I believe the ECU has multiple "engine" fuses it utilizes. Ours are located in the main chassis 12v "ignition" fuse panel.
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Old 09-05-2021, 05:21 PM   #3
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Look for a couple of fuse holders at positive terminal at chassis batteries.
Maybe a smaller white wire on battery, a lot of ECM main power comes direct from batteries, with a inline fuse....

Did engine just shut down? Or you shut it down and now won't start?
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Old 09-05-2021, 05:43 PM   #4
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The RV was in its storage lot having returned from a trip a few days ago. Previously running well, no issues. Suspect a lift pump, or fuse, or ecu issue.
Ran continuity check on all fuses in two engine compartment fuse boxes, all were ok. Last resort, call Coach Net tow to the shop - at least itís free.
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Old 09-05-2021, 07:38 PM   #5
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First test pump wiring for 12V present while someone else turns on key, then run continuity test on both wires. You might have a short caused by rodents. The fuse wouldn't have failed without battery electricity present in storage.
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Old 09-06-2021, 09:19 PM   #6
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Eureka! It started late this afternoon. I heard the lift pump running and 15 seconds later it started right up. I have no idea what the problem was before. I tried starting it 5 or 6 times before I gave up. I donít recall listening for the lift pump previously, I just assumed that was probably the problem. Happy tonite, Iíll check it again tomorrow. In any case Iíll let the shop run diagnostics just to verify.
Thanks for your responses.
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Old 09-06-2021, 09:32 PM   #7
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Fuel system needs to be examined for leaks , even the slightest leak could allow air into the system and delay start up as the lift pump cycles to purge air and supply the injector pump with fuel .
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Old 09-07-2021, 07:39 AM   #8
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If you have an account set up on the Cummins Quickserve site you can look at the wiring diagram and see the relationship of the lift pump with the ECM.


There is a wiring harness on the bottom of the lift pump that you might check to make sure it is clean and the connection is tight. From there the wires go to the ECM, which you could also check. The ECM is protected by a number of fuses, in my case they are all located in my passenger side rear electrical bay.


The pump itself could be failing and might need to be replaced.
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Old 09-18-2021, 09:05 PM   #9
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Quote:
Originally Posted by jacwjames View Post
If you have an account set up on the Cummins Quickserve site you can look at the wiring diagram and see the relationship of the lift pump with the ECM.


There is a wiring harness on the bottom of the lift pump that you might check to make sure it is clean and the connection is tight. From there the wires go to the ECM, which you could also check. The ECM is protected by a number of fuses, in my case they are all located in my passenger side rear electrical bay.


The pump itself could be failing and might need to be replaced.
First tighten the 2 bolts on top the lift pump, these hold the pump and motor together with a gasket between them. The bolts work loose, pump sucks air. Things go downhill ($$$$) from there.
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Old 09-18-2021, 09:38 PM   #10
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Quote:
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First tighten the 2 bolts on top the lift pump, these hold the pump and motor together with a gasket between them. The bolts work loose, pump sucks air. Things go downhill ($$$$) from there.
3 bolts, would have little to do with the lift pump not running, but if it was it should drip fuel when those bolts are loose.
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Old 09-18-2021, 10:40 PM   #11
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Mike you should hear the lift pump motor run for 30 -45 seconds after turning on the ignition key. Then by design the ECM turns it off. This insures the main pump is primed and all air eliminated from the system. After the main pump is supplying the engine everything prior to the main pump is under negative pressure.

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3 bolts, would have little to do with the lift pump not running, but if it was it should drip fuel when those bolts are loose.
There are many lift pump threads involving loose retainer bolts, use the google search box above to find them.
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Old 09-18-2021, 11:03 PM   #12
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With the change from the CAPS fuel system in 2003 to HPCR , the lift pump and it's location changed . The lift pump bolted to the fuel manifold that caused the fuel leak issues with the CAPS system gave way to an inline pump mounted to a cooling plate behind the Cummins ECM.
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