Cummins Lift Pump Leakage Due to Ultra Low Sulfur Diesel Fuel - Engine Builder Magazine
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Cummins Lift Pump Leakage Due to Ultra Low Sulfur Diesel Fuel


Cummins has issued a caution regarding a potential lift pump fuel leak if a customer switches to Ultra Low Sulfur Diesel (ULSD) fuel after using Low Sulfur Diesel (LSD) fuel. This information affects Cummins ISB and QSB CM550, ISC, QSC, ISL, and QSL CM554 engines.

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The manufacturer of these engines says that due to fuel changes from LSD to ULSD, the lift pump can leak between the bracket and the lift pump body or at the electrical connector. If a fuel leak appears on the lift pump, determine if the customer has begun to use ULSD fuel recently.

Engine Family                  Fuel System

6B, B5.9                             Bosch VP44 – ISB

6C, C8.3                            CAPS – ISC, QSC8.3, ISL, QSL9

ISL, QSL9                          Bosch VP44 – ISB

Design Application         Market Application

Automotive                        All

Industrial                           Agriculture

Industrial                           Construction

Marine Propulsion             Marine

The suspected cause, according to Cummins, is a nitrile gasket between the lift pump body and the bracket. Once the nitrile gasket absorbs fuel, the gasket expands and seals. If the fuel type is changed from LSD to ULSD, the nitrile gasket will shrink and no longer seal, causing a fuel leak.



To avoid fuel leaks when changing to ULSD fuel, customers ought to consider replacing the lift pump as well. The table below lists the present part numbers for 12-VDC and 24-VDC lift pumps.

Lift Pump Part Numbers

Engine Family                 VDC     Part Number

ISC, ISL, QSL, QSC         12       3949085 and 3939894

ISC, ISL, QSL, QSC         24       3939898 and 3949086

ISB, QSB                          12       3990105

ISB, QSB                          24       3990106 


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