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.
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
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