Why does my Westerbeke 44A stall and trip the 20-amp engine breaker?
After starting my Westerbeke 44A Four, it runs rough at idle at first, then calms down and runs as it should. Shortly after, it starts to struggle and choke out, stalls completely, and then the 20-amp breaker on the engine trips. What is causing this sequence?
Answer
Your Westerbeke 44A Four is suffering from a failing 12V electric fuel lift pump that overheats, draws excessive current and trips the 20-amp engine breaker. When the pump seizes and the breaker pops, the engine starves of diesel and stalls.
Electric Fuel Lift Pump Circuit
Unlike marine diesels with camshaft-driven mechanical lift pumps, Westerbeke engines rely on a 12V electric lift pump. This cylindrical Facet-style solid-state pump mounts low on the engine block or nearby on a bulkhead. It pulls fuel from the tank and pushes it through the secondary filter to the mechanical injection pump.
When these electric pumps age, their internal coils break down. On a cold start, the pump works just well enough to supply fuel. This initial weak pressure explains the rough idle. As the pump runs, it heats up. The internal resistance drops, causing the pump motor to short out and draw massive current. This electrical spike trips the 20-amp breaker mounted on the engine. The moment the breaker trips, the pump stops, fuel pressure drops to zero and the engine stalls.
Testing the Lift Pump
To confirm the lift pump is at fault, isolate it from the engine electrical harness.
- Locate the electric lift pump and disconnect the positive and earth wires.
- Run a temporary jumper wire fitted with a 5-amp inline blade fuse directly from the battery positive terminal to the pump positive lead. Connect the earth wire to a clean bolt on the engine block.
- If the pump clicks rapidly and runs smoothly for 15 minutes, it is healthy. If it blows the 5-amp fuse as it warms up, the pump is shorting internally and must be binned.
A genuine Westerbeke replacement pump costs around £130. A standard marine-grade Facet cylindrical pump with a 4 to 7 PSI rating costs about £50 and does the exact same job. After fitting the new pump, use a 10mm spanner to open the bleed screw on the secondary fuel filter housing. Bleed the air out of the system before restarting.
Oil Pressure Switch and Wiring
If the lift pump tests perfectly, check the wiring loom. Westerbeke engines use a safety circuit that routes power for the lift pump through an oil pressure switch. This switch is normally open. It only closes to send power to the fuel pump once the engine builds 15 PSI of oil pressure.