Why Is My Onan RV Generator Surging?

What surging sounds and feels like

Surging — often called hunting — is a rhythmic rise and fall in engine speed. The generator does not settle at a steady note. You hear it cycle up and down, sometimes once a second, sometimes slower.

Inside the coach you may notice lights pulsing in time with the engine, air conditioning that cycles oddly, or electronics that behave strangely because voltage and frequency are moving with the RPM.

Common contributing causes

• Fuel restrictions anywhere between the tank and the engine
• Carburetor metering problems, including partially blocked jets and passages
• Old or degraded fuel
• Air/fuel mixture problems, including air leaks that lean the mixture
• Governor behavior on units with mechanical or electronic speed governing
• Load conditions — some units behave differently unloaded than loaded
• Deferred maintenance: plugs, filters and stale fuel
• Other mechanical or electrical faults affecting engine speed or excitation

When it surges tells you something

What not to do

Do not run the generator for extended periods while it is surging, and do not attempt to compensate by holding the choke on. Do not disable or bypass shutdown protections to keep it running. If the unit is powering sensitive electronics, unstable output is a reason to shut it down rather than keep going.

How surging is diagnosed

The useful sequence is to confirm the maintenance basics, evaluate fuel quality and delivery, then observe the behavior under controlled load. Surging is a system symptom, so testing under the conditions where it occurs is the only reliable way to find which part of the system is actually responsible.