# Generator Repair for Laguna Niguel owners Onan and Cummins generator diagnosis, service, repair and replacement, $400 to $8,500 and beyond across two to thirty five hours. The most common no start is a carburettor gummed by fuel left sitting, not an electrical fault. Load bank testing tells us what a no load run never can. ## Why an under exercised generator will not start A generator that will not start has one leading cause and it is not electrical. Gasoline left in a carburettor for two seasons evaporates and leaves varnish in the jets and the bowl, so the unit cranks, catches for a second on prime, and dies. Onan units in particular do this after a single winter of sitting. Diagnosis takes about half an hour: confirm fuel delivery at the pump, pull the bowl, look at the main jet, then check spark and compression. If the bowl is amber and the jet has closed down, the answer is a carburettor rebuild or replacement, not a control board. The fix owners do not want to hear is a schedule. A generator needs to run under real load for a couple of hours every month, and the units that fail belong to people who use the coach twice a year and never start it in between. Exercising it costs fuel. Not exercising it costs a carburettor, then a starter, and eventually valves, because the same fuel that gums a jet also washes down a cylinder wall. ## Exercise, oil, filters and the annual service Scheduled service on an Onan or Cummins unit is straightforward and gets skipped anyway, because the generator lives in a bay behind a door nobody opens. A service covers oil and filter, air filter, spark plugs on a gasoline unit, fuel filter, valve lash on the models that specify it, the slide tray rails where the unit is tray mounted, and a full inspection of the exhaust and the mounts. Hours meter and calendar are both used, whichever comes first, and the hours reading goes into the file every visit. Generator service and repair runs $400 to $8,500 and beyond across two to thirty five hours. A routine service sits at the bottom of that. The top is a unit neglected long enough to need a carburettor, a starter, an exhaust section and a control board in one visit, which happens more often than anybody would like. Deferring the service does not save money. It converts a predictable low number into an unpredictable high one, and it usually does that at the start of a trip. - Oil and filter, air filter, fuel filter, plugs where fitted - Valve lash checked against the model specification, not assumed - Exhaust tube, muffler and hangers inspected for internal corrosion - Mount isolators checked for collapse and cracking - Slide tray rails cleaned and lubricated on tray mounted units - Hours meter reading recorded in the job file ## LP, gasoline and diesel supply, and why they fail differently Three fuel arrangements exist and they break in different places. An LP unit draws vapour off the top of the tank through a regulator, so it has no varnish problem and starts happily after long storage, but it loses output on a nearly empty tank and will not run at all if the regulator has drifted. A gasoline unit on a motorhome usually draws from the chassis tank through its own pickup tube that sits well above the bottom, which is why it quits with fuel still showing on the dash gauge. A diesel unit shares that tank the same way and adds an air bleed procedure and a filter that will stop it dead once it loads up. Knowing which of the three is in the bay changes the first ten minutes of diagnosis and it changes the price. An LP no start is usually a regulator, a solenoid or ignition. A gasoline no start after storage is usually fuel. A diesel no start under load is usually filtration or air. LP work is handled only by a technician certified for gas, which the shop holds, and that is also why an LP job carries the $45 hazmat line. ## Load bank testing against a no load run A generator that starts and runs is not a generator that works. Owners test theirs by pushing the button, hearing it settle, and calling it good, which proves ignition and fuel at idle and nothing beyond that. Real testing puts a load bank on the output and holds it near rated capacity while voltage, frequency and exhaust colour get watched. Faults that only appear loaded include a worn stator, a failing capacitor on an inverter style unit, a slipping governor, a partially restricted fuel path, and an exhaust that is far more blocked than it looks from outside. Load testing also settles the argument about whether the generator or the air conditioner is at fault when a coach browns out on generator power. A unit holding 120 volts at 60 hertz under full load is not the problem, and the transfer switch or the compressor start circuit becomes the target instead. Testing in that order avoids replacing an expensive generator in order to fix a capacitor, which is a mistake we have seen arrive already made. - Output voltage and frequency held near rated capacity rather than read at idle - Exhaust colour watched through the whole loaded run - Governor response checked as load is applied and removed - Inverter style units checked for capacitor fade under sustained load ## Exhaust and mount corrosion in coastal air Coaches living within a few miles of the water in south Orange County lose their generator exhaust systems long before they lose the engine. Salt laden marine layer sits in the bay overnight, condensation collects inside a cold exhaust tube, and the tube rots from the inside out at its low point. The first sign is usually a smell of exhaust inside the coach at the bedroom end, which is a safety matter and not a comfort one. Mount isolators go the same way, and a collapsed isolator lets the unit shake its own wiring and fuel line apart. Exhaust and mount work is not expensive on its own, and it is exactly the line an owner asks to defer. This is the one place on this page where we push back, because carbon monoxide entering a sleeping area is a different category of risk from an inconvenience. Almost everything else on a generator can honestly wait for the next visit if money is tight this month, and we will help decide what waits. ## Auto start, remote panels and the wiring between them Remote start panels and automatic generator start controllers account for a surprising share of no start calls, and none of them are engine faults. The panel talks to the unit over a two or three wire harness running the length of the coach, and a corroded connector behind the dash produces a dead button and a perfectly healthy generator. Automatic start modules add their own logic on top: a low battery threshold, a temperature trigger, a time lockout. A module that believes the batteries are fine will refuse to start no matter what the owner wants. Testing that means jumping the start circuit at the unit itself. If it fires and runs from the bay, the engine is fine and the money belongs in the harness or the panel. Owners who have already bought a control board on a forum recommendation tend to discover this on the bench, after the part is opened and no longer returnable, which is a reason to test before ordering rather than after. ## Fitting a new unit into a bay that was not built for it A replacement is rarely a bolt in. Model lineups change, footprints change, and a bay built around a discontinued unit will be wrong in at least one dimension for whatever replaces it. Installation covers modifying or fabricating the tray, relocating the fuel pickup or the LP line, rebuilding the exhaust path so it exits where it should and not under a bedroom window, moving the output and control harness, and cutting and reframing the bay door opening when the new unit needs more air. Air is the part owners underestimate: a generator starved of cooling air will run beautifully and then shut down on high temperature every warm afternoon. Installation lands in the upper half of the band for those reasons, and on a coach with an awkward bay it reaches the top. Where the numbers get uncomfortable is a small trailer. Fitting a permanent unit into a travel trailer never designed for one often costs more than the trailer justifies, and a portable unit on a rack with a proper inlet is the sensible answer. We would rather say that than sell the install. ## Related - [class-a-diesel-pusher](https://ocrv.guru/vehicles/) - [class-a-motorhome](https://ocrv.guru/vehicles/) - [standard-fifth-wheel](https://ocrv.guru/vehicles/) - [food-truck](https://ocrv.guru/vehicles/) - [mobile-medical-unit](https://ocrv.guru/vehicles/) --- Source: https://ocrv.guru/services/mechanical-systems/generator-repair/ OCRV Center, 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. Serving Laguna Niguel, California. All work performed in shop. No mobile or roadside service. Licences: California Bureau of Automotive Repair ARD00288521; EPA CAL000367879. Published ranges are ranges, not quotes. Every figure traces to https://ocrv.guru/prices/.