Onan Generator Won't Stay Running: Complete Repair vs Replace Guide 20

Quick Take

Since you've already "dropped lots of money" into your Onan generator and it still won't stay running for extended periods, it's time to make a strategic decision rather than continuing to throw money at intermittent fixes. Based on your frustration with multiple service calls, I'd recommend either a complete rebuild or replacement over continued piecemeal repairs. A refurbished unit from a reputable dealer like PPL Motor Homes, Camping World, or RV Parts Country typically costs $2,500-4,500 depending on your model (prices vary by region and specific model requirements), while a rebuild runs $1,500-3,000. Given that you're new to RVing and want reliability, a refurbished unit with warranty might be your best bet for peace of mind.

Common Causes

Onan generators that won't stay running commonly suffer from a few chronic issues that can be expensive to chase down individually. Common causes include fuel system problems, including a failing fuel pump (especially the mechanical lift pump), clogged fuel filters, or carburetor issues with the float or needle valve. The fuel pump alone can cost $300-500 in parts and labor, while carburetor rebuilds run $400-600.

Ignition system failures are another frequent cause, particularly worn spark plugs, faulty ignition coils, or timing issues. If your generator starts but dies after warming up, the problem could be heat-related expansion in electrical components or a failing temperature sensor. Control board issues can also cause erratic running, and these boards cost $400-800 to replace.

Air intake problems, including dirty air filters or carbon buildup in the combustion chamber, can cause poor running and frequent stalling. If multiple systems are failing simultaneously, it often indicates the generator has reached the end of its cost-effective service life, which is typically around 15-20 years or 3,000-5,000 hours under normal maintenance conditions.

Preparation

SAFETY WARNING: Before performing any diagnostic work, disconnect all electrical power and shut off fuel supply to prevent electrical shock or fire hazards.

Before making your final decision, gather some key information to help determine your best path forward. First, identify your exact Onan model number from the nameplate on the generator housing - this will be something like "4.0KY-FA/26100" or similar. Write down the spec number, serial number, and manufacture date as well, since this determines parts availability and compatibility.

Calculate your total investment so far by adding up all the money you've spent on repairs, parts, and service calls. Compare this to the cost of your options: a basic rebuild typically costs 40-60% of replacement cost, while a quality refurbished unit runs about 60-80% of new generator pricing. If you've already spent more than 50% of replacement cost, it's usually more economical to replace.

Research reputable suppliers in your area or online. For new units, authorized Onan dealers like Cummins Power Generation provide full warranty support. For refurbished units, companies like Norwall PowerSystems, RV Generator Doctor, and select Camping World locations offer rebuilt generators with 1-2 year warranties. Always verify the warranty terms and what's covered before purchasing.

Consider your RV's electrical needs and available space. Measure your current generator compartment dimensions and note any special mounting requirements. If you're upgrading, ensure your RV's electrical system can handle a different output rating, and check that fuel and exhaust connections will align properly.

Repair Steps

SAFETY WARNING: Disconnect power and fuel before performing any testing or diagnostic work on electrical and fuel system components.

If you decide to attempt one final diagnostic before replacement, start with the most common failure points that cause intermittent running issues. **FUEL SYSTEM WARNING:** Ensure adequate ventilation when working on fuel system components. Fuel vapors are highly flammable and can ignite from spark or heat sources. Begin by checking fuel delivery: use an approved fuel collection container (metal or anti-static plastic) positioned to catch all fuel spillage, ensure fire extinguisher is within reach, remove the fuel line at the carburetor and crank the engine briefly to check if fuel pumps out steadily. Weak or intermittent fuel flow usually indicates a failing fuel pump or blocked fuel pickup in the tank.

Test the ignition system by checking for consistent spark at both spark plugs while the engine is running and when it starts to stumble. Use an inline spark tester rather than just pulling the plug wire, as this maintains proper load on the ignition system. Ensure proper grounding and use insulated tools when handling ignition components. Intermittent spark often points to failing ignition coils, especially when the problem worsens as the engine heats up.

Clean or replace the air filter and inspect the exhaust system for obstructions. Carbon buildup in the muffler can cause backpressure that prevents proper running, especially under load. Remove the spark arrestor screen from the muffler (if equipped - varies by model) and clean it thoroughly, or replace it if damaged.

If these basic checks don't reveal the problem, you're likely looking at internal engine issues, control board problems, or complex fuel system repairs that will require professional diagnosis. At this point, the cost of proper troubleshooting and repair typically exceeds the value of continuing to fix an aging generator.

When to Get Help

Given your situation with multiple failed repair attempts, it's time to consult with a generator specialist rather than general RV service technicians. Contact an authorized Onan service center for a comprehensive evaluation - they can often diagnose complex intermittent problems that general mechanics miss. Ask for a written estimate that includes all likely repairs, not just the obvious ones.

For replacement options, start with these reputable suppliers: PPL Motor Homes (pplmotorhomes.com) offers a wide selection of new and refurbished generators with good warranty support. Norwall PowerSystems (norwallpower.com) specializes in rebuilt Onan generators and provides detailed specifications for each unit. RV Parts Country and Camping World also carry refurbished units, though selection varies by location.

When shopping for a refurbished generator, insist on seeing maintenance records and ask specifically what components were rebuilt versus simply cleaned. A proper rebuild should include new rings, gaskets, fuel system components, and electrical parts. Expect to pay $2,500-4,500 for a quality 4-7kW refurbished unit with at least a one-year warranty (prices vary significantly by region and specific model requirements).

Consider hiring a qualified RV technician for the installation even if you're handy with tools. Generator replacement involves fuel lines, electrical connections, exhaust routing, and proper mounting that must meet safety codes. Professional installation typically costs $500-800 but ensures everything is done correctly and maintains your warranty coverage.