8 Common Reasons Why Onan Generator Not Cranking and Solutions

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A generator produces electricity by running an engine that spins an alternator. The engine requires a battery, a starter motor, a spark plug, and a fuel system to operate. 

When you press the start button, the battery sends a current to the starter motor, which turns the engine over. The spark plug ignites the fuel-air mixture in the cylinder, creating a combustion that drives the piston. The piston moves the crankshaft, which rotates the alternator and generates electricity.

However, if any of these components are faulty or malfunctioning, the engine may not crank or start. This can be frustrating and inconvenient, especially if you depend on your generator for your power needs. Fortunately, most of the problems that cause an Onan generator not to crank can be diagnosed and resolved with some basic tools and knowledge.

In this blog post, we will cover the following reasons why an Onan generator may not crank and how to fix them: Let’s get started!

What Does It Mean When Your Onan Generator Won’t Crank?

onan generator wont crank

When your Onan generator won’t crank, it means that the engine is not turning over when you press the start button. This can be due to a problem with the electrical system, the fuel system, the ignition system, or the engine itself. Some of the symptoms of a generator that won’t crank are:

  • A clicking sound from the starter solenoid
  • A slow or weak cranking of the engine
  • No cranking or sound at all.
  • A flashing error code on the control panel

Now let’s look into the details of why this problem happens and what you can do to fix it. Firstly, you have to remove your Onan generator from your RV and jumpstart the generator if it will start. 

First things first, ensure the generator is filled with fuel and the oil is gauged. If they are, then you can proceed with the jumpstarting and other recommended solutions.

ALSO READ:- How to Troubleshoot Onan Generator Starter Problems

The Reasons Why an Onan Generator Won’t Crank and Their Solutions

Onan 5500 Marquis Gold Generator Spark Plug

1: Battery-Related Issues

One of the most common reasons why your Onan generator may not crank is a low or dead battery. The battery provides the power to turn the starter motor, which then spins the engine. If the battery is weak or drained, the starter motor will not have enough power to crank the engine.

To troubleshoot this problem, you will need a voltmeter or a multimeter to measure the battery voltage. The battery voltage should be at least 12.6 volts when fully charged. If the voltage is lower than that, you will need to charge the battery or replace it with a new one.

You should also check the battery connections and terminals for any signs of corrosion, dirt, or loose wires. Clean the terminals with a wire brush, and tighten the connections if necessary. A poor connection can also prevent the battery from delivering enough power to the starter motor.

ALSO READ: 6 Top Reasons Why Onan Generator Dies Under Load And Their Solutions 

2: Faulty Starter Motor

Another possible cause of not cranking is a faulty starter motor or solenoid. The starter motor is an electric motor that engages the flywheel and rotates the engine. The solenoid is a switch that activates the starter motor when you turn the ignition key. If either of these components is damaged or worn out, the starter motor will not work properly.

To troubleshoot this problem, you will need to test the starter motor and the solenoid with a voltmeter or a multimeter. First, disconnect the negative cable from the battery and remove the wires from the starter motor and the solenoid. 

Then, connect the positive lead of the voltmeter to the positive terminal of the starter motor and the negative lead to the metal frame of the generator. 

Turn the ignition key to the start position and check the voltage reading. It should be around 12 volts. If the voltage is lower or zero, the starter motor is faulty and needs to be replaced.

Next, connect the positive lead of the voltmeter to the small terminal of the solenoid and the negative lead to the metal frame of the generator. Turn the ignition key to the start position and check the voltage reading. It should also be around 12 volts. If the voltage is lower or zero, the solenoid is faulty and needs to be replaced.

Alternatively, you can also use a screwdriver to bypass the solenoid and test the starter motor. To do this, disconnect the negative cable from the battery and touch the tip of the screwdriver to the large terminal of the solenoid and the metal frame of the generator. This will create a direct connection between the battery and the starter motor. If the starter motor spins, the solenoid is faulty. If the starter motor does not spin, the starter motor is faulty.

ALSO READ: Onan Generator Only Runs When Holding the Start Button: Causes, Solutions, and Troubleshooting Guide

3: Dirty or Faulty Spark Plug

A dirty or faulty spark plug can also prevent your Onan generator from cranking. The spark plug is a device that ignites the air-fuel mixture in the combustion chamber of the engine. If the spark plug is dirty, corroded, or damaged, it will not produce a strong enough spark to start the engine.

To troubleshoot this problem, you will need to remove the spark plug from the engine and inspect it for any signs of wear or damage. You can use a spark plug tester or a multimeter to check the spark plug for continuity and resistance. The spark plug should have a resistance of about 5,000 ohms and produce a bright blue spark when connected to the battery.

If the spark plug is dirty, you can clean it with a wire brush or a spray cleaner. You should also check the spark plug gap and adjust it if necessary. The spark plug gap is the distance between the electrodes of the spark plug, and it should be between 0.025 and 0.030 inches. You can use a feeler gauge or a spark plug gap tool to measure and adjust the gap.

If the spark plug is damaged or worn out, you will need to replace it with a new one. Make sure to use the correct type and size of spark plug for your Onan generator model. You can find the spark plug specifications in your owner’s manual or on the Onan website.

Apart from the spark plug not generating sparks to crank the engine, other factors such as the spark plug wire, the ignition coil, or the ignition switch will be explained next. 

ALSO READ: Onan 5500 Marquis Gold Generator Spark Plug

4: Faulty Ignition Switch

A faulty ignition switch is a device that connects the battery to the starter motor and the ignition system. If the ignition switch is defective, it may not send the signal to start the generator. You can test the ignition switch with a multimeter or a jumper wire. If the ignition switch is faulty, you will need to replace it with a new one.

5: Clogged Fuel Filter

A clogged fuel filter can also cause your Onan generator to not crank. The fuel filter is a device that filters out any dirt, debris, or water from the fuel before it reaches the carburetor. If the fuel filter is clogged, it will restrict the flow of fuel to the engine and prevent it from starting.

To troubleshoot this problem, you will need to locate the fuel filter on your Onan generator and remove it from the fuel line. You can use a pair of pliers or a wrench to loosen the clamps or fittings that hold the fuel filter in place. Be careful not to spill any fuel, and have a container ready to catch any excess fuel.

You can inspect the fuel filter for any signs of clogging or damage. You can also blow through the fuel filter to see if there is any resistance. If the fuel filter is clogged or damaged, you will need to replace it with a new one. Make sure to use the correct type and size of fuel filter for your Onan generator model.

ALSO READ: How to Clean Generator Fuel Filter in 8 Simple Ways 

6: Fuel Supply Issues

Fuel supply issues refer to any problems that affect the amount or quality of fuel that reaches the engine. Some of the common fuel supply issues are low fuel levels, stale or contaminated fuel, or air in the fuel line.

To troubleshoot this problem, you will need to check the fuel level and quality of your Onan generator. You can use a dipstick or a gauge to measure the fuel level in the tank. The fuel level should be above the minimum mark and below the maximum mark. If the fuel level is too low, you will need to add more fuel to the tank.

You should also inspect the fuel for signs of staleness or contamination. Stale fuel is fuel that has been stored for too long and has lost its volatility. Contaminated fuel is fuel that has been mixed with water, dirt, or other substances. Both stale and contaminated fuel can cause poor combustion and performance issues. If the fuel is stale or contaminated, you will need to drain the tank and fill it with fresh fuel.

You should also check the fuel line for any signs of air or leaks. Air in the fuel line can prevent the fuel from reaching the carburetor and the engine. Leaks in the fuel line can cause fuel loss and fire hazards. If the fuel line has air or leaks, you will need to bleed the air or repair the leaks.

7: Broken Flywheel Key

A broken flywheel key is a less common problem that might cause your Onan generator not to crank, which can only be fixed by a professional.

It is a small metal piece that aligns the flywheel and the crankshaft. The flywheel is a large wheel that stores rotational energy and helps the engine start. 

The crankshaft is a rod that connects the pistons and the flywheel. If the flywheel key is broken, the flywheel and the crankshaft will not rotate in sync, and the engine will not crank. 

You can inspect the flywheel key by removing the flywheel cover and the flywheel. If the flywheel key is broken, you will need to replace it with a new one if you can do so, but that should be the least to think of.

ALSO READ: Onan Generator Service Near Me: Reliable Way To Find One

8: Engine-Related Issues

Engine issues can also prevent your Onan generator from cranking. Some of the possible engine issues are a low oil level, a faulty oil pressure switch, a seized piston, or a broken connecting rod. These issues can damage the engine and make it hard or impossible to turn over.

To troubleshoot these issues, you will need to check the oil level and quality of your Onan generator. You can use a dipstick or a gauge to measure the oil level in the crankcase. The oil level should be between the low and high marks. If the oil level is too low, you will need to add more oil to the crankcase.

You should also inspect the oil for signs of contamination or degradation. Contaminated oil is oil that has been mixed with water, fuel, or metal shavings. Degraded oil is oil that has lost its viscosity and lubrication properties. Both contaminated and degraded oil can cause engine wear and damage. If the oil is contaminated or degraded, you will need to drain the oil and replace it with fresh oil.

You should also check the oil pressure switch, which is a device that monitors the oil pressure in the engine. The oil pressure switch is connected to the ignition system and will shut off the engine if the oil pressure is too low. If the oil pressure switch is faulty, it may prevent the engine from starting even if the oil level and quality are good. You can test the oil pressure switch with a multimeter or a jumper wire. If the oil pressure switch is faulty, you will need to replace it with a new one or bypass it, but this is not advisable.

If the oil level, quality, and pressure are all good but the engine still does not crank, you may have a more serious engine issue, for which we recommend you call a professional for assistance. Such problems include a seized piston or a broken connecting rod. These issues can cause the engine to lock up and stop rotating. 

A seized piston is a cylindrical part that moves up and down in the cylinder and compresses the air-fuel mixture. The piston is connected to the crankshaft by a connecting rod. If the piston is seized, it means that it is stuck in the cylinder and cannot move. 

This can happen due to overheating, a lack of lubrication, or dirt accumulation. You can diagnose a seized piston by removing the spark plug and trying to manually turn the engine with a wrench or a socket. If the engine does not turn, you may have a seized piston. 

To fix a seized piston, you will need to disassemble the engine and free the piston from the cylinder. Depending on the extent of the damage, you may need to repair or replace the piston, the cylinder, or the entire engine.

Engine issues are often the result of poor maintenance or overloading the generator. To prevent engine issues, you should follow the recommended maintenance schedule and service intervals for your Onan generator model. 

You should also avoid running the generator at full load for prolonged periods or exceeding the rated capacity of the generator. By doing so, you can extend the life and performance of your Onan generator.

Finally, if you’ve checked everything and it seems fine but the generator still won’t crank, then you have to check the generator wiring to see if any wires are contacting each other. By doing this, you can start your Onan generator. 

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