Onan Generator Fuel Pump Troubleshooting

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Onan generators are one of the most popular choices for R.V. camping because they are built tough, are very reliable and have few problems in the long run. That’s exactly the type of generator every camper wants, no muss and no fuss. They start easy, they’ll run for hours, and they need very little maintenance. What more could anyone ask for?

However, no generator is perfect, not even an Onan. Above all else, any generator is reliable by the sum of its parts, fuel pumps notwithstanding. Whether through user error, an incompatible fuel being used, contamination, or if the engine is not running right regardless of the fuel pump, here are some symptoms and fixes for a possible fuel pump problem.

You may be surprised, but in many cases what appears to be a fuel pump issue, may not be related to the fuel pump at all.

The Engine

A fuel pump, literally, electrically pumps gasoline from the tank into the carburettor so that the engine can run. However, what might first seem to be a fuel pump issue might actually be an engine issue. Ask yourself this; When was the last time the spark plug was changed? When was the last time the air filter was cleaned or replaced? When was there last time the fuel filter was checked?

If the spark plug is old or fouled, the engine is going to run as if it was fuel starved, exactly the same symptom of a troublesome fuel pump. The same goes for a dirty air cleaner. Without adequate oxygen to breathe, an engine will run as if it is starved of fuel, which is, again, the exact same symptom of a bad fuel pump. Before you do anything else, put in a new spark plug and either change or clean the air filter.

Doing both is very inexpensive, and virtually anyone with DIY experience will be able to handle this task. Once that has been done, you may be pleasantly surprised to find that your Onan runs as good as new and that your suspicions about a bad fuel pump were the result of dirty or fouled components.

Although in most cases a fuel filter will last the life of the generator, in dusty situations when you are adding gas, or fuel madded from a dirty container, dirt and debris might inadvertently be introduced into the fuel system.

The fuel filter will prevent any harmful particles from getting into your carburettor and engine, but a plugged fuel filter will also mimic the symptoms of a faulty fuel pump. Replacing one may cure the problem.

Bad Gas

If you are the type of person who uses their generator seasonally, or stores it for long periods of time, bad gas or old gas in the tank is going to cause your engine to run as if the fuel pump is on its way out.

Your fuel pump might be pumping the correct amount of gas to the carburettor, but if the fuel has been sitting for a season or longer, or it has been contaminated, your engine may run badly, sputter, or seem like it isn’t getting enough fuel. That’s exactly the type of performance you would see if the fuel pump was not functioning properly.

Preventing this kind of issue is easy. Run the engine dry at the end of your camping season, and make sure the gas tank is fully drained. An alternative would be to pour in the correct amount of a fuel stabilizing product, then run the engine for a few minutes to ensure that the fuel stabilizer has entered the carburettor jets.

This should be done seasonally, or if you plan to put your generator into storage for a while. Doing this before the next time you start it up might make all the difference in the world.

Premium Fuel or Additives

If your generator begins to overheat or run noticeably harder under smaller loads, it is entirely possible that your fuel pump may be the problem.

It also is entirely possible that the fuel you have been using is beginning to gum up the works, from fuel pump valves, carburettor jets, and cylinder valves. You can check this out by using premium fuel, adding some small engine cleaning additive to your gas, or both.

This would generally apply more for older generator engines than newer ones, but even new engines, valves and cylinders can become fouled under the right conditions.

For example, if you are out in the middle of nowhere, and your only place to get fuel is at some old gas pump at a general store, or in another country, you really don’t know what type of gasoline you are putting in the generator’s gas tank. Who knows how long the fuel has been sitting there, and who knows how pure or contaminated it is.

Pouring in a fuel additive specifically made to clean smaller engines, or even using premium fuel, may clean or greatly improve both the fuel flow from the fuel pump and/or clear the carb jets and remove engine deposits. In both of these situations, your engine may run better, and if so, you will know it isn’t a fuel pump problem after all.

Mechanical or Electrical Problem

If you have tried everything above, and you are still having issues, the chances are that it is, in fact, fuel pump related.

There are 3 main reasons why an Onan fuel pump will not function properly. The fuel pump motor is going bad, the fuel pump valves are worn or clogged, or the electrical board that supplies the fuel pump with power has a glitch. Although rare, it is also possible that a power wire may have come loose.

The solutions to these issues are not that easy unless you have solid do it yourself experience. The first thing to do is to check the wiring connections and make sure they are attached and solid.

Make sure they aren’t corroded, and that there is no discoloration of the wires. Discoloration means the pump is drawing more juice and is on its way out.

Test the fuel pump motor itself by removing it and making sure it is drawing the correct amount of electrical current. If so, that rules out the motor going bad. Check to see how much liquid it pumps, using water.

If the motor is running correctly, but water dribbles out of the exit hose, the chances are that the inner valves are not working properly. Lastly, if you attach an artificial power supply to the fuel pump, and it runs correctly, the problem is most likely the electrical board.

With any known fuel pump issues, and if you have mechanical experience, it may be better just to replace the fuel pump itself. It’s a relatively simple task and can be done in less than an hour.

If your troubleshooting leads you to believe the electrical power board is shot, you would have to decide whether to tackle this one yourself, or take it into a certified Onan dealer and allow their service department to handle it.

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