RV Generator Maintenance, how to replace the Fuel Pump and Fuel Filter

RV Generators require Maintenance

Having a functioning power generator in your RV is such a luxury for the owner that most Motorhome owners, especially, cannot imagine not having one for their travels.

Generator Failures

But, of course, a generator is a mechanical device and it requires a certain amount of maintenance and care at times.

And Preventive Maintenance is a very important task that must be performed to keep your Generator in top shape.

But we all must accept the fact that all mechanical devices will eventually break down, even if they are maintained properly. So every RV owner that has a generator should be prepared to have certain things go bad, eventually.

Of course, it's always the hope of the owner that they have taken good care of their generator with an effective PM program so that when something does go bad, it will be a relative cheap repair job and the generator will not be severely damaged.

Standard Onan RV generator

A standard Onan Model-5500 RV gas-powered generator.
A standard Onan Model-5500 RV gas-powered generator. | Source

My RV generator Fuel Pump died

Recently, my generator stopped operating on me. It has a little over 500 hours on the meter, but it has always been maintained properly.

In fact, it had been running fine and then it just stopped running. I could crank it, but it would not fire up, at all.

I had to fix this, of course, so I went through a thorough trouble shooting procedure to confirm my suspicion that I had a bad Fuel Pump.

Onan Gas Generator Fuel Pump and Filter

View of the Fuel Pump and Fuel Filter on an Onan 5500 RV generator.
View of the Fuel Pump and Fuel Filter on an Onan 5500 RV generator. | Source

Trouble Shooting my RV Generator

I won’t go into all of the the details but, I went through a thorough trouble shooting procedure and eventually confirmed that the fuel pump for my generator was actually bad.

Of course, during my diagnostics, I had removed the cover of the generator and determined that;

  1. there were no loose connections visible,
  2. there were no leaking fluids,
  3. the motor had oil in the reservoir,
  4. the DC power source was good,
  5. and the filter was clean, etcetera.

This, in my opinion, is always the first step the owner should take when trouble shooting; remove the obvious from the list of potential problems.

Onan Fuel Filter, the #1 problem with RV generators

Finding the Fule Pump

And I discovered one other thing; My generator was an Onan model built for motorhomes and they had not included the full pump inside the generator compartment.

Rather, for some unknown reason they had decided to mount the fuel pump and the fuel line filter onto the underside of the generator base plate.

I should note here that over the years, these generator manufacturers can change their designs numerous times.

They might make a core generator, like mine that is a 5500-Watt model, and then have a dozen or more configurations of the basic generator to fit numerous applications.

For instance, where mine is set up for my motorhome, the same core generator unit might also be configured as; a portable model on wheels, a Home backup power source, a remotely-controlled model for remote site backup power, or any of dozens of other special applications.

Some of these specialty designs require that some of the peripheral parts like; fuel pump, fuel filter, carburator, air filter, oil drain and input, along with other specialty parts be different themselves or as is often the case, mounted in different positions.

The position of the fuel pump and fuel filter on my RV though meant that; to replace the fuel pump, or even just to replace the fuel filter, you had to get under the RV and work while lying on your back. I didn’t like this, but it was what had to be done.

View of Fuel Cut-Off Valve

View of the Fuel Cut-Off valve on an Onan 5500 Gas RV Generator
View of the Fuel Cut-Off valve on an Onan 5500 Gas RV Generator | Source

Ordering the Fuel Pump

Here is where I mention that one of the great things about having a smartphone is that you always have a good camera at hand, at all times.

So, even before I looked at the generator manuals, I crawled under my RV and took several pictures of the fuel pump and the fuel filter that showed the labels as well as how they were mounted.

This saved me a lot of time when it later came time, to actually change these parts.

Back home and with all of my data at hand, I sat down with my specific part numbers and pictures and shopped the web for the best deal on the parts I needed.

It turned out that Amazon gave me the best price and I was able to get free shipping within 5-days of placing the order. So, I ordered the parts and later, when I finally received them, it was time for me to get these new parts installed and my generator running again.

New Fuel Pump and Fuel Filter, installed

After installation, the new Fuel Pump and Fuel Filter looked like this.
After installation, the new Fuel Pump and Fuel Filter looked like this. | Source

Installation of the new Parts

Safety First:

Here is where I must mention that when you work on a machine, such as my gas-powered generator, there are certain safety procedures you should follow.

My generator was no exception, so I disconnected the 12-VDC to the generator, shut off the fuel lines, and I also followed the other manufacturers requirements listed in the owners manual.

Once all of this was done, I was ready to perform the actual replacement.

Tools Required

Because I had my pictures, I was able to determine the tools I would need for this job, so once I checked these pictures I saw that there were actually only a few tools needed;

  • 1- flat-blade screwdriver (for the hose clamps)
  • 1- Crescent wrench (for disassembling the fuel pump and fuel filter from each other).
  • 1- 5/16 socket and wrench set (for the two bolts that held the fuel pump to the base plate).
  • 1- 1/4-inch diameter wood dowel ( or other device, to plug the fuel line from the fuel tank).
  • 1- short piece of plumber’s tape (to assure a good seal between the fuel pump and the filter).

Knowing this ahead of time allowed me to only take the tools I would need and not have to haul a large toolbox full of tools to my RV.

Fuel Pump Replacement Procedure

There are probably a number of procedures that work, but, here is the replacement procedure I followed;

Considering that the fuel pump and the fuel filter were on the underside of the generator, I checked and saw that there were only two things I had to disconnect on the upper side of the generator;

  1. the two wires that provided power to the fuel pump,
  2. and the actual output fuel line from the fuel pump to the input of the fuel cut-off valve that is inline to the carburetor of the generator.

So, I disconnected both of them first of all.

The Replacement Process itself;

  1. I crawled under the RV and removed the fuel line from the fuel filter and stuck a piece of the wood dowel into the hose to prevent it from dripping on the ground and me.
  2. I then removed the two screws that held the fuel pump in place with the socket wrench.
  3. Carefully, I pulled the two wires and the fuel line down with the fuel pump-fuel filter combination and with it in hand, crawled out from under the RV.
  4. At this point, I assembled the new fuel filter to the new fuel pump making sure that the connection was sealed well wit a piece of plumber’s tape.
  5. Then I pulled the short piece of fuel line on the output of the old fuel pump and attached it to the output of the new fuel pump, using the same hose clamp.
  6. I took the time and compared the two assemblies to make sure they were essentially the same dimensions and that the new one should fit properly. At this point, I crawled back under the RV and worked the two wires and the fuel hose up and through the two hole the others had been in.
  7. I then mounted the new fuel pump where the other one had been with the same bolts.
  8. I connected the fuel line from the fuel tank to the input of the new fuel filter and reused the same hose clamp on this.
  9. Then, checking that everything fit properly and was firmly mounted, I crawled back out from under the RV.
  10. All that remained now was for me to reconnect the two wires, and then slip the end of the hose from the fuel pump to the input connection of the cut-off valve. I reused the same hose clamp on the hose connection.
  11. With this all done, I had finished the replacement of the fuel pump and fuel filter without incident, so I reconnected the 12-VDC and generally made the generator ready for testing my replacement parts with my generator.

Replacement Exhaust pipe Hanger

Generator Quick Test

I was now ready to run a quick test on the generator to assure that my new parts were the problem and the generator was now operating properly.

Using the two position switch that is installed with my generator ( with a parallel one on the RV dash), I pressed the lower section and primed the generator (see operators manual if you are not familiar with this commonly used switch), noting that the pump was making a sound and vibrating.

Then I pressed the other side of the switch to start the generator, After a couple of seconds of cranking, the generator fired up and started idling.

I then let the generator run for almost ten minutes.

Because it was running evenly after that period of time, I went inside and checked that my RV Power Control Panel indicated that I had 50-Amps service and that power was available for ALL of my AC appliances.

I then turned on one of my Air Conditioners (tocheck the generator under a load) and after the AC had cycled and was running properly, I went outside and watched my generator run for a couple of more minutes as the overall load shifted on and off with the AC conpressor.
The generator seemed to be operating properly after several minutes of operation, under load, so I pronounced my task done.
I went inside, shut down the AC, and turned off the generator. I was now ready for my next trip confident that i had a functional AC generator in my RV ready to provide me with the comforts i am used to.

by Don Bobbitt, August, 2015

How to Trouble Shoot Onan Gas RV Generator

Onan 5500 RV Generator Maintenance

© 2015 Don Bobbitt

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