Onan Cummings 5500 EFI Generator

[smitty31093]

FYI, If you buy a trailer that is "prepped" for an Onan generator be aware that it is only prepped for a carburetor generator. I recently bought an Onan 5500 Electronic Fuel Injected (EFI) generator for my 2016 Vengeance 320A Toy Hauler. The generator looks just like a carburetor model and bolts up in the trailer exactly the same. The differences are in the fuel lines and the fact that the EFI units have to have an external electric fuel pump. The carburetor units only need a fuel supply line and a return line to the catalytic vapor canister for fuel vapors (only). My EFI unit has to have a fuel supply line and a return to fuel tank line for liquid fuel. Since I didn't know this, I had two fuel line barbs on my generator set (1/4" and 5/16") and the prepped hoses on my trailer were the same sizes. I naturally connected the small hose to the small barbed fitting and the larger hose to the larger barbed fitting on my generator. The generator would not prime nor start. Convinced the generator was not getting fuel, I dropped the fuel supply line into a 5 gallon gas can. The generator primed and started immediately and ran like a champ. The generator quickly sucked the gas can dry and returned most of the gas to the on board fuel tank just like it was designed to do. I talked to the techs at Camper's Inn in Byron, GA where I bought my trailer and they told me to reverse the fuel lines. I used some adapter fittings and changed the large hose to the small barbed fitting and the small hose to the large barbed fitting on the gen set. The unit primed right up and ran like a champ. After a couple of minutes I decided to turn on an AC unit to see how the gen operated under a load. As I walked to the side of my trailer I noticed gasoline spraying out on the ground at the rear of my trailer. I immediately turned the gen off. Long story short, no one at the dealership had ever had any experience with an EFI generator set. When the liquid fuel from the return side of generator went in the fuel vapor line it filled the carbon canister with gasoline and it then came spilling out the vent line. That being said, if you buy and EFI generator be prepared to run an additional liquid return line to your on board fuel tank. My gen set does not have a vapor return line. Vengeance/Forest River factory offered no help. The dealer is going to replace my carbon canister since their techs told me to switch the fuel lines around. I will be dropping my on board fuel tank and adding a return liquid fuel line myself. Hopefully the manufacturers will start offering units prepped for EFI generators since they are the wave of the future.

[oldblueroadking]

Thank you for your information. I have purchased an EFI Cummins Onan as well, have the 2 hoses as well as the wiring harness in the generator compartment. I'm wondering how your additional fuel return line install went. Was there a place in the fuel tank for the hose to be hooked up to? I'm guessing the wiring is right for the EFI just need to run the extra fuel return line. Any advice would be appreciated

[Toddyman88]

In the middle of this now.
Anything new???
Your install working ok?
Very curious to know.
Thanks

[smitty31093]

I replied to you on private message. Did you get it? The return hose can be connected to the fuel tank where the overflow fuel line plugs into the tank. I blocked off this line coming from the fuel filler and used that nipple for my return line. Works great for me. There is a second fuel line running from the fuel tank to the carbon canister so any vapors are still captured.