Onan 5.5 EFI Genset Installation

smitty31093 · 06-19-2016, 08:12 PM

I just bought a new Onan 5.5 EFI generator to install in my generator ready Vengeance 320A. I thought this would be a simple plug and play install since the TH is supposed to be Onan ready. The TH has a wiring harness with a plug containing 5 wires. The genset has a wiring harness with 5 wires but no matching plug. The wires are not the same colors as the ones in the TH. I need to get the other half of this plug and figure out which wires match the corresponding wires in the trailer plug. I have an onboard refueling station and the fuel lines are curled up in the battery compartment of the TH. They are two different sizes so it will be easy to figure out which goes on the supply side of the generator and which goes to the return. I will have to get an exhaust pipe flange and tail pipe from Onan. There must be a wiring diagram somewhere for the TH and the generator. Any advice much appreciated.

spaach · 06-22-2016, 10:48 PM

The wires you see from the Gen set are the 2 120vac circuits. Green is ground, the 2 whites are neutral, black is l1, and black/yellow is l2. The plug you have has a matching connection inside the Gen set on a pigtail by the control board.

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smitty31093 · 07-26-2016, 03:27 PM

I finally got my Onan Cummings 5.5 EFI generator installed. The hardest part was picking it up and sliding it into the belly of the 5th wheel. Since this is an electronic fuel injected unit I had to have a remote electric fuel pump. I hooked everything up and tried to start. Long story short; when i put the fuel suction hose into a 5 gallon gas can the unit primes easily and runs great. When I plug into the fuel line going to my onboard refueling station the generator will not prime and will not run. My onboard tank has almost a half tank of gas. It appears the suction hose to my onbard fuel tank is not low enough in the tank to draw gasoline. There are no kinks in the hose and there doesn't appear to be any damage. How do you get to the tank to inspect the pickup for the fuel line?

BBQGUY · 07-26-2016, 03:56 PM

Could be several issues.
Verify you are using the large diameter line as the EVAP line. The smaller is the fuel line.
Test the rear fuel pump: Connect a short line to the discharge of the fuel pump, do you get fuel when you turn the pump on?
If No; loosen the fuel cap to the tank and try again.
If No again, disconnect the fuel line from the input side of the rear pump and blow air in the line to the tank. You should hear the air enter the tank. If no report back.

No:

smitty31093 · 07-26-2016, 09:56 PM

[QUOTE=BBQGUY;1271530]Could be several issues.
Verify you are using the large diameter line as the EVAP line. The smaller is the fuel line.
Test the rear fuel pump: Connect a short line to the discharge of the fuel pump, do you get fuel when you turn the pump on?
If No; loosen the fuel cap to the tank and try again.
If No again, disconnect the fuel line from the input side of the rear pump and blow air in the line to the tank. You should hear the air enter the tank. If no report back.

Thanks BBQGUY! The Gen set has the 5/16 fuel barb labeled feed line and the 1/4 " barb labeled return line. Since my TH is prewired and plumbed for an Onan Cummngs Gen set I automatically plugged the larger hose to the feed line and the smaller to the return. As stated, I couldn't get the Gen set to prime with this configuration. After consulting with the tech at the dealership I decided to switch the hoses. The Gen set immediately primed and the unit cranked right up. The problem now is the return line to the tank is apparently plumbed wrong because gasoline is pouring out of what looks like a 3/4" vent hose. The vent hose comes out of a separate small tank that is beside the actual fuel tank. I can't find a blueprint or a drawing of the refueling station and Gen set tank and lines anywhere on line. Without a drawing to go by I don't know if the fuel lines are plumbed correctly or not. Suggestions greatly appreciated. I would really like to figure this out on my own so I don't have to do without my camper for weeks while it sits in line at the dealer waiting to be worked on, even though it is brand new and under factory warranty.
BTW, I don't think I have a rear fuel pump, except for the pump that is used for my refueling nozzle.

BBQGUY · 07-27-2016, 08:35 AM

Do you have the installation manual? If not download it from here.
https://www.norwall.com/product_pdfs...stall_2015.pdf
Fuel connections starts on page 30.

You have a problem.
The EVAP line (5/16") is not the fuel return line and the small tank is not a tank but a vapor canister. The canister has to be replaced and the EVAP line purged. Get the part number off the canister to replace it. See figure 15 on page 31 of the manual for the location of the EVAP connector on the genset. The EVAP line is item (7).

You are missing the return fuel line.
Your trailer was not prep'd for the EFI genset which requires 3 fuel lines: Supply, Return, and EVAP. You will have to run the 1/4" return fuel line to the tank. See Figure 15 on page 31 of the manual. This line is item (9).

It appears you have a remote fuel pump installed.

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