My Onan with 2k hours on it has started giving me fits.
The problem started in the driveway, with a full tank of fuel. It would start, run and then stop. This was 2 days before I left for a 1 month trip where I needed the gennie alot.
Checking the float boat drain, it was empty, so I guessed bad fuel pump. However no one in town had one, and I could not find any way to get one quickly enough so I made due with a universal fuel pump from Autozone.
This one if anyone is in a pinch, it seems to be in stock most every autozone I stopped at. Its Chinese and not a direct fit, but easy to adapt.
I also put a new fuel filter in, as I had one in stock already just incase. I also added a fuel pressure gauge between the pump and the carb so I could see what was going on. FP with this pump was in the 7psi range.
After that, the generator started and ran fine for 2 hours in the driveway, so I assumed I had fixed it.
Two days later, on the trip, after running for a few hours the generator stopped. I never got below a 1/2 tank of fuel. When I got to the campground I checked the float bowl, and it was again dry, maybe 3 drops of fuel.
Assumed a bad Chinese pump. Went Autozone and got a second pump. I also went to NAPA and got a facet posi-flo ( https://www.napaonline.com/en/p/BK_6101050
). I wired the two pumps in line with the posi-flo closest to the carb, and I used a 2 position switch to pick witch pump to use. Tested in the campground and everything seemed fine. on either pump.
Next day on the road, again the generator dies after an hour or so, swtich to the second pump and it dies soon after, both with a 36 and dry float bowl. I am starting to think that perhaps I have a bad logic board that is killing the fuel pump power due to a defect. So at the next campground I let the fuel pump run free for an hour and it pumps without issue 5 gallons of fuel back into a gas can.
Thinking if the logic only gets hot when the gennie is hot, I decide to hotwire the fuel pump to 12v power. I start the gen normally and after its running I hook the hot side directly to 12v power. In the RV I keep a AC fan running so I know if the gennie dies so I don't have a huge fire risk.
Driving down the road for 4 hours no issues then the gennie dies. 36. I stop and unhook the hot power. I don't check the float bowl because I know the pump has refilled it (I can tell from the pressure on my fp gauge). Now I am confuzzled.
So its not the logic board. Maybe its the fuel pickup? I fill the tank (still way above half) and prime and start the generator. It runs the rest of the day (5 hours). I am now thinking maybe its the pickup or something. To be sure I order an airtex direct replacement and a few new filters from amazon to be delivered to my destination a few days away.
Long story longer. I change to the airtex fuel pump and remove all changes that I have made. The generator may run for 1 hour, or 6 hours or any amount of time and it still dies with a 36. Often when it dies, it is very difficult to prime again (again, I watch the fuel pressure gauge and I can see when the fuel is getting pumped). It seems to die at any level of fuel. And yet I have had it run all the way down below 1/4.
Not sure what it could be. I even though vapor lock, but when it doesn't run I don't notice an inrush of air when I open the fuel fill.