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Generator fuel pump fix
Hi fellow RVers,
This post is just an FYI to anyone struggling with poor starting conditions on their Onan Cumins RV 4000 generator. Mine started having start issues to the point that I had to start giving it a shot of starting fluid to get it to start. Once started it ran like a champ. However, turn it off and 10 minutes later no start without starting fluid which meant I had to go outside to start the generator. So after careful diagnostics I figured out that the fuel pump was weak and not able to prime correctly. I attempted to order a new pump from Onan, but they were on national back order. I saw posts about knock off pumps to replace the Onan pump, but by this time I was fairly frustrated with how and where Onan and Winnebago chose locate the fuel pump. If you have done this repair you know what I mean. The pump is located behind the computer module and the started relay making it a pain in the ass to get to and replace. After thinking about it I decided I wasn’t going to participate with this I’ll located pump position and rethought how to fix the problem. I managed to locate a spec sheet on the original Onan fuel pump so I could determine the correct fuel pressure for the system. This is important as to much will override the float bowl and to little will cause lag and stumbling under load. The correct pressure is 3.5psi. So instead of installing a factory pump in the location that takes 2 hours to complete I bought a Holly gas/diesel electric fuel pump from Autozone along with an inline pressure regulator. I mounted the fuel pump to a bracket on the frame that was conveniently located along with the pressure regulator set to 3.5 psi. I put a metal inline fuel filter upstream of the new pump and ran new 1/4” fuel line to the generator carburetor. I extended the two wires to connect with the new pump. The generator now starts perfectly and runs great. The best part is if I have to change the inline fuel filter, pump or pressure regulator it’s a15 minute job. If you ever need to replace the factory fuel pump I recommend this instead of suffering through the hassle of trying to work on it where it is currently located.
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Linear Mode
