Forum Discussion

zonearc's avatar
zonearc
Explorer
Mar 31, 2014

Onan 4000 Generator Won't Start

New (old) RV. Working through the various quirks.

When you try to start it, it usually doesn't do much. Every so often tries to kick over for a second. Has a fuel filter (clear) near the electric fuel pump and I noticed that when I kick it over, no fuel is moving through it at all. However, you can hear the fuel filter clicking away. To me, it sounds like the fuel filter is toast because it should be chugging fuel through the filter, right?

Below is the unit I have:

http://i.imgur.com/gmx3VHX.jpg

I noticed it uses hard lines, which seems it would make it more difficult to use the various generic fuel pumps I've used in rigs before? Is there some sort of adapter I could drop in at the end of the hard line so I could use pumpers tape, and rubber hoses and splice in a new generic one?

Thanks =)
  • One way to rule out the fuel pump is to run the outlet line to a bucket and see if when you try to start the generator if it pumps gasoline into the bucket.

    This is a somewhat dangerous test as you will be cranking a motor with open gasoline nearby so have a fire extinguisher and the garden hose on and close at hand.

    But you should know within a couple of seconds whether or not your pump is pumping gas.

    I don't know what you mean about the "fuel filter ticking away". The fuel filter should not make any noise. Perhaps you meant you can hear the pump ticking away?

    Checking the filter is easy - remove it and blow through it. If you can blow through it, it's fine. Be careful and don't suck gas down your lungs, obviously.

    Check the oil. These generators have an oil pressure sending unit and will shut down the generator if they don't detect oil pressure. You can disconnect or short out (I don't remember which) the sending unit to figure out whether it is the sending unit or not. You'll have to google on that.

    These generators also have internal electronics that will shut down the generator or not allow it to run if it is not operating within certain parameters. Newer generators have a diagnostic display but not ones as old as yours (and mine).

    You can try choking it to get it to run by putting your thumb partially over the air intake. If you can get it to run that way you've got a carb blockage.
  • j-d's avatar
    j-d
    Explorer II
    Back to your question, if:

    There is fuel
    There are not vacuum leaks in line from tank
    Filter is clear
    Pump is working

    Then the pump would have filled the carburetor and you wouldn't see much fuel moving in a clear filter or a clear fuel line.

    A good test would be to connect pump output to a line you can safely direct into a can where you can see what's coming out. Then power the pump with a 12VDC jumper. It should then pump steadily and move fuel in a steady unrestricted flow.

    Please send us the Model Model and SPEC Code of the ONAN
  • j-d's avatar
    j-d
    Explorer II
    Pic of his pump:



    That's about a $40 part. But what it fueling? Is this "tank" part of the RV, part of the generator, a separate tank?

    Can you furnish Make Model, Spec if ONAN, Year of genset?

    Back to the Pump, here's a Link to Facet-Purolator

    Yours looks like a Cube Electronic. Genset probably wants a low pressure 3-5 PSI model vs the higher 5-7 PSI and at least ONAN likes one that won't allow fuel to flow through it when it isn't running. The F-P site calls that feature PSO (Positive Shut Off, and also Anti-Siphon).

    Be careful if you get this thing running. I'm pretty sure it's a constant-RPPM generator. This means that it runs at a steady RPM (and I'm guessing 1800) whether no load or full load. Only difference is throttle opening. THIS MEANS that if you goose it up by grabbing the throttle linkage, the voltage will go way above the 120 it's meant to deliver. Pretty much anything connected and ON will be damaged.
  • Shouldn't I see fuel flowing through the fuel filter to the point where the clear sectionhas no air bubbles if its working? If it's not moving any fuel l, shouldn't I start with a new pump? Also, this is a 87 RV, I don't know how old the generator is.. I doubt it's covered under warranty =)
  • If the generator has been sitting for awhile and not started at least once a month, then likely the carburetor is plugged up and will need to be replaced. They are so small (compared to a car) that even a little bit of varnish will totally plug the jet. When sitting for any length of time (like winter) they need stabil or a similar product in gas and should be started monthly.

    There have been some problems lately with Onan 4000s with the fuel pump. But usually the symptom has been fuel leaks. Onan has been replacing them under warranty. Get the serial number off the unit and check with them.
  • Not sure, but I just filled the tank on the way home from picking it up so shouldn't be that?
  • Does your rig have a fuel level limit in the tank for the generator? Mine won't allow generator when the tank is less than a quarter full.
  • http://images02.olx-st.com/ui/1/52/45/4194745_1.jpg

    That's a picture I found on the internet of the exact model I have. Where is the intake? I've rebuilt a few carbs in Toyota's and Ford's in the past, but I've never worked on a Generator. I'm use to spraying start fluid down the noise of a 2-4 barrel carb so this looks a bit foreign =)
  • does it start for a bit if you use starter fluid in the intake? If so, its probably the pump.