Onan problems

I had the same problem with shutdowns on my Onan 4000 and the problem was the coil, about $60.
The tough part is pulling the unit out of the motorhome and then apart a little to get to the coil. My motorhome is a 2003.

j-d wrote:
Onan wants us to use a pump that serves as a positive fuel line shutoff when NOT running. Some models had a Pump that was NOT shutoff and there was an extra solenoid valve to accomplish this. Here at Facet-Purolator the specs on LOW pressure pumps include whether they are shutoff or not. I replaced an old Facet type solenoid pump with a little aftermarket one (labeled only "Purolator" back then). It worked fine and never caused a problem by NOT being shut-off. The risk would be that the coach's fuel system would pressurize the genset's carburetor and the Float Valve wouldn't hold, letting it flood over.
All that said, Amazon offers pumps that are a direct match to many Onan applications, reasonable price and no need to improvise. They actually looked less expensive than improvise, HERE.
Yeah, Where's the Fun in That?

The caution I would give with fuel pumps is to make sure the flow rate is at least and close to original and the psi is within 2-3 psi.

I have a post somewhere I recently updated with a pump I just used on an Onan, with the specs.

Onan wants us to use a pump that serves as a positive fuel line shutoff when NOT running. Some models had a Pump that was NOT shutoff and there was an extra solenoid valve to accomplish this. Here at Facet-Purolator the specs on LOW pressure pumps include whether they are shutoff or not. I replaced an old Facet type solenoid pump with a little aftermarket one (labeled only "Purolator" back then). It worked fine and never caused a problem by NOT being shut-off. The risk would be that the coach's fuel system would pressurize the genset's carburetor and the Float Valve wouldn't hold, letting it flood over.
All that said, Amazon offers pumps that are a direct match to many Onan applications, reasonable price and no need to improvise. They actually looked less expensive than improvise, HERE.
Yeah, Where's the Fun in That?

A bit of info about the normal operation of an Onan fuel pump might be of some value to anyone interested in the topic.

I had the opportunity to tear one apart that came out of a Onan 5500. The fuel pump consists of a solenoid that is activated with 12 Volt pulses that in turn cock a spring and the spring provides the fuel pressure (a spring loaded solenoid that acts like a piston pushing the gas through a check valve). There is no feed back loop to the pulses, they just come a couple every second or so and cock the spring whether it needs cocking or not. That is what makes the noise which can be heard when pushing the priming switch. As far as I could determine the O rings around the solenoid (piston) were not up to maintaining the fuel pressure. So the worse the O ring the more noise because of the longer strokes.

I was able to successfully replace the Onan pump with a 3rd party pump from an auto parts store. They too work on the basis of a spring driven piston (solenoid) through a check valve.

Does your Onan have a low oil sensor? A faulty sensor sometimes cause a generator to quit when it gets hot.

DiskDoctr wrote:
I've seen Onan control board defect and not output enough volts to fuel pump. About $150 a few years back for a new board.

Solution? If the voltage is more than about 0.5 volts below your battery voltage, simply install a relay in this (+) line to the fuel pump and install a new fuel pump (possibly the fuel pump failure damaged the circuit board?).

The relay will allow you to run a new (+) wire from the battery though the relay to the new fuel pump.

You could try connecting a DVM to the (+) side of the fuel pump and watch it carefully. If it is too low or drops...simple fix.

Yikes, Onan control board was $800+ a few years ago.

I've seen Onan control board defect and not output enough volts to fuel pump. About $150 a few years back for a new board.

Solution? If the voltage is more than about 0.5 volts below your battery voltage, simply install a relay in this (+) line to the fuel pump and install a new fuel pump (possibly the fuel pump failure damaged the circuit board?).

The relay will allow you to run a new (+) wire from the battery though the relay to the new fuel pump.

You could try connecting a DVM to the (+) side of the fuel pump and watch it carefully. If it is too low or drops...simple fix.

Sounds similar to a problem we had. Stalling after a few minutes is likely fuel or control related, according to what we were told. In our case it was the system board.

Noisy fuel pumps seem to be common, we had a noisy pump replaced under warranty, the new pump ended up making more noise than the original but worked fine!

That sounds like what mine was doing. I still had warranty and they replaced the fuel pump and fuel filter. All has been fine for a month or so but have only used it 2 times. Hope you find the answer in case mine goes again.

Dunno about the 4000, but the Microlite 2800 is a similar design. Mine has gone out twice with similar symptoms. Runs fine for 15 minutes, quit. Run fine for an hour, quit. Once it was the fuel pump, the second time it was the voltage regulator. Both times were in hot weather.

I found trouble shooting guides in the Onan service manual, and online at the Flight Systems website. You'll need a VOM (aka multimeter), not much else.

The 2800's voltage regulator is easy to find, but a beast to replace. 1 multiplug, 1 Torx screw. But the screw & hole are invisible under the engine, and there's no locating tab or lead-in to the hole. It's a serious pain but possible to do thru the access door on the 2800, not sure on the 4000. IIRC, the 2800's VR cost about $225 or so from Flight Systems.

Jim, "Mo' coffee!"