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Old 11-29-2021, 06:17 PM   #1
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Onan Generator IssuesÖ..

Good evening everyone. This post might be a bit lengthy, so please bear with me, as Iím hopefully going to get some help/suggestions from someone here.

So here goes. My wife and I bought a new to us living quarters horse trailer (2015 Model) with a on-board Onan Generator. The day before we left
To lick it up, the owners messaged me and said they were unable to get the generator to run. But according them them it ran last time they used it.

Itís a Onan Marquis 5000 if I remember correctly.

Model # 5BGMFA26105G
Serial # H963573857.

I just looked at the data plate and says itís a 5kw

I downloaded the service manual, and started going through it.

So when I got the trailer home, I got on top
Of the trailer and opened the generator doghouse, only to find the top and side shields were missing off it, and it appeared this generator was a lot older than a 2015. I immediately messaged the previous owner, and she said they had removed it from their older horse trailer when they ordered this one, and just ordered the new one with a generator prep package so they could install this one. Ok, makes sense.

So I first tried starting it and it would crank and crank and crank, no fire. Found the fuse that controls the fuel pump blown, due to a wire being pinched between the case. Fixed all that, new fuse and bam, it fired, but wouldnít stay running.

I have since replaced. Plugs, wires, brushes, brush springs, cleaned the slip rings, new low oil switch, new coil. And still, will fire and runn5-10 seconds then die. I have a new fuel filter that mounts to the carb, new fuel pump at the unit, and a new fuel pump down below at the fuel tank (to pump fuel from down below up to the pump at the generator. I have all these parts on order, but havenít arrived.

I am so stumped at what to do next, but a new equivalent generator is $4500 so I can afford a few parts to try and get this one going. I donít know whether itís a fuel issue, ignition module, etc. just extremely stumped so far and maybe any help you all could provide would be much appreciated!

Also fyi, the fuel tank is at 3/4, so I know it has plenty of fuel.
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Old 11-29-2021, 06:22 PM   #2
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You talk about a live aboard horse trailer with a built in generator. You also speak of the fuel tank being more than 3/4 full. I don't understand. Do you have a gasoline tank on your horse trailer? All I know of have propane fueled generators.

David
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Old 11-29-2021, 06:26 PM   #3
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Does your service manual show you how to read the error code? That is what I would do next. Hopefully, that will narrow down the possibilities. Will the generator run as long as you hold down the start button?
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Old 11-29-2021, 06:48 PM   #4
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Can you post a picture of the gen and carb.. and gas tank.. ? I am concerned that the shields are missing ?
It really sounds like the lower pump is not doing it's job.. but your close.. I also feel you need to adjust main jet...
If gen has been setting for a long time.. it might be time to clean the carb..
I would 1st adjust.. then get can of carb cleaner... disconnect fuel line at carb..
Then use straw with tight rag and force cleaner into carb bowl.. through the fuel inlet.. let set 4hrs or so..
While waiting on that.. remove air cleaner and housing.. you want to spray cleaner in throat of carb.. now use strong flashlights.. aim directly at the 1 or 2 holes at the top of throat and the aim at the big one in the bottom of carb.. that is main jet..
Let cleaner work.. then try.. only works 80% of time.. but no taking carb apart..
Make sure choke is working.. check that choke pull off vacuum line is not leaking..
Now.. critters find old rv tasty wires and rubber hoses and lines on rv and eat the tiniest holes that will leak air into fuel line.. so replace all fuel line.. just the tiniest cracks in the line and pump looses prime..
When things go haywire and don't make sense keep critters in the back of your mind all the time..
Make sure there is no nest between gen head and eng.. there is a space between the 2 and critters love to nest there.. I blow it out with hi pressure air and see..
You might have to remove the black box looking ignition module is usually mounted on top of eng.. look down make sure it's clear.. look for the 2 magnets that trigger the module.. they are on 2 plastic figures..
Good luck and let us know what you did and maybe better members then me will help you
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Old 11-29-2021, 07:14 PM   #5
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This might help: https://www.flightsystems.com/pdf/on...ting-guide.pdf

First make sure all the connectors and control wires are good.
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Old 11-29-2021, 07:34 PM   #6
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Quote:
Originally Posted by DavidEM View Post
You talk about a live aboard horse trailer with a built in generator. You also speak of the fuel tank being more than 3/4 full. I don't understand. Do you have a gasoline tank on your horse trailer? All I know of have propane fueled generators.

David
David, yes, it has a onboard generator with a separate gas tank specifically for the generator. The front of the trailer has living quarters on it, and this is what the generator is for is to power the 120v portion of the living quarters in the event we are somewhere that doesnít have full hookups.
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Old 11-29-2021, 07:35 PM   #7
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Originally Posted by PJStough View Post
Does your service manual show you how to read the error code? That is what I would do next. Hopefully, that will narrow down the possibilities. Will the generator run as long as you hold down the start button?
This generator is old enough it does not have a way to produce or read error codes like the newer Onans do.
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Old 11-29-2021, 08:05 PM   #8
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Originally Posted by ksstang View Post
This generator is old enough it does not have a way to produce or read error codes like the newer Onans do.
Just so you know, there are after market parts for things like voltage regulators at half the OEM cost.

I have 3 generators, an 800 watt one that I got when my first Onan was new to me. When my current 6500 watt LP Onan was new to me spent a lot of time getting it to run and make electricity at the same time.

My third is a gasoline 2200 watt inverter generator that will run an A/C. First it cost less than Onan parts. Second, propane was the limiting factor when boondocking.
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Old 11-29-2021, 09:21 PM   #9
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I was reading the manual and see that when the start switch is activated, battery 12VDC is applied to E3 & E4; once the unit starts and generates some volts, there is a bridge rectifier to provide the 12VDC for them.
Could you see if the fuel pump and fuel valve both have 12VDC those first few seconds and after? The fuel fuse is part of that circuit and if there is a problem, may be the reason why it opened.
Can you confirm the Spec. of the unit also? (on the nameplate)


Fuel Pump (E3), Fuel Valve Solenoid (E4)
The E3 fuel pump is initially energized (through
CR9) at the same time the start solenoid K1 is ener-
gized, by closure of start relay K4 contacts. After the
set is started, fuel pump relay K6 is deactivated and
the fuel pump then receives its current through a
separate connection. Fuel pump power is rectified
to DC by CR10. CR9 then serves as a blocking
diode to prevent current flow to start solenoid K1
and fuel pump relay K6.

Fuel valve solenoid E4 parallels fuel pump E3; it
serves as a safety measure by blocking fuel flow
when the fuel pump is not activated.
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Old 11-29-2021, 09:49 PM   #10
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Quote:
Originally Posted by OldWEB View Post
I was reading the manual and see that when the start switch is activated, battery 12VDC is applied to E3 & E4; once the unit starts and generates some volts, there is a bridge rectifier to provide the 12VDC for them.
Could you see if the fuel pump and fuel valve both have 12VDC those first few seconds and after? The fuel fuse is part of that circuit and if there is a problem, may be the reason why it opened.
Can you confirm the Spec. of the unit also? (on the nameplate)


Fuel Pump (E3), Fuel Valve Solenoid (E4)
The E3 fuel pump is initially energized (through
CR9) at the same time the start solenoid K1 is ener-
gized, by closure of start relay K4 contacts. After the
set is started, fuel pump relay K6 is deactivated and
the fuel pump then receives its current through a
separate connection. Fuel pump power is rectified
to DC by CR10. CR9 then serves as a blocking
diode to prevent current flow to start solenoid K1
and fuel pump relay K6.

Fuel valve solenoid E4 parallels fuel pump E3; it
serves as a safety measure by blocking fuel flow
when the fuel pump is not activated.
I have looked all over for the spec on it and so canít find it anywhere. It isnít anywhere on the nameplate.
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Old 11-29-2021, 09:56 PM   #11
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Quote:
Originally Posted by ksstang View Post
I have looked all over for the spec on it and so canít find it anywhere. It isnít anywhere on the nameplate.
HA! I guess reading the manual would help us...
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Old 11-29-2021, 09:57 PM   #12
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Quote:
Originally Posted by OldWEB View Post
I was reading the manual and see that when the start switch is activated, battery 12VDC is applied to E3 & E4; once the unit starts and generates some volts, there is a bridge rectifier to provide the 12VDC for them.
Could you see if the fuel pump and fuel valve both have 12VDC those first few seconds and after? The fuel fuse is part of that circuit and if there is a problem, may be the reason why it opened.
Can you confirm the Spec. of the unit also? (on the nameplate)


Fuel Pump (E3), Fuel Valve Solenoid (E4)
The E3 fuel pump is initially energized (through
CR9) at the same time the start solenoid K1 is ener-
gized, by closure of start relay K4 contacts. After the
set is started, fuel pump relay K6 is deactivated and
the fuel pump then receives its current through a
separate connection. Fuel pump power is rectified
to DC by CR10. CR9 then serves as a blocking
diode to prevent current flow to start solenoid K1
and fuel pump relay K6.

Fuel valve solenoid E4 parallels fuel pump E3; it
serves as a safety measure by blocking fuel flow
when the fuel pump is not activated.
Also, the fuel fuse has not popped since I replaced it. I believe the reason it popped was because the one end of the wire coming out of the fuse holder was pinched between the generator casing and front panel, and was metal on metal. Once I fixed that wire and put a new fuse in it hasnít popped since. I also replaced the one 12v relay, K4 I think it was, I canít remember just to eliminate that as a problem. It shows a second relay just like that one in the schematic, but I canít find it anywhere on the unit to save my life.

The whole thing has me stumped. And really wish I could just afford a new one, but I also donít want to get beat on this one, as Iím typically pretty good at figuring stuff out, but feel like at this point Iím getting my butt whooped. My wife wants me to just give up and haul around our portable oneÖ..but told her that totally defeats the purpose of the onboard one that you can start from inside if itís needed!
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Old 11-29-2021, 10:09 PM   #13
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Quote:
Originally Posted by ksstang View Post
I have looked all over for the spec on it and so can’t find it anywhere. It isn’t anywhere on the nameplate.
So if it is Spec G, then ignore my other post, your unit will use this schematic. It looks like you only have a fuel pump and a choke heater, no fuel valve. So if you could do the voltage check on the pump and choke htr., it will indicate if the loss of voltage to it causes the unit to shutdown.



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Old 11-29-2021, 10:20 PM   #14
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Have you considered doing the control board tests laid out in the manual? A bit of work, but would be a learning experience.
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