Onan Marquis 5500 Genset-year 2000
- Thread starter mudshark
- Start date
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nfredrick
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- Mar 13, 2017
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on Marquis: Oil level switch located at base of oil filter , take off sheet metal panel around oil filter to gain access
Hi All
OK, my water leak is fixed and the washer/dryer is back in operation. Now it is back to the generator problem. I got the sheet metal cover off and I disconnected the oil sensor. Still no run. It starts right up like it wants to run but, release the switch and it stalls. Where do I go next?
On a side, how in the world do they change the back spark plug? This is an opposed flat two cylinder stuffed into a spot that is barely big enough for it. I can't even see the back plug lead let alone change it! Do they pull the unit for service??
OK, my water leak is fixed and the washer/dryer is back in operation. Now it is back to the generator problem. I got the sheet metal cover off and I disconnected the oil sensor. Still no run. It starts right up like it wants to run but, release the switch and it stalls. Where do I go next?
On a side, how in the world do they change the back spark plug? This is an opposed flat two cylinder stuffed into a spot that is barely big enough for it. I can't even see the back plug lead let alone change it! Do they pull the unit for service??
An update:
I disconnected the fuel filter at the carb, cranked the engine and plenty of gas came out. Therefore, the fuel pump and fuel filter are OK.
Then I took the cover off the control box. Nothing looks burnt or damaged in there. What's next?
I disconnected the fuel filter at the carb, cranked the engine and plenty of gas came out. Therefore, the fuel pump and fuel filter are OK.
Then I took the cover off the control box. Nothing looks burnt or damaged in there. What's next?
Even though you unhooked low oil sensor, might make sure wire is not grounded somewhere or end of wire not touching something. Might run a continuity test between end of wire and engine block. Sensor works by sending ground to control box when oil is low. I?ve never owned a Onan that senses temperature, but if your does, I?d check that sensor the same way as low oil sensor and wire.
nfredrick
Well-known member
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- Mar 13, 2017
- Posts
- 58
Some models require that the oil pressure switch be grounded to keep running
go here and download the Onan troubleshooting guides
https://www.flightsystems.com/troubleshooting/
Check the oil pressure switch as soon as the engine starts. Models showing ?LOP to GND? under CONDITIONS
REQUIRED TO KEEP RUNNING need the oil pressure switch to be closed to ground when
running. If the voltage on the LOL/LOP SW pin of the control does not go to near zero, the switch is not
closing. These switches sometimes stick open if the generator has not been used or exercised often enough.
Multiple start/stop cycles and/or tapping on the oil pressure switch will sometimes fix it. It may be necessary
to temporarily jumper the switch to ground to keep the engine running. This can be done at the switch
or at the OIL LOL/LOP SW pin on the control board.
Models showing ?LOP Open? under CONDITIONS
REQUIRED TO KEEP RUNNING have electronic governors and require the low oil pressure switch to be
closed at starting but open during running. When the switch opens, the governor module places a ground on
the oil pressure input of the control board (P1-5). It is OK to temporarily ground P1-5 on this model to keep
the engine running. N
go here and download the Onan troubleshooting guides
https://www.flightsystems.com/troubleshooting/
Check the oil pressure switch as soon as the engine starts. Models showing ?LOP to GND? under CONDITIONS
REQUIRED TO KEEP RUNNING need the oil pressure switch to be closed to ground when
running. If the voltage on the LOL/LOP SW pin of the control does not go to near zero, the switch is not
closing. These switches sometimes stick open if the generator has not been used or exercised often enough.
Multiple start/stop cycles and/or tapping on the oil pressure switch will sometimes fix it. It may be necessary
to temporarily jumper the switch to ground to keep the engine running. This can be done at the switch
or at the OIL LOL/LOP SW pin on the control board.
Models showing ?LOP Open? under CONDITIONS
REQUIRED TO KEEP RUNNING have electronic governors and require the low oil pressure switch to be
closed at starting but open during running. When the switch opens, the governor module places a ground on
the oil pressure input of the control board (P1-5). It is OK to temporarily ground P1-5 on this model to keep
the engine running. N
Gary RV_Wizard
Site Team
The short version of nfredrick's reply is that disconnecting the sensor may simply prevent it from signalling "pressure OK", thus guaranteeing a shutdown.
Modern oil pressure sensors generally work by giving a continuous positive indication of adequate pressure. If that signal is not received, the controller shuts the engine down. Onan changed oil sensor types around 2000-2001 and I don't know which type you have.
You will want an Onan Marquis service manual to tell you how to test your particular sensor.
http://www.cleggind.com/postal_tech/pdfs/onan_srv_man_pt1.pdf
http://www.cleggind.com/postal_tech/pdfs/onan_srv_man_part2.pdf
Modern oil pressure sensors generally work by giving a continuous positive indication of adequate pressure. If that signal is not received, the controller shuts the engine down. Onan changed oil sensor types around 2000-2001 and I don't know which type you have.
You will want an Onan Marquis service manual to tell you how to test your particular sensor.
http://www.cleggind.com/postal_tech/pdfs/onan_srv_man_pt1.pdf
http://www.cleggind.com/postal_tech/pdfs/onan_srv_man_part2.pdf
Thanks guys
I am going to try a trick that my dad used and other have suggested, to whack the carb bowl and the oil sensor with the handle end of a screw driver. Sometimes that will loosen things up. I also want to get my meter and see what readings I get from the oil sensor and its pigtail. Will post soon.
I am going to try a trick that my dad used and other have suggested, to whack the carb bowl and the oil sensor with the handle end of a screw driver. Sometimes that will loosen things up. I also want to get my meter and see what readings I get from the oil sensor and its pigtail. Will post soon.
OK, I went out and checked things.
Putting my meter in the pigtail on the oil sensor gave me a reading of 1.5 on the 200K range. It did not change when I rapped it with the end of a screwdriver. The oil sensor read 0 so I assume it doesn't pass anything when the generator is off. Rapping the carb did nothing. Genny still won't stay running.
Putting my meter in the pigtail on the oil sensor gave me a reading of 1.5 on the 200K range. It did not change when I rapped it with the end of a screwdriver. The oil sensor read 0 so I assume it doesn't pass anything when the generator is off. Rapping the carb did nothing. Genny still won't stay running.
Lou Schneider
Site Team
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- Mar 14, 2005
- Posts
- 13,275
mudshark said:
Actually, it's the other way around. When you're on a Resistance range zero indicates continuity, which means the sensor is providing a path to ground. The question is does the sensor change state (reads OL or infinity) when the oil pressure comes up.
If it reads the same while the engine is running, the sensor is defective or you have an oil pressure problem.
The other thing the control board needs to see is voltage from the generator. Can you measure that while you hold down the Start switch so the engine stays running long enough to make the test?
Gary RV_Wizard
Site Team
Remember the oil sensor is NOT operating a gauge, so it doesn't differentiate pressure levels. There are only two meaningful pressures, OK and Not OK, so it's basically a pressure-operated switch. When the pressure increases enough to overcome the internal mechanical resistance designed into the switch, it opens or closes per the design. In this case, your measurements suggest that the controller sees either zero resistance (short to ground) or a resistance of 1.5.
The fact that you see a state change in the oil pressure switch suggests it is working as designed.
The fact that you see a state change in the oil pressure switch suggests it is working as designed.
nfredrick
Well-known member
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- Mar 13, 2017
- Posts
- 58
I would still try running it with the oil sender disconnected , if that doesn't do it try grounding the pigtail
2PawsRiver
Well-known member
Have determined you are a saint and the most patient man ever......my post would have already read.....pulled generator, cussed it, hoped it felt pain while I beat it with a sledge hammer, lit it on fire...??.bought new generator.
Hope you figure it out soon, looking forward to hearing fix......cudo's to all those with knowledge and care enough to try and help.
Hope you figure it out soon, looking forward to hearing fix......cudo's to all those with knowledge and care enough to try and help.
Sorry, my last post was in error. I thought about it last night.
Checking the oil sensor I should have said I got no reading when I checked the spade to block suggesting the switch is open. I will try grounding the oil sensor pigtail and see if it runs. I don't have any jumpers with me so I am not sure how I am going to do it.
2PawsRiver
I am not that patient and I am certainly no saint! But I am cheap. I don't want to spend $5k on a new genny.
Checking the oil sensor I should have said I got no reading when I checked the spade to block suggesting the switch is open. I will try grounding the oil sensor pigtail and see if it runs. I don't have any jumpers with me so I am not sure how I am going to do it.
2PawsRiver
I am not that patient and I am certainly no saint! But I am cheap. I don't want to spend $5k on a new genny.
Gary RV_Wizard
Site Team
No need to even consider a new genset. Even a new stator is a lot less than $5k.
Hi Gary
That may be true but what will the labor cost?
I jumped out the oil sensor, no luck. I killed the power to the entire coach and took all the connections at the generator apart. Every thing looks good and clean. I give up. I will have to see if I can get a tech out here.
That may be true but what will the labor cost?
I jumped out the oil sensor, no luck. I killed the power to the entire coach and took all the connections at the generator apart. Every thing looks good and clean. I give up. I will have to see if I can get a tech out here.
Gizmo100
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- Sep 28, 2018
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- 3,065
mudshark said:
Why the carb??...I think I missed something. ???
