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03 Onan 7KW Marquis in Motorhome


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  #1  
Old 09-08-2017, 11:23:26 AM
Cruiser Cruiser is offline
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Default 03 Onan 7KW Marquis in Motorhome

My genset will run until it gets hot outside, 90F +. Then it shuts off and will restart Then starts searching and quits again. Oil is full and cleaned air return on bottom of unit. Any ideas would be appreciated!
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  #2  
Old 09-08-2017, 12:47:08 PM
len k len k is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

Need full model and serial number to know what you have, onan made a lot of gens.

"Starts searching" ........ do you mean rpm is hunting?........ rpm bouncing around with a no change in electrical load.

Is 120 V voltage output constant ?
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Old 09-08-2017, 01:19:21 PM
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Default Re: 03 Onan 7KW Marquis in Motorhome

Model# 7HGJAB-900B Serial# K020441355

---------- Post added at 01:19:21 PM ---------- Previous post was at 01:14:50 PM ----------

The RPMs of unit will actually start to slow down. Then before it shuts down it will start almost acting like it's starving for fuel.
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Old 09-08-2017, 03:33:05 PM
len k len k is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

spec B, Made Nov of 2002

With steady electrical load, when it's losing rpm check throttle position. If it's ~ WOT then it's likely starving for fuel. Fuel supply problem.

If squirting a little stream of gasoline down carb throat brings rpm back up it is a fuel supply problem.

Good to not let it shut down with large load on it, AC voltage regs don't like that. Stresses them, can die eventually

Also check that hot exhaust cooling air is not being sucked back into cooling air intake. Might need some sheet metal between the 2 openings to prevent that.

Last edited by len k; 09-08-2017 at 05:13:55 PM.
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Old 09-08-2017, 06:40:43 PM
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Default Re: 03 Onan 7KW Marquis in Motorhome

Was gonna change oil plug and fuel filters. Figuring it might be a over temp sensor
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Old 09-08-2017, 06:46:34 PM
len k len k is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

I don't see an eternal temp sensor in schematic at back of service manual for HGJAB.
Could be one internal to control board though, but pervious models like 6.5 NHE, 7NHM didn't have temp shut down.
But would guess it would display a fault code if shut down on over temp. Flashing LED.
I gave a very breif skim of trouble codes in back of service manual, didn't see code dedicated to only over temp.

Manual number and link to them.
HGJAA HGJAB HGJAC HGJAD HGJAE HGJAF ----SERVICE---- (01-06)--- 983-0501D.pdf <--read this one
HGJAA HGJAB HGJAC -vert shaft (sepc A-C))--- PARTS--983-0201D.pdf
http://www.twinslan.net/~n0nas/manuals/onan/

Link has been down for past few days , server issues. might be up tonight. Info on that here
https://www.smokstak.com/forum/showthread.php?t=155507

Last edited by len k; 09-08-2017 at 08:19:03 PM.
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Old 09-08-2017, 11:19:41 PM
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Default Re: 03 Onan 7KW Marquis in Motorhome

I'm thinking maybe vapor locking or fuel pump is loosing pressure when gets hot? Tuning it up tomorrow with plug oil fuel filters. Would 91 Octane be better to run in the hot weather.
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Old 09-09-2017, 09:03:37 AM
Oldchvys Oldchvys is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

If you are thinking it might be vapor lock, a quick way to check is to disconnect the fuel supply from the coach and run the genset from a gas can. From the way you described it, it does sound like a fuel pump problem though.
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Old 09-09-2017, 10:10:05 AM
len k len k is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

I've no experience with vapor lock.

If RV is stationary as a test might even get a sheet of plywood or something between hot cooling air exhaust and cooling intake, to prevent recirculating hot air into intake. Make sure it doesn't touch or is too near anything hot that may make it catch fire.
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Old 09-10-2017, 01:00:10 AM
Doug Reed Doug Reed is offline
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Default Re: 03 Onan 7KW Marquis in Motorhome

TwinsLAN is still down. I have many of the files on Google Drive and will copy the rest when TwinsLAN comes back. Use this link for Google Drive. I did see both of your files there.

https://drive.google.com/drive/folde...28?usp=sharing
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Old 09-10-2017, 09:05:00 PM
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Default Re: 03 Onan 7KW Marquis in Motorhome

Just a update, Did a quick tune up plugs, fuel filters and oil change.Added some Octane boost to help with possible vapor lock. Yesterday ran it for 2 plus hrs with both A/C units on, 94F Ambient. All good. Today started it ran for just about 2 hrs 104 F ambient with both A/C running shut down. Will try to draw out of a fuel can and possibly replace the fuel pump. Airways all seem overwhelming be clear.
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Old 09-10-2017, 09:23:10 PM
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Default Re: 03 Onan 7KW Marquis in Motorhome

're-read post #9. Clear helps but be sure that intake is not pulling in hot discharge air.
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