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Old 06-21-2014, 10:42 AM   #1
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Diesel generator hard to start

I have an onan 10kw diesel generator in a 2007 holiday rambler 42pbq that will crank over slowly and hesitantly but usually won't start. When I start the coach engine I can start the generator with no problems. Any ideas?
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Old 06-21-2014, 11:09 AM   #2
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Sounds like your gen set starts from your coach batteries, and with the engine running it's getting the voltage it needs to start from the alternator and the chassis batteries. If your coach batteries test out ok for voltage then , you will have to check connections from the batteries to the gen set for poor connections; voltage drop.
If you have the engine off and try starting gen set while using the emergency start / boost switch, will the gen set fire up ?
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Old 06-21-2014, 12:26 PM   #3
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I think Skip426 hit it, what's the voltage on your house batteries? Clean and check all house battery connections and next time try the boost switch so you have an alternative to having to start main engine when house batteries are weak.
A 10kw generator needs a lot of CCA (cold cranking amps) that perhaps your house batteries, which are generally deep cycle, just can't produce, especially if they've been used a bit.
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Old 06-21-2014, 07:40 PM   #4
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And, how old are your batteries? Voltages at batteries?
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Old 06-22-2014, 11:37 AM   #5
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Just wait til you try to start the genny in extreme cold. Unlike the main engine, it does not have a hydro hot pre-heat connection or electrical heater to warm it up before starting. I have to either boost the chasis battery with the house batteries or start the main engine first if the coach has been sitting for a month or when near freezing (or colder). It is just a very long battery cable run from the battery bay to the genny. And as already covered, the 10kw is a pretty big diesel in itself.
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Old 06-22-2014, 08:36 PM   #6
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Thanks for the replies. Doesn't help if I use the boost switch. It does start most times when im plugged into shore power. I will check the voltage but the batteries are only a year old and there are 8 of them. I will also clean all of the connections. Its frustrating as i cant depend on the auto start so i would really like to get this resolved.
Much appreciated folks. If anyone thinks of anything else please let me know.
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Old 06-23-2014, 08:26 AM   #7
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When you sat 8 batteries do you mean 4 house & 2 chassis?
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Old 06-23-2014, 09:48 PM   #8
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Quote:
Originally Posted by Playtime III View Post
Just wait til you try to start the genny in extreme cold. Unlike the main engine, it does not have a hydro hot pre-heat connection or electrical heater to warm it up before starting. I have to either boost the chasis battery with the house batteries or start the main engine first if the coach has been sitting for a month or when near freezing (or colder). It is just a very long battery cable run from the battery bay to the genny. And as already covered, the 10kw is a pretty big diesel in itself.
I am curious about your post. I have not dealt with a 10k but my onan 7500 quiet diesel has glow plugs which preheat the chamber for cold weather starts. When I go to start it the starter does not engage for a preset amount of time to give the glow plugs a chance to heat up. Glow plugs are very standard on diesel engines. My Silverado pickup has glow plugs and my Kubota tractor and my Montana 50 horse diesel has glow plugs. If you are having trouble starting your 10k in cold weather you might want to check to see if it has glow plugs and if they are working. I have started my onan quiet diesel at -6 degrees with no problems.
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Old 06-23-2014, 10:07 PM   #9
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If the 10 kw generator is an Onan Quiet Diesel, it does have automatic timed glow plugs in each of the 3 cylinders. If you're having problems in cold weather, check the glow plugs. When they burn out, it is very hard to start a compression ignition engine. I've had diesel autos for 30 years and when a glow plug or two are bad, it's not hard to tell with when a couple of cylinders don't light off.
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Old 06-24-2014, 10:46 PM   #10
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If the 10 kw generator is an Onan Quiet Diesel, it does have automatic timed glow plugs in each of the 3 cylinders. If you're having problems in cold weather, check the glow plugs. When they burn out, it is very hard to start a compression ignition engine. I've had diesel autos for 30 years and when a glow plug or two are bad, it's not hard to tell with when a couple of cylinders don't light off.
I agree, on my 50 horse tractor which has a Mitsubishi diesel you have to allow the glow plugs time to heat the cylinder. If you try to start without allowing the glow plugs to time out, it will not start. If you allow the glow plugs to time out it starts almost instantly

The difference with my onan quiet diesel you cannot bypass the glow plugs they have to time out before the starter engages.
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Old 06-25-2014, 05:33 AM   #11
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On my 7500 if you hold the switch in the off direction it will pressurize the fuel system before the glow plugs do their job.
Sounds like it could be batteries or glow plugs. It only takes one bad battery to pull down the whole system. I had to replace one of my 4 at 10 months under warranty.
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Old 06-25-2014, 06:34 AM   #12
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Diesel generator hard to start

Quote:
Originally Posted by Dippelj View Post
Thanks for the replies. Doesn't help if I use the boost switch. It does start most times when im plugged into shore power. I will check the voltage but the batteries are only a year old and there are 8 of them. I will also clean all of the connections. Its frustrating as i cant depend on the auto start so i would really like to get this resolved.
Much appreciated folks. If anyone thinks of anything else please let me know.

If you hold down the boost switch for a couple of minutes & then try to start, you should notice an improvement in cranking speed. If you don't, then you may have an issue with your BIRD system which ties the batteries together when one bank or the other is being charged.

As someone mentioned, it's a long cable run up the the generator and the cable may be slightly small for the length of run. There are a couple of connections at the rear of the generator that you should clean up and there is a ground stud that you should also clean up. 12VDC just doesn't have a lot of voltage pressure and it doesn't take much surface corrosion to drop the voltage. 1/2 a volt at the starter can make a real difference.


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Old 06-25-2014, 09:19 PM   #13
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I would check each battery individually. Depending on how they are wired, it only takes one of those new batteries to be bad to cause a bunch of trouble. At least you will know
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Old 06-25-2014, 09:53 PM   #14
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If voltage is O.K., the next thing to check would be the glow plugs. First test would be to hook multimeter set for 12 v DC range and connect black lead to ground and red lead to terminal on the end of a glow plug. When someone hits the generator starter to turn glow plugs on you should read 12 v at the glow plug until the relay times out. If no voltage, relay is bad. If you have 12 v, then you need to switch multimeter to Ohms. Black on ground, red on glow plug end. If you get an infinite reading, the glow plug is bad. If ohm reading is under .5 ohm, it's good. Do this for all glow plugs. They should all be close to the same resistance.
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