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Old 01-12-2020, 12:05 PM   #1
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Onan 7500 quiet generator too quiet!! won't start ??

I am a newbee to the community and the forum. Prior to the recent purchase of my 4307 Mountain Aire, I used this forum for allot of my pre purchase research and due diligence and found the IRV2 community to be very helpful nice people. I joined up right away.
My 7500 Onan has under 300 hrs and was just serviced according to the seller. When testing out the coach I found it difficult to start the genset but it finally caught and started up. I ran it for 5 min then shut it down. During our drive home from Pittsburg PA to Vancouver BC it would not start.She cranks and cranks but wont catch. It exhausts white smoke while trying to start. I went to through manual and online to determine the issue. I changed all fuses checked all levels primed and preheated and all appears good? My fuel level is now sititng at 1/4 tank on the coach dash gauge. Perhaps bleeding the fuel lines after the fuel filter?
Any suggestions? we would be grateful.
Thanks all.
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Old 01-12-2020, 12:11 PM   #2
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The trouble shooting flow chart at the back of my generator manual indicates that if the unit cranks but will not start but emits smoke, then:

check glow plugs (warm the fuel)
check for clogged spark arrestor or muffler. (let it breathe)

Question:

Does your unit require that you warm the glow plugs for 15 seconds prior to trying to start the genset?

Mine does, and especially if the temps are below 50 degrees.

Be sure the fuel level is above 1/4 mark. Some rigs will not run below that level to save fuel for operating the chassis engine so you can get to the generator shop.

BTW.....our generator is a Powertech 7.5kw but should have the same operating theory.
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Old 01-12-2020, 12:25 PM   #3
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Hi Deandec,

yes I have preheated it for up to a minute. Nothing. Weather temp was between 40-60 degrees most of the trip and tried it with a full tank of fuel to 1/4 tank. lots of cranking power too.

any idea how to test glow plugs?

I will check the spark arrestor and check the exhaust for blockage.

thanks, appreciate your advice.
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Old 01-12-2020, 12:54 PM   #4
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Hi I had the same problem in my 7500. The temp sensor on the Tsat housing was bad changed it now starts like new. hope this helps
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Old 01-12-2020, 03:07 PM   #5
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Sounds like the glow plugs aren't warming up the cylinders. I bought our used coach (our first) in Mesa, AZ in January. It took quite a while of cranking for the QD8000 to start. The dealer claimed it was because it had been sitting on their lot too long. Not knowing anything about generators I accepted his explanation. The ambient OATs were in the mid to high 70s.
The first night on the way home I stopped in Deming, NM. The generator would not start. The next night was in Denver, CO. The generator would not start. The OATs in both locations were 25-30°+ colder than in AZ.
I took it to RM Cummins where, $600 later, they found and replaced a temp. sensor on the control board. At least that's what I was told. What did I know?
Apparently you can start your generator without glow plugs if you crank long enough and it's warm enough weather.
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Old 01-12-2020, 03:37 PM   #6
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I would fill the main fuel tank and see if you still have the problem!
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Old 01-12-2020, 03:46 PM   #7
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Your main fuel tank needs to be well above 1/4 tank.
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Old 01-12-2020, 04:36 PM   #8
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White smoke

Not enough fuel being supplied to run or start unit.
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Old 01-12-2020, 04:53 PM   #9
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Most coach builders keep the Onan fuel pickup tube positioned at 1/4 tank level so it won't run the coach out of fuel. Normal situation that can be remedied at your local fuel station. Ours runs out at about 1/3 tank level.
White smoke is indicative of no fuel.
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Old 01-12-2020, 06:00 PM   #10
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As the others have said, you have to have more fuel in your tank to run the generator. Once you fill up the coach, you will need to prime the generator before it will run.
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Old 01-12-2020, 06:38 PM   #11
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Driving from PA to BC I imagine he has spent quite some time with more than a quarter tank of fuel.
I and others responded previously to this identical question posted previously. My money is on no electricity getting to the glow plugs.
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Old 01-12-2020, 09:44 PM   #12
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Other poster mentioned glow plugs what is temp where you were when it first happened.Weak primary ,fuel pump , fuel pump sucking air somhow..plugged fuel filter .Or you ran it out of fuel and it not wanting to prime.
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Old 01-12-2020, 10:28 PM   #13
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Put some antigel in your fuel as well, you have taken a coach with #2 diesel in it , in all probability, into #1 diesel territory. You'll have to wait for a warm day or stick a space heater under the tank and gen to start it and flush the line. White smoke is what they do.
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Old 01-13-2020, 07:22 AM   #14
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Go to the Files section (above left) and do a search on Onan. You will find the manuals for your generator which may help you.
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