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Old 02-21-2011, 02:29 PM   #1
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Onan 7.5 Diesel Genset generator will not start

The generator has been running fine. The last trip I took the generator was hard to start. After warmup period I put a load on and it would bog the generator some and would not take the load. I shut it down and in a little while I started it again and applied a load it ran for a short while and the generator shut down on its own. As I really did not need it, I did not run it again on the trip home. A week later I tried to start the generator and it would not start. I tried several times without success.
What occurs when trying to start: I press the control switch to Stop position to prime the generator for about one minute. The red light comes on and I can hear the pump pumping. I then press the control switch to Start position and the pump continues to pump and the red status light blinks during the preheat period (clicks about 10 sec) and the generator starter clicks once and stops. The starter does not turn the engine over. If I continue to hold the switch down the cycle starts over again with the same results.
What has been checked: The two RV batteries are fully charges and reads 12.6 volts. The battery terminals are all cleaned and good. The Genset battery terminal from the main batteries read 12.6 volts. The Genset coolant is at max level reading. The Genset oil level is at the full mark. There is no restrictions at Genset air intake. The air filter looks good. There is no visible leaks of any kind. The oil filter compartment looks good. The fuel filter and pump look fine. The starter and solenoid look brand new. All wiring and cables have clean connections. All items visible in the compartment look new.


The Genset has been a little hard to start for the past year. But once started it run fine and has had no problems running under load for hours at a time.
I would like to solve this on my own if possible. I live too far from the nearest Onan service dealer. It would be most inconvenient to have to take it there. Hopefully someone here can help.
Thanks,
Bob
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Old 02-21-2011, 02:45 PM   #2
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Hi yelvero,
Welcome to iRV2. I also have a 7.5 Onan (2005). If yours is about the same vintage, try starting the generator by pressing and holding the start button. This is what my instructions say to do. As I hold the start button, I can hear the startup cycle happening the generator will exit the startup cycle and actually start while continuing to press the start button. Once it starts, I release the start button. At no time do I press the stop side of the switch.

This may or may not work for you, but it is easy and cheap to try.
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Old 02-21-2011, 02:49 PM   #3
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Unhappy

Thanks for the response. Yes, This is exactly how I start mine. However, as I stated above it will not start.
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Old 02-21-2011, 03:13 PM   #4
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My 7.5 Onan has a start stop switch on the generator as well as two start/stop switches inside the coach. Just random thoughts: Have you tried all the switches and do you get the same result with each switch? Can you get close enough to the starter motor tell if it is actually engaging when the start switch is pushed and if the solenoid engages. You may have two problems - running poorly as it was initially may indicate low fuel - your filter may look good but be clogged. The starter not turning over could be another issue - can you tell if the click comes from the solenoid or from the starter. You could pull the starter and take it to a local shop and have it checked out.
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Old 02-21-2011, 03:52 PM   #5
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1ciderdog,
I have tried it at two out of three starter locations. I will try the third but expect it will do the same.
The fuel tanks is 1/2 full. So i do not think it is starving for fuel. The fuel pump is working. I can hear it pumping. However, I have not verified that it is pumping fuel. Not sure how I can verify this? Have not pulled the fuel filter. But it looks OK. As best I can tell the starter is not engaging. It sounds like the solenoid is making the click. I will try to verify this if possible.
Thanks,
Bob
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Old 02-21-2011, 07:05 PM   #6
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My guess is the fuel filter. No way that I know of to tell if it's good or bad by visual inspection. Also check for a second in-line filter. Don't know what make of coach you have but do know some manufacturers add a second in line filter.
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Old 02-21-2011, 09:03 PM   #7
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yelvero,
First, you must verify the starter and or solenoid are working..... Don't even bother with fuel in any way shape of form!!!!! If the engine isn't being turned by the starter, it doesn't matter nuttn bout the fuel system....
The engine has to be fully cranking first...... when you hit the switch and the "system" starts to work, at some point in time the engine must crank and continue to crank.... once it does that and still doesn't start... THEN look at fuel, air and compression issues!!!! Starter has to be making the engine go roundy round first!!!
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Old 02-21-2011, 10:24 PM   #8
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I had starting problems because I had gone over 150 hours without changing the oil filter....changed it and it started and ran fine.
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Old 02-21-2011, 10:38 PM   #9
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Try tapping the starter motor with a hammer while someone is engaging the switch. Could be a bad bushing letting the armature short out or a brush sticking.
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Old 02-21-2011, 10:57 PM   #10
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Quote:
Originally Posted by boots_h
Try tapping the starter motor with a hammer while someone is engaging the switch. Could be a bad bushing letting the armature short out or a brush sticking.
Careful about tapping the starter, it could damage the magnets and then you may need a new starter
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Old 02-22-2011, 07:41 AM   #11
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yelvero,
First, you must verify the starter and or solenoid are working..... Don't even bother with fuel in any way shape of form!!!!! If the engine isn't being turned by the starter, it doesn't matter nuttn bout the fuel system....
The engine has to be fully cranking first...... when you hit the switch and the "system" starts to work, at some point in time the engine must crank and continue to crank.... once it does that and still doesn't start... THEN look at fuel, air and compression issues!!!! Starter has to be making the engine go roundy round first!!!
I agree with your analysis. I will not know if I have a fuel issue until I solve the cranking problem.
It looks like I will have to remove the fuel filter in order to get to the starter and solenoid. Not very much room to work in there. Does anyone have suggested removal procedures to get to the starter?
Thanks,
Bob
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Old 02-22-2011, 10:32 AM   #12
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Measure it and sneak up on it!

Since this has been growing it could be an intermittent or hard failure, nothing would be worse than to "tap" it and have it work "for now".

It is now in a failed condition, so be very careful so you can measure the failure.

Get a voltmeter and measure the voltage at the selenoid, both the battery side and the signal to activate, if you hear it clicking then you may have the control line.

Next measure voltage to the starter, continue measuring voltages until you find the problem.

Since you stated that it is not cranking the started motor is not running, either the motor is bad, volts present at starter motor, or there is a power problem, no voltage to starter due to bad battery, battery wire, selenoid, control wire, or a possible shorted starter that causes the voltage to drop when activated.

DO NOT start wiggling and tapping, it may fix it only to have it fail later!

Good careful measurements will identify what to check next, take your time and you will find the cause, let us know what you find and good luck!
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Old 02-23-2011, 08:11 AM   #13
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1ciderdog,
. As best I can tell the starter is not engaging. It sounds like the solenoid is making the click. I will try to verify this if possible.
Thanks,
Bob

I wasn't indicating it was a fix. Only a quick diagnosis or an emergency measure. If "lightly" tapping the starter starts it cranking, then you know the problem is either a poor connection or bad ground or the motor itself and will need repair or replacement. Geeesh
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Old 02-23-2011, 06:46 PM   #14
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You're right yelvero. I missed the part about the starter not turning. My bad.
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