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Old 01-23-2012, 12:06 PM   #1
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Onan generator turns but won't start - again

I know this is a common post, but I'm needing something simple to find.
My Onan 7.0 turns freely with the generator's starter switch, but it dies after the switch is released.

I added 20gals of gas to the tank, thinking the generator pickup was not being fed, but that didn't help. The gas tank is 75gals, so I can't believe that it wouldn't start with 20gals.

Is it possible that there is a generator switch inside the coach that must be turned on to start? Is this common?

Is there a fused circuit that has to be checked? I kinda don't think that there would be one.

I'm worried that it's in the oil pressure circuit.
Is there a way to bypass this oil-pressure shut-off circuit to test it?

Any other ideas?
Thanks.
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Old 01-23-2012, 01:01 PM   #2
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Need help with Onan generator, starts and dies
Check this out under search;
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Old 01-23-2012, 01:06 PM   #3
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Baloo,

You need to add some more information.
1. When was the last time you ran the generator?
2. Was the gas tank completely empty when you added the 20 gal of gas?
3. Does it have plenty or oil in it?
4. What year/model is the coach?

If the gas tank was completely empty 20 gallons of fuel might not be enough. It is an estimate that the generator will stop when the gas tank is at 1/4 of a tank full. If the coach is setting on a slope the gas might not be getting to the pickup hose.

You say the generator turns freely but does the engine try to fire?

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Old 01-23-2012, 01:12 PM   #4
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The gen starts on 12Volts from the battery, but then MUST generate 12Volts to keep running. If it runs on 12 volts while you hold the start button down and stops when the button is released, #1 You have a bad board, #2 the 12 volt circuit in the rotor is bad.#3 too much oil or too little oil. these are the most likely problems.
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Old 01-23-2012, 04:57 PM   #5
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Quote:
Originally Posted by baloo View Post
I know this is a common post, but I'm needing something simple to find.
My Onan 7.0 turns freely with the generator's starter switch, but it dies after the switch is released.

I added 20gals of gas to the tank, thinking the generator pickup was not being fed, but that didn't help. The gas tank is 75gals, so I can't believe that it wouldn't start with 20gals.

Is it possible that there is a generator switch inside the coach that must be turned on to start? Is this common?

Is there a fused circuit that has to be checked? I kinda don't think that there would be one.

I'm worried that it's in the oil pressure circuit.
Is there a way to bypass this oil-pressure shut-off circuit to test it?

Any other ideas?
.
If you apply common logic to this, It can't be gas. When you hold down the start button it doesn't magically make gas and start. If it didn't have gas, It would never start. You are bypassing all the safety systems in the start position. (start button pressed) After you release the start button, the control board takes over. It is sensing a fault or there is no 12volts from the generator.
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Old 01-23-2012, 05:28 PM   #6
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Quote:
Originally Posted by ga traveler
The gen starts on 12Volts from the battery, but then MUST generate 12Volts to keep running. If it runs on 12 volts while you hold the start button down and stops when the button is released, #1 You have a bad board, #2 the 12 volt circuit in the rotor is bad.#3 too much oil or too little oil. these are the most likely problems.
I agree to disagree, if it trys to start when you hold it down and stops when you let go it Could be a bad board, it could also be on little wire that runs from the board way back to the rear of the unit(not sure what it connects to) if that one wire is broke or rat chewed on your gen will do as described.
If you have a 75 gallon tank with only 20 gallons of gas your pick up tube may not be in the gas- so no gas to genset. Are you sure it is running when you hold down the start button on only attempting to run? Could also be a collapsing pick up tube in the tank.

If you look in the files section of the IRV2 website you will see I uploaded the service manual for a 7kw Onan genset. Happy troubleshooting. Ron
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Old 01-23-2012, 06:32 PM   #7
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How many times did you try it. If it sat for a while, you will need to press the switch to the stop position for ~20 seconds to prime the carburetor.
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Old 01-24-2012, 05:14 AM   #8
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Alrighty. Thanks for all the contributions.

In response to some of the questions:
1) This is an 03 Gulfstream Sun Voyager that I just purchased used - 15,500 miles.

2) It is likely that the genset sat for over a year without starting. There was a note in the coach evidently from the previous owners saying that they could not get the gen to start, and that they thought maybe there wasn't enough fuel or that it was "bad gas" (although the vehicle's engine runs fine). I will squirt down the carb (if I can get to it) and maybe drop the bowl (again, if I can access it) to remove any lacquer that may have formed, or release a sticking float or needle.

3) The gas gauge was registering above the empty mark (but probably less than 1/8) when I put in 20 more gals -- but then I drove it about 25 miles, which probably means I burned up 5 gals. However, the gauge registers just under 1/4 full, if the gauge can be trusted. I will add 30 more gals of gas, along with an overload of fuel system cleaner

4) I had changed the oil and filter (and filled the filter up). After quite a few turns of the starter (and it trying to catch), I checked the oil level and it was dead middle -- not too high or low.

5) When I hit the starter button, the gen distinctly catches, with all the exhaust and rev noise appropriate for a firing engine. Since I have done this repeatedly and it fires every time, I guess "ga traveler" is correct that it must be getting fuel, or I would have emptied out the carb bowl of any remaining gas by all those attempts.

6) I did not know the gen has to be producing electricity in order to run! The logic does not make sense to me (the designers of this failsafe must not realize that it confuses any troubleshooting), however, I'll deal with this new twist and read about how to check that angle.

7) I did search "Need help with Onan generator, starts and dies " (good info there -- I can feel the poster's pain), and I went to the Flight Systems website and downloaded the troubleshooting manual. Unfortunately, it does not cover the Marquis Gold 7.0 HGJAB because they say it has a microprocessor that combines several controls and makes it impossible to easily service (!).

8) I'll check for "that little wire that runs to the back of the genset" to see if it's got continuity.


I now have to wait for the RV to come back from Workhorse Service, where it's having the brake recall being done. Frustrating to not be able to run out there and try some solutions.

Will keep you posted. I hope this is something simple, but I'm guessing I'll end up getting a new control board, and probably a few more items, before I finally take it to a dealer, where they will recommend a whole new generator. I am a pessimist because of experience, not because it is my personality.
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Old 01-24-2012, 05:36 AM   #9
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Baloo - You can send your control board to flight systems and they will check it and repair if needed. I think it's around $70 to repair or $25 to test it. At least you will know if that is the problem. You can call and talk to the person doing the testing/repair if you want. Real customer oriented company.
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Old 01-24-2012, 05:42 AM   #10
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A previous coach we owned had the same problem. The fix was a new fuel pump. What I believe was happening is the old fuel pump was putting out some pressure, enough to start, but not enough to fill the carb bowl and keep the generator running. Once the generator started it ran out of gas as the fuel pump could not keep up with the demand. I replaced the fuel pump and never had a problem again!
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Old 01-24-2012, 06:05 AM   #11
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Does the switch have a light that blinks after shutdown? If so count the blinks and check the owners manual for the trouble shooting codes and that will tell you what the problem could be. You should be able to find the owners manual on the onan web site. Good Luck JP
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Old 01-24-2012, 06:05 AM   #12
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baloo, My genset did the same thing. I sent the circuit board to Flight Systems. They checked it and it was fine. I ordered a voltage regulator from Flight Systems and replaced the old one with the new. It cranked and ran great. This happened two times with me. Both times it was the voltage regulator.
Now I know not to run both air conditioners at the same time off the generator for a long time in super hot weather. They ran a long time. But, finally the regulator quit.
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Old 01-24-2012, 08:39 AM   #13
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Quote:
Originally Posted by baloo View Post
Alrighty. Thanks for all the contributions.

In response to some of the questions:
1) This is an 03 Gulfstream Sun Voyager that I just purchased used - 15,500 miles.

2) It is likely that the genset sat for over a year without starting. There was a note in the coach evidently from the previous owners saying that they could not get the gen to start, and that they thought maybe there wasn't enough fuel or that it was "bad gas" (although the vehicle's engine runs fine). I will squirt down the carb (if I can get to it) and maybe drop the bowl (again, if I can access it) to remove any lacquer that may have formed, or release a sticking float or needle.

3) The gas gauge was registering above the empty mark (but probably less than 1/8) when I put in 20 more gals -- but then I drove it about 25 miles, which probably means I burned up 5 gals. However, the gauge registers just under 1/4 full, if the gauge can be trusted. I will add 30 more gals of gas, along with an overload of fuel system cleaner

4) I had changed the oil and filter (and filled the filter up). After quite a few turns of the starter (and it trying to catch), I checked the oil level and it was dead middle -- not too high or low.

5) When I hit the starter button, the gen distinctly catches, with all the exhaust and rev noise appropriate for a firing engine. Since I have done this repeatedly and it fires every time, I guess "ga traveler" is correct that it must be getting fuel, or I would have emptied out the carb bowl of any remaining gas by all those attempts.

6) I did not know the gen has to be producing electricity in order to run! The logic does not make sense to me (the designers of this failsafe must not realize that it confuses any troubleshooting), however, I'll deal with this new twist and read about how to check that angle.

7) I did search "Need help with Onan generator, starts and dies " (good info there -- I can feel the poster's pain), and I went to the Flight Systems website and downloaded the troubleshooting manual. Unfortunately, it does not cover the Marquis Gold 7.0 HGJAB because they say it has a microprocessor that combines several controls and makes it impossible to easily service (!).

8) I'll check for "that little wire that runs to the back of the genset" to see if it's got continuity.


I now have to wait for the RV to come back from Workhorse Service, where it's having the brake recall being done. Frustrating to not be able to run out there and try some solutions.

Will keep you posted. I hope this is something simple, but I'm guessing I'll end up getting a new control board, and probably a few more items, before I finally take it to a dealer, where they will recommend a whole new generator. I am a pessimist because of experience, not because it is my personality.
As per #6 it does not have to make elec. to run. It can run fine and not make 120 volts. It does have to make 12 Volts to keep running. As per #8 the little wire is the wire to the oil float. Too little oil or too much oil and it will not stay running.
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Old 01-24-2012, 05:22 PM   #14
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Good comments, thanks to all:
1) Good to know about Flight Systems being able to check the control board and rebuilding, if necessary;
2) I'll be aware of the fuel pump; I imagine this is an electric pump? I should be able to disconnect a gas line and check the pressure. Will add to the list. Sunnovagun.
3) Yes, I have a blinking switch, and I am anxious to check it as soon as the RV comes back from the brake recall.
4) Voltage regulator! I'll work thru the control board then check the VoltReg, or is there a way to do a regulator check?
5) Thanks for the info about the 12V - I will have to check how I would check that, without the genset running. The wire is to an oil "float"?? Really? A float? If it's like a gas float, I wonder if it could get stuck in an overly LOW or HIGH position. Is there a way to bypass this on/off float?
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