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Full Throttle Generator


Nevada Rob
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I am still having generator issues with my 10K. The generator starts right up. After 10 or 15 minutes it will start to stall and puff black smoke then run great from anywhere between 2 minutes up to 2 hours. Some days it runs great, some days not so much. I have installed a new fuel pump, changed the fuel filter 3 times, checked for loose connections etc.. After a few adult beverages I have come to realize that when the generator is running, it is always running at full throttle. With no load or all three A/C units, refer, battery charger loaded on it the engine speed never changes. My previous RV's generators would throttle up as I put a load on it. My local Cummins dealer has ONE gen tech who is apparently out until further notice. I called 1-800-CUMMINS. The tech there said most likely a bad control board. I bought this hole in the pavement to pour money into a few months ago. It has had this issue since I brought it home. Anyone else have this problem? Cummins dealer wants $560 to diagnose then start adding on parts. Looks like a control board is anywhere from $850 - $950.

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Don't know what engine is in yours but it's got to have a full actuator that controls the high pressure pumps. I would take it out and check the plunger for free movement, it may be sticking. Before throwing money at it.

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2 minutes ago, Ivan K said:

Don't know what engine is in yours but it's got to have a full actuator that controls the high pressure pumps. I would take it out and check the plunger for free movement, it may be sticking. Before throwing money at it.

The guy at Cummins said the throttle is completely controlled by electronics. I asked about any stuck linkage, rods, broken return springs, bad muffler bearings, the whole enchilada. He said no on the the enchilada.

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Your 10kw generator is like mine.  It is a constant speed generator.  Did you check for trouble codes on the start switch light when it shuts off?  Did you also check the control harness plug on the side of the generator case?

Here is a link where you can download the service manual with troubleshooting error codes.

 

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5 minutes ago, Frank McElroy said:

Your 10kw generator is like mine.  It is a constant speed generator.  Did you check for trouble codes on the start switch light when it shuts off?  Did you also check the control harness plug on the side of the generator case?

There are no codes which is frustrating. I have checked the and secured the control harness plug as well. Does your generator run at a constant speed? Never slowing as the load is released from the generator?

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Yes, this is a constant speed generator independent of load.  Some of the smaller generators are inverter generators that vary speed depending on load.

Hmm, no codes.  Does your coach have a multiplex keypad in the rear bedroom to start and stop the generator?  I'm wondering if it's getting a false stop signal.  Also is the auto gen start controls turned off?  This could also be giving a signal to shut off the generator.

Trying to suggest the easy stuff first before throwing expensive parts at it.

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It does have a multiplex start switch next to the bed. Auto start is off. It does seem to stumble less with no load. That is why I was thinking fuel related. This coach sat for 2 years and never moved with a half tank of fuel. I am suspecting a very contaminated fuel tank. I have put in Bio kill and water treatment additives. I am through half a tank with the treatment. 

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"Yes, this is a constant speed generator independent of load."

According to the manual it reads that these are constant speed generator that match engine speed to load????? If "constant speed" then why say engine speed is matched to load??? That statement implies the engine speed changes.  It does not make any sense, a contradiction of terms. I may have to cancel Christmas for the grandkids and suck it up and take it to Cummins. Pay them $2,000 for a repair on a coach I am most likely going to sell off anyway.

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I am also having a heck of a time with my 10kw Onan.  It is surging or stumbling much of the time.  I have changed out the fuel and air filter, replaced the governor actuator, and now the fuel pump, it is still doing it, almost quits but not quite.  It is finally throwing a 36 code.  It was suggested to me that perhaps the fuel line has a small crack or hole after all these years and is sucking air, so just had a new line made up, and will install it in a couple of days when I am stopped.  I have been using Onan troubleshooting and have done everything down to the next item on the list and that is the control board.  Hoping the fuel line fixes it, it sure acts like it has to be a fuel problem.

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Bill, one thing you can try is to run the fuel return line into a bottle to see if air is being pulled in.  The other thing to check are the brushes on the slip ring to see if they are past their service life.  The manual will tell you how to do this.  The other thing I found is that these generators like to be run at near full load periodically.  This cleans up the slip rings and you get a much cleaner AC sine wave output.

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9 hours ago, Nevada Rob said:

"Yes, this is a constant speed generator independent of load."

According to the manual it reads that these are constant speed generator that match engine speed to load????? If "constant speed" then why say engine speed is matched to load??? That statement implies the engine speed changes.  It does not make any sense, a contradiction of terms. I may have to cancel Christmas for the grandkids and suck it up and take it to Cummins. Pay them $2,000 for a repair on a coach I am most likely going to sell off anyway.

I believe Onan gens generally come in 2 types.   One is like mine,  an Inverter type.   Inverter types keep the power at 60 hz frequency electronically by the inverter and the speed changes according to the load.

Onans like yours keeps the speed constant in order to maintain 60 hz.  It may sound different as the load increases because the load demands more power in order to maintain a constant speed thus 60 hz.

If I'm all wet someone will let me know,  just take it easy.  😉

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Ray, you are exactly correct.  The 10k generators generate 60 hz by maintaining a constant engine speed.  As you increase load, the engine needs more fuel to maintain a constant speed.

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I have checked the brushes and they are fine.  It is puzzling, we ran it for 5-6 hours after we had replaced the actuator and it ran fine until it didn't, high load, no load has no effect.  After replacing the fuel pump it ran about 45 minutes fine until it starting surging and stumbling again.

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2 hours ago, willbo777 said:

I am also having a heck of a time with my 10kw Onan.  It is surging or stumbling much of the time.  I have changed out the fuel and air filter, replaced the governor actuator, and now the fuel pump, it is still doing it, almost quits but not quite.  It is finally throwing a 36 code.  It was suggested to me that perhaps the fuel line has a small crack or hole after all these years and is sucking air, so just had a new line made up, and will install it in a couple of days when I am stopped.  I have been using Onan troubleshooting and have done everything down to the next item on the list and that is the control board.  Hoping the fuel line fixes it, it sure acts like it has to be a fuel problem.

Exactly the same issue with mine. I would think a crack in the fuel line between the pump and the tank would leak fuel when it is not running. Even a small weep would show up over time. If air can go in, fuel can come out. I would think a leak would cause it to stumble more often or constantly. It is frustrating how it will run for 2, 3, or 4 hours perfect then start to spaz out and run like crap. It has to be hard on my electrical system and A/C units to have so many power surges. As a retired Fire Captain I have a hard time fixing things based on a guess or hoping something works. Hope is never a plan. This forum has great people with a ton of knowledge. I was pretty sure someone will have a solution or what they did to correct the problem. The tech at Cummins said he is 95% sure the issue lies with the control board. Best price I have found is $825 for the little bad boy. 

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I am so frustrated with it by now that I would pop in a control board if I was sure that was it.  I don't disagree on seeing a leak, I am sure I am reaching for straws and sucking a bit of air would cause the rough running.  I'll find out in a couple days, but I am leaning more and more towards the control board.

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I am leaning towards a new board as well. We have a trip planned for next weekend but may have to cancel. Running the A/C's on the road with the generator issues may cost new A/C units as well.

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Before throwing a new control board at the problem, I'd make sure there are no air bubbles or reduced fuel flow in the fuel return line going from the generator back to the tank when you are experiencing the problem.  A small piece of crud can easily block the fuel pump check valves causing reduced fuel flow.  A small leak on the fuel line inside the tank can also cause a fuel starvation or air in the fuel and not be seen until you look at the fuel return flow back to the tank   I'm not saying that the board is fine, just trying to be sure you eliminate a fuel related issue.

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I appreciate the input Frank. Thank you. The issue remains with a full tank or 1/4 tank, no difference. Are you saying there is a fuel pump check valve on or in the tank?

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Changing both the feed and return fuel line would eliminate this as a possible cause of the problems and would not be that expensive.  I know it's a pain crawling under the coach but if you have the fuel lines and tools it would be an in and out job.  While you have the lines off the fittings on the tank I'd check to make sure there are not problems there, you could pull the pickup tube out and check it just to make sure there is not any type of blockage.   

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3 hours ago, Frank McElroy said:

Ray, you are exactly correct.  The 10k generators generate 60 hz by maintaining a constant engine speed.  As you increase load, the engine needs more fuel to maintain a constant speed.

^^ This ^^

Your engine should be spinning 1800rpms from no load, to full load.

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2 minutes ago, 96 EVO said:

^^ This ^^

Your engine should be spinning 1800rpms from no load, to full load.

That sounds about right. Not very fuel efficient when all we need is to charge batteries or a crock pot all day while out camping. We boondock camp 95% of the time. Good thing I have my trusty Honda generators to put in service.

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I am with Frank on this. But having a spare controller if it does not work out isn't all that bad either, it holds value better than money in the bank 🙂 if you can get it that is.. Mine is made of unobtainium. There's not only the usual lift pump but also the somewhat complicated high pressure pumps per cylinder. One of them going out could cause what you are seeing. Same with injectors. Just think what the controller does to the engine, it turns the lift pump on and controls the actuator. That's it. Outside of monitoring the vitals. Since you have no codes, likely nothing wrong with the vitals. Black smoke indicates overfueling.. Could be purely mechanical. On mine, I would throw the breaker and run it with actuator removed to isolate electronics and see but that's just me and I have done it with my issues.

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