Onan RS12000 NG Not Starting

Do you do regular maintenance on it?

Thanks Tom, yes I get regular annual maintenance but with only 111 hrs on it, it has not been run that much to require it. 20 of those hour are probably from 'exercise'.

If the generator is giving you trouble and it costs you about $1000 every time the service technicians come out then I think it's time for a new generator.

You do not have the reliability you desire, sell the old generator and install a new generator is my recommendation!

What have the Cummins techs said was wrong each time?? This should be a very reliable unit...but truthfully if you are not comfortable troubleshooting and working on this generator yourself, you have little choice other than to replace the unit...on the bright side you should be able to get more than a few bucks for the old one...they use a Subaru EH 72 engine with Cummins Onan designed fuel system...

http://cr4.globalspec.com/thread/88153/ONAN-RS-12000-Overcrank

https://www.cumminsonan.com/www/pdf/specsheets/a-1534.pdf

Thanks for the reply SolarEagle.

I have had the demand regulator replaced, the wiring that was chewed away by rodents replaced, the brass adjustment screw on the demand regulator adjusted and each time, it runs fine, but once they get it running the thing is warm so doing a confidence test is easy.

What I want to ensure is that when the things is cold and we have a wind storm or it is cold because it's -5F outside and snowing that it starts up as soon as it senses power is lost like it used to. With only 111hrs on this thing, I cannot understand why it is not operating like it used to.

Do you do monthly inspections and try outs? If you are depending on this generator to start and automatically transfer, you need to do monthly testing and verification!

That is how it's done by the big corporations that need 99.999% electrical up-time!

No Original_Macgyver I don't do monthly load tests. It exercises monthly when it is set up and working properly but that is about it. I bought this to give me the peace of mind that it would start up automatically for my family if I was travelling with minimal maintenance required on my part.

I would run it longer and more often....once a week for 20 min....the gas sometimes becomes contaminated sitting in the line for long periods of time....I would purge the line....it sounds like you have a long run, it takes a while to use up that much NG...$1000 for what they have done seems excessive, I would look for a small engine repair person....somebody who is familiar with NG run engines...all these small generators require constant fiddling when they get that old....the only way to make it reliable is to become an expert on it yourself and stock parts and do maintenance and repairs when needed....or buy new every 10 years or so....

I am going to try removing the air filter to see if it starts as was discovered in the Overcrank discussion.

I am also interested in what I read in a different thread where it was suggested pouring a teaspoon or two of gasoline directly into the carburetor and starting it to see if that will burn off any air bubbles or water vapor and kick start the natural gas burning. Seems dangerous. Is that a real troubleshooting step???

Additioanlly, I am going to look for a local licensed electrician to work on this rather than calling the Cummins guys. I always thought that I needed a specialized guy for these things because it involves a mechanical, electrical and gas understanding not to mention generators themselves.

If you find yourself a mechanic that is also well versed in electrical controls you could let him have a whack at it.

Give him the entire story and see what he says?

I understand the part of wanting it to fire and run for your family when you're not there to help it along.

If you find a good mechanic, maybe have him do the monthly exercising when you're not there?

One of the biggest things I ran into when I was in charge of exercising 3 very large Onan gensets was the batteries would get weak and not crank hard enough to fire. The next thing was the oil sensors then the fuel sensors would get stuck and cause a non start.

I wish you the best of luck in finding a reliable mechanic to fix your troubles!

Bryan

The control systems for those and other units have become much more sophisticated over the past 10 years. I'm familiar with a Kohler 20KW NG unit and the operating principles are similar.

When you have a "didn't start" condition the control panel should tell you what failed to operate properly. "No crank" is entirely different than "Failed to run". The fact that you could start it manually (via the battery) rules out almost everything except the contact closure that provides the automatic start.

"Failure to continue running" usually is related to fuel problems. Something that's often overlooked (and not necessarily monitored by the control system) is a change in the fuel pressure and/or delivery capacity/rate. If there's been a lot of new development in your area it is possible that the gas mains pressure has dropped as new customers are added. When your unit was first installed the pressure may have been so high that a PRV (Pressure Regulating Valve) was installed in your service line ahead of the meter. It's possible that it's set for a higher line pressure than is currently available and it won't lift enough to pass enough gas to your fuel system, you'll need the cooperation of your gas company to check that their equipment is adequately sized, operating properly (PRVs are known to stick and fail-closed), and can supply your demand.

The other thing to check is the condition of your feed from the meter to your generator, especially if it's direct buried. There's a chance that it's been deformed if the foundation has shifted, and it can no longer support the required flow. The other potential problem is the buildup of condensation in the line, especially one that goes into a constant temperature zone in soil.

Gas companies put a small amount of water vapor into the gas stream to keep the seals and joints from drying out, hardening, then leaking. Your buried pipe is cool enough to condense undesirable amounts of water that then get sucked into your fuel system. To make matters worse, you have a large "drip loop" that will trap that water in the lowest point of your system, in ten years enough water may have accumulated to reduce the effective flow through it, and possibly send slugs of water into your fuel system.

The last point of concern would be the pipe routing and material. Hopefully it is not galvanized pipe which is affected by the moisture, and is instead black iron pipe which isn't. Also the route should be level with no appreciable dips or rises, all of which contribute to trapping of moisture. If you're considering replacing the generator, make sure the existing line is thoroughly cleaned and inspected, otherwise your fuel delivery problems will cause new problems.

One more thing, don't try and make any adjustments to the fuel metering system, that's definitely "trained technician with proper instrumentation" territory, trial and error can definitely cause big problems for starting, running, frequency regulation, and/or load acceptance.

RAMConsult - thanks for the well thought out advice. I appreciate it. It sounds like getting the line blown out and asking the utility to give me a report on the flow rate from the meter and also testing it at the generator is necessary.

Can you tell me what the correct spark plug gap should be for these units. I am going to check that I am getting a spark and while I am, make sure the gap is set correctly.

What can I do to make sure the demand regulator is operating correctly?

Good thought on the spark plug gap, but natural gas is clean burning and the plugs haven't seen much use. If they're severely fouled then it really does point to a severe fuel contamination problem. There should be a sticker somewhere inside the unit that gives the plug number, heat range, and gap information.

Before my son could get a construction permit for his Kohler the local gas company came out and did a capacity test on the existing service line whose only load was a 100,000BTU furnace. They had to replace the old line with a new 2.5" line along with a larger meter, high capacity regulator for the generator and a new regulator for the rest of the house. At full load the generator consumes over 380,000BTU/hr.

The nice part about the newer units is that they can communicate with most home automation/alarm systems. He can check the status of the unit, whether there's a utility outage, and if it's running properly from his cell phone; very handy if you're far away and a tree limb takes down your service entrance cable.

A month is a long time for the unit to stand idle, his automatically starts and runs 30 minutes every Sunday but doesn't take load. If there haven't been any outages I initiate a manual transfer once or twice a year to make sure the ATS (Automatic Transfer Switch) actually transfers on loss of power and the generator accepts full load.

I've lost the plot here. Is this gas as in domestic gas or gas as in gasoline which fuels the generator?

Natural Gas from my utility coming to my house and then to the generator.

Based on your own analysis, "worked great the first 3-5 years we owned it and over the past 3-5 years it has been so problematic and never starts automatically anymore" my advice is to just buy a new one every 4 years.

Thanks lyn.

Quick and easy test! It is ether fuel or spark!

Give it a shot of starting fluid. If it is fuel it will start up. If it is spark you get nothing.

Thanks fliptop427, but is that safe? I have a generator that was designed to run on Propane or Natural Gas and not gasoline or anything else. Isn't putting starter fluid in the carb the equivalent of putting some gasoline into the carb? What effect would that have on an engine not set up for gasoline?

Found this...

http://www.subarupower.com/wp-content/uploads/2014/09/subaru-engines-eh72-lpng-owners.pdf

https://en.wikipedia.org/wiki/Starting_fluid

If you want a mechanic familiar with NG/Propane powered engines contact a fork lift repair shop. Ask them for the best gas (vapor) mechanic they have to check and/or service your engine. Many, if not the most, fork lifts are powered with propane gas. The major difference between a natural gas unit and a propane unit is simply the propane unit has a preheater on the fuel line to change the propane from the liquid that comes from the propane cylinder to make it gaseous propane vapor for the engine.

If this mechanic has serviced power generators before he probably can help you on the generator end of the unit.

Another alternative would be to call in a Kohler or Generac service person. They love to fix the things the competition can't figure out.

Good Luck, Old Salt

This is incredibly bizarre, even for you.

I'm not looking for a debate, you know how I feel about arguing with fools.

Akinisky, I see that your generator runs, sometimes... as far as power outage start up, this could be a trigger issue with your volt drop timing.. This may be computerised with the landline low voltage and generator start up, then the master switch switch over controller.. Manually starting, is that jump starting with batteries or starting with just the push button starter. NG fuel, is your fuel/gas tank above ground or underground? I see your fuel line drops under the house, this may be a temperature change of the fuel, and your line may also have corrosion, it may be freezing through the fuel manifold, which stops the flow after 30 minutes. I would check the NG pressure at the generator fuel pump as it's running for more then 30 minutes, more like 60 minutes.. This should tell you if the fuel delivery system is plugged up after 30 minutes or more.

Thanks CW4 Murray.

The update is that the unit will not start on its own. I am able to to consistently start the unit with starting fluid sprayed into the carb. Then it will run continuously.

If it wont start on its on, but it will run fine with starting fluid, does it come down to the demand regulator being bad? If so, how do I validate that the demand regulator is bad?

Just like an automobile engine there is a "cold start" system that injects extra fuel (NG) into the manifold which turns off after the engine comes up to speed. And just like a car, when that system gets clogged up or fails to engage, the engine fails to start and continue running because the lean mixture won't fire properly. When you add starting fluid you make the mixture richer, it starts and runs up to speed.

Clean out your fuel system and check that the cold start system is operating properly but since this is NG, you need special techniques to inject the cleaner into the piping. You can remove the carburetor/injector system and try cleaning it out with automotive carb cleaner, then get a rebuild kit with new orifices, needle valve, seats, and gaskets, but one screw-up here and the engine will run at the wrong speed, or worse, you'll release NG into a closed compartment with hot surfaces nearby, A perfect scenario for an explosion.

Get a professional to do this...now!!! And stop twiddling with anything to do with the gas supply, regulators, valves, piping,etc. , no offense but you're above your pay grade here. Your insurance will not pay off if you flatten your house.

Thanks RAMConsult.

I would prefer that a pro resolve this issue, but as I stated, I paid $1000 last time the pro came out to troubleshoot it. My sense is that he gets it running and warmed up with starter fluid, but that doesn't solve the "it wont start independently when cold" issue.

If it can be resolved by replacing the demand regulator, then I just need to order one and get a friend who is comfortable with this kind of work to help me replace it. If it involves the cleaning described by you above, then I need to get a pro back and bite the bullet.

Find someone local who does propane and/or CNG conversions for automobiles, he'll know exactly how to service your engine. You're wasting time and money playing with the regulator, there's only a few moving mechanical parts, your electronically controlled fuel system on the other hand...