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Old 09-19-2017, 08:42 PM   #1
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Onan generator puzzle

Here we go again, just a few month past a five day shop experience the Cummins Onan 2.5 HGJBB-1125A LP generator again will not start. Give it a shot of starting fluid and she will purr right up and run, even under a good load. Shut off after an hour or so and she won't kick on without starting aid.

Any ideas? Similar experiences?

Just as a side note; a Honda EU2000 with a GenConnectX propane conversion sounds more and more tempting. I understand one of these will run the AC with an aftermarket soft-start installed. No more noise and vibration inside, quiet and trouble free. Perhaps not quite as convenient, but what is convenience if it does not work.
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Old 09-19-2017, 08:55 PM   #2
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It's a fuel problem. Is the generator propane only. If so problem could be in the regulator pressure being to low to allow for a clean start. Starter fluid is getting it up and going and then it is fine?
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Old 09-19-2017, 09:15 PM   #3
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It's a fuel problem. Is the generator propane only. If so problem could be in the regulator pressure being to low to allow for a clean start. Starter fluid is getting it up and going and then it is fine?
Regulator pressure on the main tank?

Yes it runs just fine once I get it started with s fluid.
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Old 09-20-2017, 01:30 AM   #4
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Not sure I can contribute to the diagnosis, I do have a question, how do you administer the starting fluid? Crawl underneath?

On the diagnosis, I heard from my Onan service company that Onan is tightening up the requirements to be a sales and service dealer. Your shop should stand by their work even a few months later.
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Old 09-20-2017, 05:14 AM   #5
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I never would have thought to give a shot of starting fluid to an LPG engine. And like Ryoungca am wondering where you would do so. Drop the spare tire, remove the rear cover of the Onan, and then (try to ) find the air filter?

The low pressure regulator has a vent tube that sticks out the bottom of the generator pan. My vent tube is covered by piece of foam 'filter'. But if yours isn't then it could be plugged. I think this would prevent both starting and running, but it is the easiest place to start. Then I would check the high pressure regulator on the LPG tank - unlikely but relatively easy to do. Then change the spark plug (again unlikely, but easy. Problem sounds like fuel, not spark or air.) Then check the low pressure regulator on the generator. I don't know if it is adjustable, or if you simply replace it. Carbuerators have starting (choke) fuel, idle jet, and a venturi that sucks more fuel as load increases. I don't know how the low pressure regulator handles starting/idle/load transition, but that seems to be at the heart of your problem.
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Old 09-20-2017, 05:29 AM   #6
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When all else fails, read the manual. After posting the above I looked on-line. See this link for troubleshooting. My suggestions above appear reasonable. Lots of good info in here (starting page 8-22) on the primary pressure (11 " H20) and the secondary (demand)regulators.

http://b190.com/files/Onan-Cummins%2...e%20manual.pdf
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Old 09-20-2017, 05:38 AM   #7
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Give it a shot of starting fluid and she will purr right up and run, even under a good load. Shut off after an hour or so and she won't kick on without starting aid.
Under the troubleshooting philosophy of "check the easy things first"— are all 120vAC loads switched off when you try to start the generator? Trying to start under a load could cause the symptoms you describe. And it's both easy and important to verify that all loads are switched OFF before trying to start the generator. Then let the generator run for about 20 seconds before you start adding loads. No matter if it's an Onan 2.5k propane-fueled generator, a Honda Eu2000i gasoline-fueled generator, or a big 100kw Generac SD100 diesel-fueled generator. Conventional wisdom is to never start it under a load.

And in your post you DID say "even under a good load" so from your own admission I'm tempted to chalk this problem up to user error. But further experimentation is required in order to verify the diagnosis.

Try starting the generator again NOT under a load as recommended in every generator user manual I've ever seen, and please let us know what happens. If it starts, then user error was the culprit. If not, then we can explore other possible causes.
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Old 09-20-2017, 05:44 AM   #8
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I don't believe the electrical load when starting matters as the generator will not accept load until a period of time has elapsed. On mine it takes about 2 minutes before the generator lights up the EMS. You can have all the load 'downstream' of the EMS that you want, but generator power does not reach that load until the generator is up and running.
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Old 09-20-2017, 06:03 AM   #9
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I don't believe the electrical load when starting matters as the generator will not accept load until a period of time has elapsed. On mine it takes about 2 minutes before the generator lights up the EMS. You can have all the load 'downstream' of the EMS that you want, but generator power does not reach that load until the generator is up and running.
Perhaps. Even probably. Almost definitely.

But my suggestion is easy to check, and even if it doesn't solve the problem then no harm has been done to try a "no load" start by manually switching off the loads rather than relying on the EMS to hide the loads until the generator is ready to accept them. All it costs is a few minutes' time— and no particular effort— to try it and see. After all, the problem may actually be the EMS. We don't know.

I used to be an engineer before I retired, and engineers have a reputation for seeking complex solutions to complex problems. Now that I'm retired, I'm trying to make sure we don't also apply complex solutions to potentially simple problems. So it only makes sense to propose a simple solution first, before proceeding to more complex ones if the simple ones don't work.

It's also important to offer the OP as many alternatives as possible. I'm not trying to downplay your experience or your advice to the OP. But I'm sure you would agree that one should try all of the alternatives that don't require crawling under the van before proceeding to the alternatives that do require it.
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Old 09-20-2017, 06:41 AM   #10
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Felixkagi,
Am I reading your OP correct that the Onan will start on LPG (rather than starting fluid) for a short period of time after it has been shut off, but not after a longer (>1 hour) period of shut-off? This could be a significant clue, though I am not sure what that clue means.

There is not a choke on an LPG engine, but I see from the manual that older gen sets have a 'built-in automatic priming solenoid' (see pg 8-23, 24 of the link). That may not be working correctly, but is only noticeable when the engine is cold.
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Old 09-20-2017, 07:54 AM   #11
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I had this same problem. We were getting propane to the furnace and cooktop but the generator would not start. The dealer measured my gas pressure getting to the generator as being about 25% of normal. They replaced a regulator and that fixed it. Evidently the feed to the interior appliances branches off before this regulator that feeds the generator.

Mark
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Old 09-20-2017, 08:15 AM   #12
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Originally Posted by Ryoungca View Post
Not sure I can contribute to the diagnosis, I do have a question, how do you administer the starting fluid? Crawl underneath?

On the diagnosis, I heard from my Onan service company that Onan is tightening up the requirements to be a sales and service dealer. Your shop should stand by their work even a few months later.
I have two ramps and a creeper to get under the car, remove the little cover, press the start switch that is right there a spray a little starting fluid into the air filter hosing. Quit simple though obviously I can't (won't) crawl under the rev overtime I run the generator.

The (Cummins) dealer that fixed it the last time? Well, that was on a trip and that shop is 1,200 miles away.
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Old 09-20-2017, 08:22 AM   #13
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Quote:
Originally Posted by Titus View Post
I don't believe the electrical load when starting matters as the generator will not accept load until a period of time has elapsed. On mine it takes about 2 minutes before the generator lights up the EMS. You can have all the load 'downstream' of the EMS that you want, but generator power does not reach that load until the generator is up and running.
That is correct; the generator does not start under load, it takes a few minutes before potential loads kick in.

The breather tube is free otherwise it would not keep running (with starting aid)

The priming solenoid works and gas flows through the line (removed the hose to check) so it could be something forward from there, the regulator or the fuel mixer?
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Old 09-20-2017, 08:26 AM   #14
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Felixkagi,
Am I reading your OP correct that the Onan will start on LPG (rather than starting fluid) for a short period of time after it has been shut off, but not after a longer (>1 hour) period of shut-off? This could be a significant clue, though I am not sure what that clue means.

There is not a choke on an LPG engine, but I see from the manual that older gen sets have a 'built-in automatic priming solenoid' (see pg 8-23, 24 of the link). That may not be working correctly, but is only noticeable when the engine is cold.
My description may not have been clear. NO the generator will not re-start on its own even after an hour of running. As I mentioned the priming solenoid works and lets fuel pass, since this is located on the outside of the generator I can check it.
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