Onan LP Generator Problem UPDATE with new ?

[cahner]

Hello,
I have an onan 3600 LP generator. It has only 92 hours on it, very little use by me or the original owner. I originally tried to T into the propane line post crossover regulator and discovered that the gen set was being starved for fuel and ran it off of dedicated bottle. It runs intermittently. Once started it will run the water heater, microwave or AC. After about 20 or 30 minutes is bogs down and will begin to sputter and die. When restarted it will sometimes take the load of the AC and sometimes will not. It will take the load of just the fan without bogging down.

Any ideas are welcomed.

Thank you,
Casey

[alanmikkelsen]

I have the same generator and had problems all last summer. It runs off a dedicated bottle, also. The house bottle (furnace, etc.) ended up having a bad regulator, after I replaced a furnace circuit board (grr). After replacing the regulator on that bottle, I decided I'd replace the regulator on the generator bottle, and guess what? The generator runs fine! Regulators are cheap, you might try putting a new one in. These were about 10 years old and both had failed, apparently.

[Sam_Spade]

You need to get the hot-restart current draw of your compressor tested.
The A/C may need service OR the gen may be a bit too small.

If the A/C is going bad, getting a bigger gen will just postpone the pain.

[cahner]

I have everything set up and in place as it is designed with the on demand regulator. The gen set seems to run fine. It handles the load of the AC and water heater easily. After about an hour if the AC turns off it kills the gen set when it restarts. It handles the fan and then dies when the compressor kicks on. It will restart and do the same thing until it cools down completely.

I need your ideas please.

[MEXICOWANDERER]

I used to pour boiling water over the vaporizer to determine if it is the problem. State law requires a shutdown switch chop gas when the engine fails to run in California. Some are oil pressure activated, others are vacuum activated. The shutdown safety is manually bypassed while cranking.

[cahner]

Ok, I finally bypassed the KN on demand regulator and ran the fuel from the bottle to the fuel lock off and then directly to the carb. It runs great. The 2 stage regulator that comes off the bottle reduces the pressure to 10 lbs in the first stage and 11" water column in the second stage.

This makes me ask why is the on demand regulator needed, or is it?

[cahner]

Okay, I played with it a little more tonight. It will start when primed with the prime button and then will run great with the prime button just barely pushed in. When pushed in it is over fueled and will die, when not pushed in a little it is starved. The new kn has a 7/16 office and is a 6 oz regulator

Any ideas?

[cahner]

I do not believe that a safety is the problem. I bypassed the fuel shutoff and ran directly to the regulator and verified it has oil. I would think the murphy switch would shut it down, as is should, but would not let it continue to run although at lower speeds.

The only way it will continue to run is when the prime button is held in the entire time.

[marcsbigfoot20b]

I just had the same problem on my Onan 2500LP.
It was hunting under no load and had trouble keeping up when the load was applied.

Used carb spray to verify while it was hunting under no load that it was running lean. A spray and it ran great.

I also have the SD demand regulator. I bought the rebuild kit on Amazon for $68 maybe 4 weeks ago. SD regulator kit
Installed it and it ran perfect, just had to adjust the gov linkage since I had messed with it during trouble shooting.
I think the spec says about 62.5 Hz and 123 volts at no load.

[MEXICOWANDERER]

Did you verify the SAFETIES are not malfunctioning? LPG engines have either a vacuum or electrical valve fuel cutoff. The electrical usually runs through an oil pressure switch, the vacuum off the carb base port fitting.

[cahner]

The problem was the regulator diaphragm. The sd regulator is no longer made and had to replace it with a kn model. Got it all hooked up and everything was great. Let it run for about a minute and then put it in the trailer. Now it will not run unless the prime button is held, even then it runs at only about half speed and acts as if it is starved for fuel and dies if prime button is not held. Took it back out and checked to make sure nothing in any of the lines and bypassed fuel shut off.

Now I am really baffled. Any ideas are appreciated.

Thanks,
Casey

[wolfe10]

Let me slightly restate that:

A liquid LP generator WILL run just fine on HIGH PRESSURE VAPOR (i.e. "T" off before vapor regulator that supplies the house appliances. Have many hours of running a Liquid LP Onan like this after in-depth discussions with engineers at Marshall Gas and Onan. And, while you could still get contaminates leaching from the hose, you will NOT get any long-chain hydrocarbon contaminates from the propane, as those do not vaporize.

Agree, if you are supplying it with vapor downstream of the regulator (i.e. under 1 PSI of pressure) it will not work without modification.

[MrWizard]

I think your Onan is fuel starved
my Onan LP is Liquid Fed from the bottom of the Horz tank
there is vaporizer where the carb would be
there is an inline regulator for pressure from the liquid

to run from a Vapor line, such as used by stoves and water heaters
requires a change in the LP hard ware on the Onan

a conversion kit from liquid to vapor

I don't have a part number, but i know they are availble
but third party
I don't think they come from Onan/Cumins

[cahner]

It has taken me a little time to get back to the generator. I have checked to make sure that the tank pressure isn't dropping or fuel freezing. The last time that I attempted to start it it would kick over but would not run. It would hunt and search and finally die between 30 seconds to a minute. Has oil.

Any ideas would be great so I can start in the right direction

Thank you,
Casey

[Kayteg1]

Sam Spade wrote:
Fuel starvation does NOT automatically mean a freeze up somewhere.

Yes again, but when generator restarts fine after some sitting -that rules out bad regulator and several other things.
So cold tank dropping pressure goes to top of the list.
Installing one of those would easy confirm.