New Cummins 13KW standby genset won't start reliably

Cummins/Onan Air Cooled & Liquid Cooled standby generator troubleshooting and repair questions
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Paul999
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I recently completed installation of a Cummins 13KW genset (model C13N6H-A054E399, SN F180374250). It had been sitting on a pad without gas or electric hookup for about a year and a half. At first it would start with difficulty, at the tail end of three attempts, but now it usually fails and displays an overcrank failure code. When starting, the engine sounds like it is turning over fine but it doesn't 'catch'. The battery is new and shows 13.7Vdc. When it does finally run, it generates and maintains the proper AC voltage, at least under the relatively light loads (<10amps) I've exposed it to.
I checked the propane line (about 50 feet of 3/4 plastic line) during startup. The regulator (about fifty feet away) shows 12 inches of water with no demand and it goes down to high in the 11 inch range with the gen set cranking. I also checked one of the pressure taps after the open/close solenoid in the gen set itself. It has similar readings.
There is another pressure tap in the gen set that I believe is on the outlet side of its pressure regulator. It shows a zero reading when not operating and goes slightly negative (from 0 to -0.9 inches water) when it is trying to start. Based on this I assume the regulator has some problem. Does that sound reasonable? Do you know what the pressure reading on this tap should be?
Based upon its location it looks like it is not that easy to get to/replace. Should I be doing any other tests (spark?) before I take make the effort to buy and replace the regulator.
Any advice would be appreciated.
Chris
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Can you post a couple of pics of the piping and regular and how it's setup in relation to the generator's location?

If there's 50' of 3/4" pipe between the gen and regulator, that could be part of the trouble.
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Paul999
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The propane second stage regulator is on a building. It is a RegO LV4403B. It can deliver roughly 4 times more gas than the gen set alone needs without significant pressure drop. The piping to the right in the photo (that goes into the ground) is a 50foot underground. line to the genset.
propane line at building.jpg
propane line at building.jpg (156.29 KiB) Viewed 159 times
Here is the piping at the genset.
propane line at genset.jpg
propane line at genset.jpg (189.14 KiB) Viewed 159 times
Finally, the photo below shows the fuel supply assembly from the Cummins parts manual. Fuel enters the genset through dual solenoids on the bottom left (item2)-pass thru a regulator(4)-then a NG/LP orifice set to propane(8)-then goes through a hose to the mixer on the engine(9). I took manometer readings at the outlet of the solenoids and at a pressure tap marked (14) which I think is the regulated pressure.
cummins 13KWgenset  fuel supply.jpg
cummins 13KWgenset fuel supply.jpg (23.3 KiB) Viewed 159 times
When I try to start the engine, the pressure at the building and just past the dual solenoid drops a little and is just below 12 inches of water. The Cummins installation manual says the genset wants to see an inlet pressure at full flow of 6 to 12 inches of water so I suspect the supply line is not the cause of the problem. What I'm struggling with how the regulator is supposed to behave (pressure while starting or operating). Currently while trying to start there seems to be a slight negative pressure created. That doesn't seem right but I have no idea what to expect. There is a screw on top of the regulator but I'm not sure it is meant to be adjusted.
Chris
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I can't imagine that the negative pressure is normal... That would indicate that there is zero gas pressure and the engine is pulling a vacuum on the system. Are there any signs of mud wasp or spiders nest on the vent device on the regulator inside the unit?

At 11" W.C. and 50' with 3/4" pipe, LP is good for about 255K BTU from the chart I have.
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Paul999
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Hi Chris,
Thanks for the quick replies.
The regulator is surrounded by a foam block* so it is hard to inspect but I don't see any sign of insect nests near it. I must say though that when I first got the genset running a lot of material went flying and I found a mouse nest on (but not through) the paper of the air intake filter. I replaced it. So maybe...
My first thought was what you first wrote- that the fuel supply, either the piping or regulator at the building was too small, but that doesn't seem to be the case. Now I'm thinking maybe some stuff (like a spider nest) got into the inlet line when the genset was sitting around for so long. The mystery though is that when I can actually get the gen set running it seems to run fine. I don't know what the inside of a regulator looks like so I have no idea what to expect if it somehow got fouled. Nor do I understand the settings for this one and I can't find any documentation online or at the Cummins website.

I'm not an engine guy, much less a propane engine guy, but I know enough to know that if I have air (which I do), spark, and fuel it should run. As far as spark goes, if I can get it to start it runs fine so I think spark is not the issue either. By the way, one other observation that might be helpful. Once it has been running I can turn the genset off and try to start it again. It starts within a few seconds consistently.

*It looks like the regulator has some sort of heater line going to it and I suspect the foam is meant to provide insulation.

Again, appreciate any thoughts. I have no Cummins trained folks near me so I'm kinda on my own unless I want to fork over $350+ in tech mileage costs alone.
Birken Vogt
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Slight negative pressure on the output of the demand regulator is normal. -0.5" or so is what they are usually set at.
Paul999
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RE: demand regulator setting

Thanks for the info on a -0.5 inches of water setting. That's what I'm seeing. When the engine is cranking the manometer pressure reading bounces around between 0.0 and -0.9 but mostly around the middle of that range.
Looks like my problem may be something else. maybe.
Chris
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I'm glad Birken cleared that up! My knowledge of Cummins gear is pretty limited. I've never seen a step down regulator like that have negative pressure on the other side.
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
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