Cummins Onan LP 25 won't start...

[Howard_Woodard]

Hi all. I'd like to get some help with a 7-year-old Cummins Onan LP generator that won't start. I've tried to do as much as I can before potentially wasting your time on a problem that I overlooked. The particulars of what I have done and what I have observed/measured follow...

2016 Mercedes Sprinter Van Conversion
Cummins Onan LP 2500 Generator
2.5HGJBB-1121A (spec A)
Subaru X21 7HP Engine

This belongs to my friend, and he hasn't used the generator in quite a while and did not "exercise" it during that couple-year period. Now it won't start -- doesn't even try -- but cranks with no indication of any kind of problem. The blink code simply reports error code #4 which says that I've run the starter for 15-20 seconds with no result.

- The spark plug is clean and has a good blue/white spark. My assumption is that any of the sensor interlocks, such as the oil level sensor, would interrupt the electrical system and I wouldn't get a spark. But with a magneto -- which I think this has -- there may be no way of stopping the spark and they interrupt the fuel flow instead. I just don't know.
- The output of the two-stage regulator is 11" of water -- has been as high as 14" with no difference in the symptoms.
- The gas solenoid opens -- can hear the click -- and you can hear the sound of gas flowing when the start/stop switch is pushed to the Prime position.
- The LP Regulator works with no leaks -- pulled it, opened and examined, used a MityVac to put a small vacuum on the outlet and the diaphragm opened, allowing flow through the inlet. The LP regulator vent hose is clean and clear of obstructions.
- The throttle and choke assemblies move freely -- I've manually opened and closed each of them while cranking with no change.
- Air breather is new - have tried with it installed and without.
- There is no vacuum being pulled into the bottom of the mixer when the engine is cranking -- required for the LP regulator diaphragm to open the inlet valve.
- Cannot hear or feel the fuel solenoid open when the On/Off switch is in the Start position.

There are tons that I don't know about LP-fueled engines, but this seems to indicate that the problem is not directly related to the fuel system itself.

It acts like one or both valves are staying open, preventing the downstroke of the piston from pulling air in, and creating the necessary vacuum. Or that I'm getting air around the piston on the down stroke.

There was one other thing of note that appears to indicate a mechanical engine problem -- I forgot to put the oil cap back on before cranking it and it blew oil out with a pretty high pressure. The specs say that this engine uses "splash" lubrication so that may be normal but seemed pretty high pressure to me.

I'm gonna use an unlit propane torch to blow propane directly into the mixer while cranking and see what happens.

Also, I'm going to see if I can get a compression tester in -- there is practically no access to anything on this beast -- and prove/disprove this theory.

But in the meantime, I'm hoping some of you will read this and critique my troubleshooting and see if you agree with my "almost" conclusion regarding the engine itself being the failure point.

Thanks in advance,

Just a country boy from the cotton fields of Alabama trying to get by in the big city...

[MrWizard]

Nice to hear, nice to get the feedback on the situation

[Howard_Woodard]

Ok, the MG is starting instantly and pulling its load fine.

There were two problems, fuel flow, and a stuck intake valve. I think the leaking fuel line was the root cause. As it leaked more and more, it probably ran on the lean side and had incomplete combustion, causing the propane to form varnish on the backside of the valve and its stem, and finally, after a period of non-use, stuck.

I freed the valve up first, but it still wouldn't start. Then, using a manometer I determined that there was a big pressure drop from the outlet of the solenoid valve to the low-pressure demand regulator with nothing in between but one segment of fuel line. The connections looked old and brittle but spraying both ends produced no bubbles. Apparently, the sound we were hearing that we thought was just the priming flow was a leak. The leak was in the line and that first segment is inaccessible without dropping the generator and removing much of the enclosure. I couldn't mine that hose because Onan uses a type of hose clamp that could hold one of Elon Musk's starships tethered to the ground and there wasn't room for side cutters. I used a clothes hanger to thread a new piece of hose alongside the old hose and, wa la, end of the problem. The owner says it has never ever started so quickly and it didn't bog at all as loads were added.

Thanks to those of you who posted -- I appreciate the help.

Regards to all,

Howard

[MrWizard]

"There is no vacuum being pulled into the bottom of the mixer when the engine is cranking -- required for the LP regulator diaphragm to open the inlet valve."

Can you attach a manual Vacuum pump to that inlet and use it to operate the regulator diaphragm, maybe get lp to engine

[Howard_Woodard]

Update: I passed the info along too soon -- sorry.

What I said was correct, but the generator still will not start and run on its own. If you give it a good shot of starting fluid it starts but only runs momentarily, until the starting fluid is gone. I have eleven inches of water ahead of the fuel solenoid valve, eleven inches coming out of the valve, but only 7-8 inches at the inlet of the LP regulator -- that's curious because even though I can't see all the hose, I think it's just one uninterrupted segment that connects the solenoid valve and the LPR -- and nothing getting through the LPR. I can't account for the pressure drop.

While I can't detect a vacuum on the LP mixer fuel input or throttle body, I can feel the intake stroke at the spark plug hole and it's enough to operate the vacuum switch for the choke control.

It appears that the LPR diaphragm is doing its job of reducing the tension on the inlet valve but there isn't enough input pressure to overcome the remaining spring tension to open the inlet and allow fuel through. "It appears..."

I'm at a loss here. Is there something else between the fuel solenoid and where I see the hose connecting to the LPR inlet? Is it likely that the hose is leaking enough to account for the 3-4 inches of pressure drop? There are no bubbles around either connection and there is no sound of flowing gas or much of the smell of propane.

Tomorrow I'm going to use another hose to connect directly between the solenoid and the LPR but really, I'm just grasping at straws here.

Any insights or ideas? Thanks in advance.

[Howard_Woodard]

**Update** See the following post instead...

Just a sticky varnish on the intake valve stem had it stuck in the open position. Two shots of penetrating oil for about 15 minutes each and a couple of good raps on top of the valve spring with a hard rubber mallet and all is well now.

If it were fueled by gasoline, he could add a valve-cleaning additive to the tank. I think the only thing he can do with LP is to run it for a few minutes occasionally.

Thanks all for your help.

Howard

[ICamel]

Try spraying some starting fluid into the carb to see if it will start.

I have to do that with mine at the beginning of the season.

[bgum]

Pull spark plugs put some seafoam in cylinder and then replace plug and turn engine over for a instant and let it set for a day. You may just be lucky.

[Howard_Woodard]

Thanks. It'll be a few days before I get back to it but that's where my money is too.

I'll come back here and post when it's resolved.

[bgum]

Stuck valves.