Onan propane rough, quits

[mcewena]

The generator will start but then fart and sputter for a couple of minutes then die. Then won’t start. Leave it for a few hours and it might or might not be ok. Seems more failure prone in the mornings but still in the 70’s early morning and today it turns over freely but won’t fire.

No code flashes, vent tube clear , new air filter, propane tank full.

Ideas?

[mcewena]

wolfe10 wrote:

I really doubt PSI to the on-generator regulator is a problem unless kinked line, tank valve mostly closed, etc.

Bounder suggested it might be the lines. I thought maybe a pressure gauge would help determine. I’d been thinking about a T for an external BBQ anyway, two birds….

[wolfe10]

mcewena wrote:
If I could McGiver a pressure gauge on to the last fitting before the genny what pressure should it read?

With the regulator on the generator, PSI before on-generator regulator will be tank PSI which varies quite a bit based on temperature and fuel (propane vs propane/butane vs butane). This is true for liquid tap and for high pressure vapor tap= before house regulator).

I really doubt PSI to the on-generator regulator is a problem unless kinked line, tank valve mostly closed, etc.

[mcewena]

bounder39zman wrote:
the 3.6KY LP Onan genny's can be a real handful to diagnose with the symptoms you describe. After checking all the basics (compresion, ignition, fuel from tank to genny), you may want to replace the LP hoses on your set, due to their age. I have done this to several sets that were brought to my shop with this problem, and it seemed to fix issues. the fuel pressures to and from LP regulators are very critical, and any deterioration of hoses can cause problems. if you have any "backfiring or popping back" through carb., make sure to check rocker arms and valve lash.

If I could McGiver a pressure gauge on to the last fitting before the genny what pressure should it read?

[mcewena]

Waiting for the heat to break and access to a motorcycle jack to lower the genny and it’s worked just fine every day. Not sure what to do now….

[bounder39zman]

the 3.6KY LP Onan genny's can be a real handful to diagnose with the symptoms you describe. After checking all the basics (compresion, ignition, fuel from tank to genny), you may want to replace the LP hoses on your set, due to their age. I have done this to several sets that were brought to my shop with this problem, and it seemed to fix issues. the fuel pressures to and from LP regulators are very critical, and any deterioration of hoses can cause problems. if you have any "backfiring or popping back" through carb., make sure to check rocker arms and valve lash.

[wolfe10]

Ya, at least on our 6.5, had to pull the generator to access the regulator.

I do not know access on yours.

Once out, should be easy to identify the regulator and find an overhaul kit.

The problem with ours was the orientation of this very good, widely used regulator-- laying on "its side". If installed vertically like in propane powered vehicles the longer hydrocarbon chain contaminants just pass on through and are burned. Installed horizontally, they just collect. Again, this is on the older series liquid LP Onans-- yours may be completely different.

[mcewena]

That type of kit is cheap enough to do on spec even if it wasn’t the problem if it wasn’t for the poor access. Closest Onan shop is 3 hrs away.

Fuel tap is open.

Thanks.

[wolfe10]

mcewena wrote:
It says LPV on the label (Onan 3.6kyfa26120L circa 2006) and has its own regulator and line off the tank separate from the other appliances.

Do regulators typically fail? It’s the easiest thing to swap next.

If this is a liquid LP (has a separate liquid tap on the tank), then, at least on the earlier Onan liquid LP generators, the on-generator regulator had a habit of clogging up with the longer hydrocarbon chain contaminants often found in propane. It formed a light-viscosity grease-like substance and clogged the regulator. Overhaul kits were available, but would depend on what regulator you have (likely made by some propane equipment oriented company, not Onan). For example, this is the kit for 1993 Onan liquid LP 6.5 KW: https://centuryfuelproducts.com/rk-j-2-repair-kit

No first hand experience with your model. I would ask a tech at an Onan dealer if your model could be experiencing the same issue.

If propane tank was just filled, you might confirm that the valve supplying the generator is indeed open (it should have been closed while refueling).

Again, this is AFTER confirming the basics as on any engine.

[mcewena]

nickthehunter wrote:
I could list about a hundred possibilities. Air, fuel, spark - if you could narrow it down to which one seems to be deficient at the generator itself (I.e,: saying the propane tank is full doesn’t mean the propane is getting in the generator cylinder) that would lead to better answers to your problem.
If all else fails, clean the carbon out of the exhaust muffler, and check the oil.

It has good spark and “some” fuel and compression. Although I was only able to infer by smell and feel as propane is witchcraft to me and the access to the plug is such that I was only able to get my thumb under the plug hole and not a compression gauge.

Oil is good and arrester clean out needs a functional engine to work.

[mcewena]

wolfe10 wrote:
Is this a liquid or vapor LP generator-- i.e. looking at the propane tank, it the port supplying the generator liquid or vapor?

What year/model?

It says LPV on the label (Onan 3.6kyfa26120L circa 2006) and has its own regulator and line off the tank separate from the other appliances.

Do regulators typically fail? It’s the easiest thing to swap next.

[wolfe10]

Is this a liquid or vapor LP generator-- i.e. looking at the propane tank, it the port supplying the generator liquid or vapor?

What year/model?

[nickthehunter]

I could list about a hundred possibilities. Air, fuel, spark - if you could narrow it down to which one seems to be deficient at the generator itself (I.e,: saying the propane tank is full doesn’t mean the propane is getting in the generator cylinder) that would lead to better answers to your problem.
If all else fails, clean the carbon out of the exhaust muffler, and check the oil.