ONAN KV 2500, WON’T CRANK

[patgearty]

CONFIGURATION
ONAN 2500 Watt GenSet – LP fuel - Microlite 2800 Series
Model 2.5KV FA26120K, S/N: K030571650
Motorhome: 2004 Leisure Travel, 210 B, 2003 Mercedes Sprinter, 250k miles
20-year-old generator has 300 hours on it. Mounted below.
I’ve owned, operated, and maintained it for 15 years. Routinely Exercised. Oil, sparkplug, filter, good.
ISSUE
Will not start. Attempts to start are the same using either the remote Start switch or the one on the generator. Start button results are no crank or clicking. This has been an intermittent issue for the last two years. When it does start it runs fine. I tried to relate it to level issues, time, weather, motion, periods of use or idle and never found any correlation. On a recent trip it started and worked well several times, then failed to start. Two weeks have now passed and repeated attempts to start result with no cranking.
Mounted under the Sprinter makes it very difficult to analyze. Dropping it out is way beyond my ability. All the 12-v systems in the motorhome are working and in good condition. All the underside cabling to the generator looks clean and good. I’ve tried to determine if 12v DC is getting to the generator. The 12-v cable is housed in a conduit so I can’t get a probe to it to test for voltage. The 12-v supply cable originates in the motorhome where I can access it. That connection is clean, solid and a test probe into the cable shows good 12 v supply voltage. The 5-amp fuse in the generator was good but I replaced it with a new one to make sure it is good. I made a test connection into the 5-amp fuse holder and did not see 12-v there. (12v references includes tests at actual 13.5 v.)
Twice I measured for voltage on the remote switch start wire and found it at 11.5v. As soon as I pressed Start (no crank) and released the voltage went to 0 v. It appears that there is some weak component in the start circuit path that produced this.
WHAT NOW?
My coach battery is a 100AH AGM that serves me well. We most often travel part of the day, so the engine alternator usually recharges us, and I have some solar. I have considered converting to lithium but do not want to do that. As indicated by the 300 hours on the generator, not much use in 20 years. I could live without the generator, but I like to keep this motorhome healthy.
I prefer DIY if not to fix at least to diagnose it. I haven’t been able to do either with this issue. It looks like I will have to take it in for service, Cummins/Onan most likely. If I do take it in, the labor cost to drop and analyze it will be considerable even if the repair is simple. And then what would its future be? I am considering replacing the KV with the new Onan QG 2500i LP. I know it’s a huge cost but would be reliable for years to come, I assume.
So, what to do? I am looking for insight into the issue and guidance on how to proceed. The resources on this forum are amazing and I will be grateful for your assistance.
Thanks,
Pat, Minneapolis, MN

 

[wmgeorge]

I do not know what meter your using or if you know how? First a fully charged 12 volt lead acid battery should read at least 12.6 volts, higher is better. AGM same but higher, Grounds near the battery to frame and engine should be cleaned and shiny, looking does not count.... same for all the positive hot wire connections. What your describing is a poor or loose connection... someplace and yes the battery voltage. Basics first. As a electrician for the past 60 years I can tell you start with the simple stuff first.
If this all checks out then its on to the more detailed stuff.

 

[patgearty]

I do not know what meter your using or if you know how? First a fully charged 12 volt lead acid battery should read at least 12.6 volts, higher is better. AGM same but higher, Grounds near the battery to frame and engine should be cleaned and shiny, looking does not count.... same for all the positive hot wire connections. What your describing is a poor or loose connection... someplace and yes the battery voltage. Basics first. As a electrician for the past 60 years I can tell you start with the simple stuff first.
If this all checks out then its on to the more detailed stuff.

 

[patgearty]

I appreciate your insight and advice. I concur, start with the basic things. Meters used are a Fluke 77 and a Simpson 260. Voltages were 12.6 and higher. I tested with the Sprinter engine & alternator running with 13.5 v supplied to ensure I had maximum power available. The Onan uses the coach battery and all connections were removed, cleaned and tightly secured. When attempting start, there is no dimming of the 12 v lights in the MH indicating that coach battery and connections are good. I suspect the issue is internal to the Onan which I cannot access.
Thanks, Pat

 

[wmgeorge]

Gee I haven't even seen a 260 for years, dumped mine when I started troubleshooting electronics. You now need a wiring diagram of your unit. Go to the Onan website or my RT came with books that had mine.
FYI it could still be a bad connection somewhere in that circuit you did not access?
Can you get the cover off the genset?

 

[wmgeorge]

PS I am 80+ I put a heavy duty floor jack under the hitch receiver and raised the frame 3 inches or so and got to the 2800, pulled the cover and checked the oil.. I gave my old still working fine Fluke 77 away when I purchased my new one. I carry the clamp on version in my 210. Good luck with your troubleshooting!

 

[Blueboy1]

Hi, just my small piece of experience but Onan generator starts and stop by grounding, meaning that 0 V is normal reading on either start or stop side of the switch. The common terminal on the start switch should be grounded, the start action actually serves as a grounding path to a small relay . If the stop action is working normally I suggest a loose terminal on the start relay , and it should be located in some kind of small panel box. Problem could be related to normal traveling vibrations.

 

[patgearty]

Hi, just my small piece of experience but Onan generator starts and stop by grounding, meaning that 0 V is normal reading on either start or stop side of the switch. The common terminal on the start switch should be grounded, the start action actually serves as a grounding path to a small relay . If the stop action is working normally I suggest a loose terminal on the start relay , and it should be located in some kind of small panel box. Problem could be related to normal traveling vibrations.

 

[patgearty]

As you state, I thought the start side would come from a relay to be grounded. That said, I would expect to see about 12 v on the start wire coming through the relay coil until grounded. Regardless, I can't get at the components as the generator is mounted under the RV and its beyond my ability to remove it.
Thanks, Pat

 

[InterBlog]

OP, your description of the electrical side of things is thorough, but I am a bit unclear regarding the maintenance history on your 20-year-old generator (other than the routine external tasks which you do mention).

The intermittent symptoms you describe are consistent with a failing internal propane regulator. Many people do not know (and it does not make intuitive sense) that there are typically two of them - there is usually an external one near the tank, a Camco or similar common model and those are well-known failure points (easy to replace when failed because they are external). But there is a second one inside the genset itself. It’s a flexible membrane and it’s unlikely that it would make it to 20 years without losing structural integrity. If you have not previously replaced that component during regular generator maintenance, it might be the source of your difficulties.

Onan (Cummins) actually sells prepackaged maintenance kits for exactly this reason. Unfortunately replacing it requires dropping the unit for bench work. It’s not that expensive if you know exactly what scope of work to ask for such that your repair guy does not have to waste a lot of time chasing his or her tail trying to figure stuff out. I had mine replaced by a small engine guy whose bread and butter work is fixing lawn mowers - this work does not require megabucks mechanics such as you will find at Cummins. You can read all about my journey in this thread below, where I’ve picked up the conversation starting at post #30:

2017 Airstream Interstate Onan Generator won't start - Page 2 - Airstream Forums

FINAL VERDICT: Generator is fixed and back in. Runs like a champ. The generator repair people replaced the cracked Onan hoses inside the generator with LPG hose. Cost - $130 part + labor. I had to

www.airforums.com

 

[wmgeorge]

As you state, I thought the start side would come from a relay to be grounded. That said, I would expect to see about 12 v on the start wire coming through the relay coil until grounded. Regardless, I can't get at the components as the generator is mounted under the RV and its beyond my ability to remove it.
Thanks, Pat

After looking over the diagram and reading the service manual I think either the relay contacts on K1 the start contactor relay are bad Or the starter motor is. (This is assuming you have checked at S1 for the 12 volts on the open switch wire as you posted above.) But neither of those parts are accessible when the genset is installed. So it needs to go to a Onan service center.
Taking to the Onan place will cost $500 or more so be really sure you have covered all the easy DIY fixes.
BTW I downloaded the service and repair manual right from Onan's website last night.

What InterBlog posted above also!!

 

[InterBlog]

P.S. on what I said in post 10 above - the linked Airforums thread meanders, as many forum threads do, so stick with it to get to the meat of the solution. Some owners found age-cracked hoses instead of an age-cracked internal regulator. I based my speculation on the age of the OP’s generator - similar to mine. Counterintuitively, it seems some younger generators are having hose issues instead of regulator issues.

 

[booster]

If the engine does spin on the starter, how can the propane regulator cause that?

Does it require a propane pressure sensor OK just the spin the engine?

 

[patgearty]

OP, your description of the electrical side of things is thorough, but I am a bit unclear regarding the maintenance history on your 20-year-old generator (other than the routine external tasks which you do mention).

The intermittent symptoms you describe are consistent with a failing internal propane regulator. Many people do not know (and it does not make intuitive sense) that there are typically two of them - there is usually an external one near the tank, a Camco or similar common model and those are well-known failure points (easy to replace when failed because they are external). But there is a second one inside the genset itself. It’s a flexible membrane and it’s unlikely that it would make it to 20 years without losing structural integrity. If you have not previously replaced that component during regular generator maintenance, it might be the source of your difficulties.

Onan (Cummins) actually sells prepackaged maintenance kits for exactly this reason. Unfortunately replacing it requires dropping the unit for bench work. It’s not that expensive if you know exactly what scope of work to ask for such that your repair guy does not have to waste a lot of time chasing his or her tail trying to figure stuff out. I had mine replaced by a small engine guy whose bread and butter work is fixing lawn mowers - this work does not require megabucks mechanics such as you will find at Cummins. You can read all about my journey in this thread below, where I’ve picked up the conversation starting at post #30:

2017 Airstream Interstate Onan Generator won't start - Page 2 - Airstream Forums

FINAL VERDICT: Generator is fixed and back in. Runs like a champ. The generator repair people replaced the cracked Onan hoses inside the generator with LPG hose. Cost - $130 part + labor. I had to

www.airforums.com

 

[patgearty]

Yes, 20 years of maintenance was limited to what’s accessible through the panel door: oil, filter and sparkplug. Quite impressive that the Onan served for 20 years and 250,000 miles on some pretty rough backroads without having to be removed and opened for service.
I appreciate your information on a failing propane regulator. My generator will not crank. Would a failed propane regulator result in no crank?

My thanks to all who have responded with advice. With that, I have concluded that the generator will need to dropped and that is beyond my abilities. So, it will be taken to a service provider for resolution.
Thanks all,
Pat