Onan 4000 generator cranks but won't start

[SJ-Chris]

Hi all,

I have a 2015 Cummins Onan RV QG 4000 generator. It has somewhere between 300-1000hrs (not sure, I've only owned it for about 2 years and it was a previous rental...might not be the original generator on this RV and I don't trust the hour meter coming from the rental company). About 1 year ago, I replaced the oil, air filter, and spark plug. Since then there has been 50-100 hours. Up until recently it has been working fine.

Recently, it won't start. It cranks and cranks very strong, but doesn't start.

To troubleshoot so far here is what I have done to no avail...
- I have a full tank of gas in the motorhome.
- The motorhome is level.
- Altitude adjustment set to 0 (I am near sea level).
- I checked the oil to make sure there wasn't too much (it is to the low end on the dipstick as most seem to recommend).
- I swapped in a good spark plug to make sure that wasn't the problem, and it didn't fix it.
- I checked the air filter and it seems fine (...even tried starting it without the air filter and it didn't start).
- I changed the fuel filter with a new one, primed it and tried starting it several times and that didn't fix the problem.
- I disconnected all the batteries (and my solar) per someone's suggestion to "reset" the generator. Hooked everything back up and it still didn't fix the problem.

It still cranks very strong...just doesn't start.

The only error code I could get from the lights was '4' (which is over-cranking). I don't think in all the testing that I did I ever let it crank for more than 10-20 seconds at a time.

I have reached the current extent of my generator knowledge! lol.... I'm hoping some of you can help me expand that knowledge with some more suggestions/recommendations.

One thing I've learned about owning an RV (...I actually have 3 now) is that it makes sense to try to learn to fix as much yourself as possible because RV mechanics are a)busy, b)expensive, and c)a hassle to drop off/pick up/etc. Plus, it's fun/satisfying when we can fix our own rigs and not be as dependent on others.

Thanks in advance!
Chris

[Gjac]

Thanks for letting us know the outcome, especially with such a great story and a happy ending.

[udidwht]

FYI....

For anyone in the Seattle area we have a great generator tech named Chuck. He's in Auburn, Wa. He agreed to come out to me (Renton-Highlands) and diagnose my Onan Microquiet 4K which would only run if I hold the start button.

I initially checked with a volt meter some pins and narrowed the issue down to either a bad control board or voltage regulator. When Chuck showed up he threw his Flight Systems G-Man 360 on it and within 5 min bingo...bad voltage regulator.

The voltage regulator that was on it had been replaced back in 7/11 with a Flight Systems 305. I was leaning at it being a bad control board.

So if you need a generator looked at call Chuck (253) 820-1388

[Eevie]

Ya, he's not as great as you think. He "fixed" ours, we went on vacation, it went out, and my other died of heat exhaustion on the way home. True fact.

[way2roll]

Not sure if you noticed but this topic is 3 years old. 

[Eevie]

Yep but the fact remains... Thx tho.

[enblethen]

Thanks for the positive results!

[SJ-Chris]

Update: Generator FIXED...here's what was wrong....

So my local RV mechanic had told me that the engine on the generator was done/broke and that it doesn't make sense to replace the engine on these Onan 4000 generators (...I've actually heard that from a couple of knowledgeable mechanics). My options were to buy a new one or a used one.

While investigating buying new, I learned that it would cost ~$4000 shipped for a new Onan 4000 generator (which I was okay with) BUT it would take somewhere between 10-29 weeks to deliver. There is a big parts/component shortage causing huge delays. I didn't like the idea of waiting. So I started looking for a used Onan 4000 generator. I quickly found out that there weren't really very many options. I found a couple locally, but the owners could never get back to me with answers to my basic questions and they seemed flakey.

Then I feel like I lucked out....I found a guy who is retired and now seems to have a passion for rebuilding/refurbishing RV generators. Sounds like he's done dozens and dozens of them over the last 10 years. Incredibly knowledgeable. He had an Onan 4000 that he just finished refurbishing that I could buy for $1700 that was fully tested and operating to spec (and he could demonstrate happily). He also offered to help install it into my RV with my help. I felt like I struck gold finding this guy and made arrangements to visit him (...he was a couple hundred miles away, but I could turn it into a mini-vacation and visit a friend of mine who happened to live nearby). He also insisted, "Let's take a quick look at your current non-running generator and see if we can fix it...that way you won't need to buy this refurbished one." You can tell a lot about the guy's character right there...he wasn't just trying to sell me his latest refurbished generator.

So I visited him on Monday. He asked me if I wanted to just drop it off, or if I was interested in learning more about these generators and I could troubleshoot it with him. He is a bit of an old-timer and I could see that he probably would enjoy some company. And, Since I'm always looking to learn, I stuck around. After about 2 hours he was able to identify what the problem was and he declared, "I can fix this generator for you!".

Here's what the problem was....(Please excuse me if I mis-name any components in my description...I'm not a mechanic)... Once he removed the carburetor he could see the throttle plate (flap) on the carburetor had broken free and was forced downstream and he thinks it might have been wedged in a way that was holding the valve open (hence no compression). We found the throttle plate lodged in that region. There are 2 screws that hold that plate on and they were missing (...presumably they went through the engine). We pulled the cylinder head/cover to inspect the piston and the chamber and you could see on the piston there were some marks/scuffs, but the chamber looked great with no damage. He said my carb looked beyond repair, but he had replacement/rebuilt carbs. He told me he was highly confident that he could quickly refurbish my generator, replace the carb, replace anything else needed while he was in there, do a valve job, etc. He is the kind of guy who could probably rebuild this generator with his eyes closed, AND he took great pride in his workmanship and wanted to make sure when he was done fixing the generator it would be at factor spec/tested and working as good as new (he had all necessary equipment/tools and then some). I left to visit with my friend, but he spent 10 hours working on it that day and the next and I came back the next afternoon and we tested it and reinstalled it. I helped out as much as I could with various aspects and enjoyed learning in the process. He even did a little welding on my support brackets because there was some rust that made him uncomfortable on the brackets and now they are super reinforced. Once installed, we tested it again and it is purring like a kitten even under full load.

I am confident this generator will last quite a while now. Out the door cost for parts and ~12 hours of labor: $780. I'm quite pleased!

Happy camping all!
Chris

[enblethen]

Like in many Briggs motors, genset has a decompression feature on the cam shaft gear. Failure of this device is common in some briggs.
Engine parts breadown

[Gary45]

Anyone who does lawn mower or garden tractor repair should be able to repair motor

[enblethen]

Look around your area for a small engine shop. Some will work on Onans. Problem is finding some parts. Shop may want you to get them!
RV shop is not the place to take it!

[SJ-Chris]

Update: I reached the end my my troubleshooting abilities, so I brought it to my local RV mechanic. After quickly testing that it wasn't something simple, he removed the generator from the RV so he could remove the cover and dive in deeper. Long story short...he tells me the motor is shot. He thinks it must have overheated and some of the internals went ka-put (....he rattled off some internal components that had broken/etc that I didn't jot down). He tried replacing one item and put it back together but was still getting zero compression. He says it would probably cost more money to try to fix this one and it is time for a new generator...

He recommended I find a good used one if I can find one with a warranty. I liked his recommendation as I felt like he wasn't just trying to gouge me for more $$$ and he wasn't pushing me to go out and get a brand new generator.

I wanted to get some opinions from those of you out there who care to share....

This RV is a 2015 Thor Majestic 28a. Previous Cruise America rental. I've been very pleased with it so far (and I have another identical one). They serve well for how I am using them. This one has 140,000 miles on the engine. I can easily see holding on to this one for another 3-5 years. Everything else seems to be in good shape. Would you buy a brand new Onan 4000 generator and install it? Would you go for a used one for less than 1/2 the price?

I did some googling. There are two used ones locally each for ~$800. If I'm going to buy used, I will require seeing that it runs.

I also found these new ones...
https://www.norwall.com/products/Cummins-Onan-QG-4-0-EVAP-Gasoline-RV-Generator-40KYFA-6747/?ctm=onan&gclid=CjwKCAjwmK6IBhBqEiwAocMc8pMmjQtGLnbkDF-LjmWtIROKeqAOqJSwPhQdLswWpNlLwdpZYoLZzxoCXDkQAvD_BwE

https://www.norwall.com/products/Cummins-Onan-QG-4-0-EVAP-Gasoline-RV-Generator-40KYFA-6747/?ctm=onan&gclid=CjwKCAjwmK6IBhBqEiwAocMc8pMmjQtGLnbkDF-LjmWtIROKeqAOqJSwPhQdLswWpNlLwdpZYoLZzxoCXDkQAvD_BwE

and I'm sure I can find others. Seem like new ones cost ~$3300-3500.

Does anyone know of any companies out there who rebuild/refurbish Onan generators and sell them with warranties?

I'm not opposed to buying a brand new one. Just weighing my options and looking for opinions (which often times can be valuable and lead to discovery of additional options).

Thanks in advance!
Chris

[SJ-Chris]

Gjac wrote:
How are you making out with your genset?

I was out of town (not RVing) for the last 7 days. I will continue working on it this coming week.

-Chris

[Gjac]

How are you making out with your genset?

[Gjac]

enblethen wrote:
I am guessing the "compression tester" screwed into spark plug hole.
Sounds like it could be a stuck valve in open position. Most likely an exhaust valve.

I agree with Bud, try the compression tester on your lawn mower and see what it reads, if zero and mower runs fine there is some thing wrong with your tester. How many hrs on your genset?