Onan 4000

[dktool]

I am on a trip and my Onan 4000 will fire and try to run as long as the start switch is maintained in the cranking position.
What does this run circuit look for besides oil pressure and does it even look for that until it has achieved a start ?

Are these known for circuit board failure that would cause this condition or ??

Thanks in advance for any tips.

 

[DonTom]

I am on a trip and my Onan 4000 will fire and try to run as long as the start switch is maintained in the cranking position.
What does this run circuit look for besides oil pressure and does it even look for that until it has achieved a start ?

Are these known for circuit board failure that would cause this condition or ??

Thanks in advance for any tips.

That means the control board is shutting it down for a reason. It cannot shut down until you let go. Since your genny must be in a 1993 rig, I am not sure if it has the codes or not. The older gennys don't have the feature.

Use the start switch on the genny itself. It has a red light. After you try to use it and it dies when you let go, you will most likely get three blinks of that light. That means you have a two-digit code stored. To get that code, press one time fast to the left on that same switch (prime), It will blink a two-digit code. Say it blinks once and then four times. It will repeat that several times so you it is okay if you miss the first code. That will be an error code of 14. After it blinks several times with that 14 (or whatever code you get) you may or may not get another code. So get that two-digit code and post it here. If more than one post those here also.

And see here. Code 14 means it is running too fast, making the frequency too high, so it will shut down before it damages anything or cause things not to work properly. It must run very close to 3,600 RPMS cold or hot. Code 15 is too slow, etc.

-Don- DeRidder, LA

 

[dktool]

My unit does not have any indicator pilot light or a prime function.
It is original in my 1993 built Flair.
Also this is the old school twin cylinder low rpm type, not the 3600 rpm model.

(this model)

 

[DonTom]

My unit does not have any indicator pilot light or a prime function.
It is original in my 1993 built Flair.

That's a bummer!

The first step will be to get all the digits of the generator model number from the genny itself. Perhaps is around a dozen digits.

Then search for the manual for that model number. Onan is great about putting their manuals on the web.

-Don- DeRidder, LA

 

[LarsMac]

What level is the fuel on your vehicle?
That is the first "gotcha" that should be ticked off the list.
If you're under a 1/4 tank, the genny may not start.

 

[NY_Dutch]

I am on a trip and my Onan 4000 will fire and try to run as long as the start switch is maintained in the cranking position.
What does this run circuit look for besides oil pressure and does it even look for that until it has achieved a start ?

Are these known for circuit board failure that would cause this condition or ??

Thanks in advance for any tips.

A common cause of this condition occurs if the generator is not putting out enough voltage to lock in the run circuit on the controller. And a common cause of low output voltage is tarnish buildup on the copper slip rings or worn brushes. In a 1993 RV, you most likely have a 4BGE model generator that does not display error codes. If your generator is similar to the one pictured below, Flight Systems, Inc has a tool that makes cleaning the slip rings fairly easy. There's also a video showing how it's used. The photo shows an Onan BGE 5000, but the 4000 looks pretty much the same.

https://www.flightsystems.com/56-a360-09-slick-stick.html

 

[Isaac-1]

I tend to agree with NYDutch here, How long has it been since it last ran? Tarnish build up due to disuse leading to voltage regulator failure is a common problem of Onan generators from this era.

 

[dktool]

It hadn't been run for about 3 months, I used it for short runs 4 times in the past 2 days (coffee, toaster,microwave) the first start after sitting 3 months was normal, crank until the carb filled then fired up. Yesterday had one stubborn start event then 2 normal ones, today had 1 stubborn, 1 normal and then the described non starting.

The fuel supply level is well above 1/4 and it is obvious the carb has fuel.

The slip ring low or non voltage to lock in the run circuit makes sense, anything else come to mind anyone ?

 

[dktool]

The Slick Stick would be slick to polish the slip rings if the engine was running, but .......

 

[dktool]

Tarnish build up due to disuse leading to voltage regulator failure is a common problem of Onan generators from this era.

Is that failure as in the regulator needing replacement or failure is in non function due to other component issues ? (ie slip rings)

 

[DonTom]

The Slick Stick would be slick to polish the slip rings if the engine was running, but .......

Use it while it is cranking. Shouldn't need the full RPM of the engine. But you can do it again if you get it started.

Probably will be easier as a two-man job. But there are tricks you should be able to do such as short out the relay contacts to keep it cranking with the spark plugs removed while using the Slick Stick. That should speed it up as well as make it a one-man job.

-Don- DeRidder, LA

 

[Lou Schneider]

You said the engine will try to run while the start switch is held down. Do you mean it fires and then quits when you release the start switch? If so, there's no harm in keeping the start button engaged for the 10 seconds or so it takes to use the Slick Stick after the engine starts. The starter has an overrunning clutch that lets it essentially freewheel if it's not actually cranking the engine.

 

[Isaac-1]

It can be either way, what typically happens is tarnish builds up which increases the resistance of the connection, then voltage regulator goes to full output and burns out. Though a lot depends on the dynamics of the given situation, ie some build up of tarnish, but still runs and outputs AC power tends to result in the voltage regulator burning out. Alternatively you may have a long term storage situation where a lot of tarnish builds up, then there is no AC output and the voltage regulator never tries to run long enough to burn out.

This of course is speaking in generalities, and does not address your specific revision of the BGE

 

[dktool]

You said the engine will try to run while the start switch is held down. Do you mean it fires and then quits when you release the start switch? If so, there's no harm in keeping the start button engaged for the 10 seconds or so it takes to use the Slick Stick after the engine starts. The starter has an overrunning clutch that lets it essentially freewheel if it's not actually cranking the engine.

It does try to stay running when the start switch is held on and the starter bendix is bouncing in and out, free wheeling and doing the tooth dance with the flywheel.

I'll take a look in at the slip rings if possible and see if they're obviously discolored.
Hopefully that's the problem and voltage regulator didn't kill itself.

In lieu of the slick stick would contact cleaner or ?? work to get it going while waiting for a slick stick to arrive ?

 

[Mark_K5LXP]

Seems the successful "short runs" of the previous days would've cleaned up the slip rings. Seems odd that this would happen after the genset has just worked OK. My first stab at it would be to monitor voltage and frequency while the start button is held and see if that indicates anything. Don't the older Onan's also have an oil level switch? Agree with DonTom and dig up some service information on the intertubes, which will have some troubleshooting steps.

Mark B.
Albuquerque, NM

 

[NY_Dutch]

Do you have a volt meter you use to check the output voltage while it's cranking?

 

[Kirk]

It does try to stay running when the start switch is held on and the starter bendix is bouncing in and out, free wheeling and doing the tooth dance with the flywheel.

Onan is designed such that the engine uses voltage from the starting battery as long as the start switch is held down but gets it from the generator output as soon as you release the start switch. Your symptom says that there is no voltage from the generator and sliprings could be the cause so do the easy things first.

 

[dktool]

I do have a multimeter and the skills to troubleshoot / repair with some pointing in the right direction.
If the run circuit is self excited by the stator via the voltage regulator which sounds like also takes care of the rectifying then all roads seem to lead back to the slip rings as a start point then to the regulator.

Unless...there is an oil level or temp switch that is faulty or an issue with the circuit board not doing the logic connection to the run circuit ??
This is my unit;

 

[dktool]

I was able to look at the slip rings, they are definitely tarnished.
I would like to check the resistance as is for a baseline reference before cleaning.

Is the rubber'ish pop in cover under / near the air filter cover meant to be an access point for cleaning or something else ?

 

[Isaac-1]

If you don't have it yet, here is a link to the service manual for your generator, yours is Spec Code J (revision) as can be seen by the last letter in the model number 965-0528 Onan BGE (spec F-K) NHE E-K) Genset Service Manual (09-1994) 965-1060 Supplement M) (11-1995)

Testing procedures and resistance specs should be in there, though note that multimeters do a poor job of accurately measuring very low resistances, traditionally a wheatstone bridge is used