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Onan 4.0 BFA-1r16004c - Stops when I release START switch


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  #1  
Old 08-22-2017, 04:36:01 PM
ErikTande ErikTande is offline
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Default Onan 4.0 BFA-1r16004c - Stops when I release START switch

Was working fine, problem just started yesterday. It also ocassionally doesn't want to start at all (sometimes I press the switch and get nothing). So I assume the switch is bad. I searched and found a lot of older threads with the same issue.

It's all original so I figure I'll just order all new control parts to avoid issues in the future.

What's the best place to order the switch, resistor and start relay?
The old threads had broken links.

Thanks!!!
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Old 08-22-2017, 05:17:20 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

Hold up now do not start throwing parts into it most of the time when an onan will not start or stop running when we let off on the start switch they are not making power so could be brushes or the charge resistor for the 12 volt battery any how post the serial number and some one will be along and give you a hand me I am kind of rusty on the onans but I am sure they will help you trouble shoot it. Luck Onan Dan
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Old 08-22-2017, 05:23:06 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

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Originally Posted by Onan Dan View Post
Hold up now do not start throwing parts into it most of the time when an onan will not start or stop running when we let off on the start switch they are not making power so could be brushes or the charge resistor for the 12 volt battery any how post the serial number and some one will be along and give you a hand me I am kind of rusty on the onans but I am sure they will help you trouble shoot it. Luck Onan Dan

I can run the roof AC while holding the start button so it's definitely making power.

Is the serial number different than the model number in the thread title?
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Old 08-22-2017, 06:23:48 PM
gnucklehead gnucklehead is offline
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

I'm fairly certain that the BFA does not have the electronic voltage regulator, so dirty slip rings won't cause that symptom. Wiring diagram should be 611-1146, which I'll find a link for, or upload it again. You posted the model/spec#, the serial number is not there..

---------- Post added at 06:23:48 PM ---------- Previous post was at 06:16:03 PM ----------

Likely suspect is the low oil pressure sensor keeping K3 (run relay) from energizing. Maybe bad K3 or something else preventing it from energizing.

My NH uses the same controls Not a good idea to start it with the load connected, tho

Last edited by gnucklehead; 08-22-2017 at 06:38:12 PM. Reason: Got my Onans mixed up
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Old 08-22-2017, 06:27:23 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

The serial number will be some thing like B84355676.

First of all stop holding the start button and running the AC. You stand a good chance of burning up the system. The run relay can be bought at any auto parts store. Just a Bosch relay. The control resistor is back by the cooling fan if it is open it will cause your problem. Also look in the bottom of the control box for loose screws. That control box had a bad habit of screws coming loose and falling into the bottom. Shorting out the relays

Go to the twinslan section of this site. Down load the service manual.
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Old 08-22-2017, 06:57:27 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

Your service manual is here. Onandan made me laugh when he said hold up he sounded serious.
http://www.twinslan.net/~n0nas/manuals/onan/
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Old 08-22-2017, 07:02:06 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

Quote:
Originally Posted by Billy J Shafer View Post
The serial number will be some thing like B84355676.

First of all stop holding the start button and running the AC. You stand a good chance of burning up the system. The run relay can be bought at any auto parts store. Just a Bosch relay. The control resistor is back by the cooling fan if it is open it will cause your problem. Also look in the bottom of the control box for loose screws. That control box had a bad habit of screws coming loose and falling into the bottom. Shorting out the relays

Go to the twinslan section of this site. Down load the service manual.
Billy when your wife gets to hot you got to run the ac even if you have to set there and hold the start button.
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Old 08-22-2017, 09:20:26 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

KPack. Just rent her a hotel room.


I knew a guy out near Coleman. Wife didn't like having a generator around the house. One day a transformer blew out. Killed power all over the county. She changed her mind when the generator started and the AC came back on. Nothing like a good Texas July day to change peoples mind.
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Old 08-22-2017, 10:09:15 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

that's true Billy, my wife grumbles about all the junk I got until they start talking hurricanes and she tells me get the generator ready.
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Old 08-22-2017, 10:13:58 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

We never used to lose power for more than ~hour or so when someone hit a utility pole, except for ~ 1967

For me I got into gens when we had a 18 hour outage in winter and dad kept saying it's cold, put the heat up, and I couldn't , no electricity
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Old 08-23-2017, 12:01:30 PM
len k len k is offline
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

In general Onan used 2 relays to power the spark coil and fuel pump. Looking at schematic it's K2 and K3.

One relay K2 would power them while holding start switch to start engine.
The other K3 would continue powering them after you released start switch, if oil pressure was up.

Possible a relay contact is dirty, these were open relays, not sealed

Odd but from schematic looks like this gen does check to see engine is turning. It uses back EMF from starter windings to power K3

Last edited by len k; 08-23-2017 at 12:21:05 PM.
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Old 08-25-2017, 04:35:40 PM
ErikTande ErikTande is offline
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

Quote:
Originally Posted by Billy J Shafer View Post
The serial number will be some thing like B84355676.

First of all stop holding the start button and running the AC. You stand a good chance of burning up the system. The run relay can be bought at any auto parts store. Just a Bosch relay. The control resistor is back by the cooling fan if it is open it will cause your problem. Also look in the bottom of the control box for loose screws. That control box had a bad habit of screws coming loose and falling into the bottom. Shorting out the relays

Go to the twinslan section of this site. Down load the service manual.
Oh come on, you don't really think I'm holding the start butting and running the AC do you? : P

I make the wife do that. ; )


Onan Dan said it could be that the generator isn't making power, I was just pointing out that it does.

Combined with the fact that sometimes the start button does NOTHING it all, what could it be other than the start button? The relay? My point is, why not order both so I have backups on hand?

Could it be anything other than those 2?

Thanks again!
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Old 08-26-2017, 05:11:27 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

1. Resistor R1 may be open
2. Run Ignition Relay K3
3. Low Oil Level
4. S3 Low Oil Pressure Switch may be defective

Or a bad connection or broken wire can cause the same symptom.

BFA (Spec C) Operator's manual (965-0122) has a controls troubleshooting guide
http://www.twinslan.net/~n0nas/manua...0(04-1981).pdf
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Old 08-26-2017, 06:21:36 PM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

My Uncles 4.0BFA acted the same way it would turn over and run long as one held the start switch it was the start run relay in control box I had a used pair of relays and replaced them both and took care of the issue.
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Old 09-12-2017, 12:28:06 AM
ErikTande ErikTande is offline
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

I did a little more troubleshooting (very little) and in the first post I mentioned that sometimes when I press the start switch I get nothing at all. Well now it's not sometimes, it's all the time. Switch does nothing, neither the switch on the generator or the remote start switch in the cab. Knowing that, it's probably not the switch that's the problem, right? Oil level is fine.

So it could be the run relay. (just a bosch relay?) I have one laying around so I'll try swap that first.

From there it could be the resistor or the S3 Low Oil Pressure Switch, right?

Thanks!

Oh, and I took the motorhome racing at Bandimere speedway. Any guesses what it ran?


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Old 09-12-2017, 07:08:51 AM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

I've got a parts unit here if you need something. No guess on the mh
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Old 09-12-2017, 11:59:09 AM
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Default Re: Onan 4.0 BFA-1r16004c - Stops when I release START switch

AS a test I'ld disconnect remote start/stop switch from gen , at the gen. That way your only testing gen, not RV wiring. Shorts in RV wiring can cause problems.
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