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1977-78 Onan 4kw Fires Only When Holding Switch


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  #1  
Old 04-12-2018, 01:02:47 PM
wmrayt wmrayt is offline
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Default 1977-78 Onan 4kw Fires Only When Holding Switch

I have an Onan 4.0BFR1600B according to Cummins.
It will fire as long as the start switch is held.
The fuel tank is full.
I have grounded the oil sending unit will not fire at all then.
When I test the output of power it goes to around 15 v a/c while holding the start switch. I don't know what rpm this would be but probably no where near running speed.

The only manuals I have been able to find speak of testing pins on a control board but I have not been able to find any such and the manuals do not list a BFR model in them.

When I search this model number I can nothing.
It is a 4kw two cylinder.

Thanks
Ray
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Old 04-12-2018, 01:30:17 PM
Wayne 440 Wayne 440 is offline
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Default Re: 1977-78 Onan 4kw fires only when holding switch

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I have an Onan 4.0BFR1600B according to Cummins...When I search this model number I can nothing...
My advice- forget about "according to Cummins" and have a look at the rating plate for yourself. You will probably find that you have a 4.0BFAxxxxx. Then get the manual you need and go from there.
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Old 04-12-2018, 02:24:32 PM
len k len k is offline
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Default Re: 1977-78 Onan 4kw fires only when holding switch

Bunch of manuals in the link. After you're there, Press control F and search on BFA

http://www.twinslan.net/~n0nas/manuals/onan/
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Old 04-12-2018, 04:03:56 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

No such thing as a 4.0 BFR. Should be a 4.0 BF-1R/1600B. Cummins hasn't got a clue. Grounding the oil sender will kill the ignition. Stick with the guys here. We can help you. Most common thing was an open resistor. Get the manual and study it. It has the test you can do yourself. 900-0337 is the one you need. Don't get the power drawer model. That is a different system. There was a 4.0 BFA but manuals will be the same.
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Old 04-12-2018, 05:58:32 PM
YellowLister YellowLister is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

Probably the resistor like Billy said. what it does is send power (12vdc) to ignition and fuel pump after the gen set has started.. when holding the switch it is powered by the battery.

The resistor is what limits the voltage the the charge system.. it is usually under the gen end rear cover on top. and you will see a burned spot or it will look like it's been in the oven to long.. it happens over 40 or so years.. can be found online or onan parts may have one.. he is a sponsor here
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Old 04-12-2018, 07:27:58 PM
wmrayt wmrayt is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

I jumper-ed the fuel pump and it kept running. As far as a resistor, I can not find one. I found a physically large metal cased diode under the starter button case. The wire to the fuel pump goes under the starter button case and straight out to the coil.
Have a photo of diode but cant seem to be able to attach

---------- Post added at 06:22:53 PM ---------- Previous post was at 06:13:31 PM ----------

Ok I re-read the post and took the sheet metal wrap off the rear of the gen. Found a large resistor that Ohms out at 4.49M so it is not open.

---------- Post added at 06:27:58 PM ---------- Previous post was at 06:22:53 PM ----------

I get 15v dc on both ends of the resistor.
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Old 04-12-2018, 08:05:01 PM
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

K2 is worth checking out. You can get a new one at good auto parts house.
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Old 04-12-2018, 09:06:06 PM
wmrayt wmrayt is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

I can not read anything on the resistor nor does it have any bands.
What is it resistance is it supposed to be and at what rating?
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Old 04-12-2018, 09:37:22 PM
Wayne 440 Wayne 440 is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

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I can not read anything on the resistor nor does it have any bands.
What is it resistance is it supposed to be and at what rating?
Without knowing exactly which set you have, I can only guess.

Somewhere around 7.5 ohms/25W or so. Certainly much less than 4.49 Megohms.
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Old 04-13-2018, 11:59:47 AM
wmrayt wmrayt is offline
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Default Re: 1977-78 Onan 4kw Fires Only When Holding Switch

The only parts list I can find is for BFA 01-1986 document # 965-0222 and lists it as 3.4 ohm at 25 watts.
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