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Onan: 4BGEF Spec G - does my Coil Resistance look OK?


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Old 04-09-2018, 09:30:28 AM
maillemaker maillemaker is offline
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Default Onan: 4BGEF Spec G - does my Coil Resistance look OK?

Hi all,

I have an Onan 4BGEF826101G generator in my 1990 Winnebago Warrior. Serial number is I900347047.

It will crank, but will not start. I purchased a spark tester - this is a small device with a light bulb that you put between the spark plug and its boot. The device works as I tested it on the RV engine. With the Onan generator, no spark is detected on the outbound-facing spark plug. I did not bother to check the inward-facing plug as it is hard to get to when the genset is in the RV.

I removed the coil and tested the primary (small terminals) and secondary (plug wire terminals) coil resistances using my ohm meter.

I am using this version of the Onan Service Manual:

https://rich.homeunix.com/gravely/en...t/965-0528.pdf

This is the page I am referring to regarding the Spec G generator:



First I tested the primary coil resistance:



It looks like the primary coil is good, measuring 3.6 Ohms. It should measure between 3.87 and 4.73 Ohms. It is a little under but this is probably OK.

Next I tested the secondary coil resistance:


I believe the secondary coil is good, measuring 17.4 K Ohms which is just a hair under-spec between 17.45 and 19.8 K Ohms.

Do you all agree with my measurements? I'm not an electrical person so I hope I'm using the meter correctly to measure resistance. I believe I had the meter in the correct range for the measurements.

So the next question is, why no spark? I think the only other thing that could be stopping me is the control board, which I will follow the service manual instructions for checking next weekend. I guess it could be the ignition control module, but it is said these seldom break.

Can the Voltage Regulator stop the spark?

Thanks,
Steve
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Old 04-09-2018, 10:31:24 AM
Kevin K Kevin K is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

The spec G BGE has electronic ignition. Before condemning the coil, perform the ignition module test on page 6-10. It is rare for a coil to go bad.

The most likely problem is rodent infestation. Mice have built a nest in the generator end, then when it was cranked one or both of the plastic arms holding a magnet has snapped off and the ignition module will not be triggered.
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Old 04-09-2018, 10:39:54 AM
armandh armandh is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

+1 on the expert advise above, and more generally.....

with the coil in place connected and the meter set just above the 12V DC

measure each low voltage terminal to the engine frame while cranking

one side will show the [more or less] 12V battery voltage
the other side should show alternately as the engine turns
12 VDC; points [either mechanical or electronic] are open
0 volts; points are closed to ground.

spark occurs when the points open
and the magnetic field in the coil collapses
the output HV coil is in series with both plugs
so all must be connected for either to spark.

if there is no 12 V at all there is a problem in the various safety systems
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Old 04-09-2018, 11:12:50 AM
maillemaker maillemaker is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

Quote:
with the coil in place connected and the meter set just above the 12V DC

measure each low voltage terminal to the engine frame while cranking

one side will show the [more or less] 12V battery voltage
the other side should show alternately as the engine turns
12 VDC; points [either mechanical or electronic] are open
0 volts; points are closed to ground.
OK, to be clear here, I am supposed to hook the voltmeter up to the primary coil inputs on the distributor and check for a voltage fluctuation between 0-12 VDC as the engine is cranking?

One of the terminals is bigger than the other. Which is the positive terminal?

Thanks for the replies,
Steve
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Old 04-09-2018, 03:39:55 PM
armandh armandh is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

I was referring to the threaded terminals

negative meter lead to the engine frame or battery minus

two tests
one checking for good 12 volts
one checking for point operation
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Old 04-09-2018, 04:17:09 PM
len k len k is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

Check spark while pushing start button.

Believe Only ONE spark when push it , then nothing till you release it , then ONE more spark as release it is typical for broken plastic arms.

If everything is good it should spark continuously while engine is cranking

Last edited by len k; 04-09-2018 at 05:00:11 PM.
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Old 04-09-2018, 04:52:03 PM
boomers influence boomers influence is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

steve
your P electronic ign coil SHOULD BE
2.9-3.6 on the primary
14,500-19,800 on the secondary.

thank you. boomer ( the used onan engine parts guy,also NOS and new )
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Old 04-09-2018, 08:21:44 PM
radiodoc radiodoc is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

Probably wouldn't hurt to check the spark plug cables to make sure both are good...Allie
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Old 04-10-2018, 08:31:54 AM
maillemaker maillemaker is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

Quote:
I was referring to the threaded terminals

negative meter lead to the engine frame or battery minus

two tests
one checking for good 12 volts
one checking for point operation
OK, I got it now. I should attach negative lead to engine frame, and positive lead to each of the threaded (primary coil) connections, one at a time.

One of them should give constant 12 volts, the other should alternate from 0-12 VDC.

Thanks for clarifying! I was going to attach the leads to both threaded connectors at the same time.

Quote:
your P electronic ign coil SHOULD BE
2.9-3.6 on the primary
14,500-19,800 on the secondary.
I'm measuring 3.6 on the primary, and 17,400 on the secondary, so it sounds like my coil is good. Thanks for the confirmation!

This weekend I will do the first test to confirm that the ignition module is functioning.

Where is the ignition module, anyway? I was hoping to visually look for the magnet arm.

Steve
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Old 04-10-2018, 11:37:29 AM
KPack KPack is offline
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Default Re: Onan: 4BGEF Spec G - does my coil resistance look OK?

Number 5 in the parts manual.
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