Onan genset 4.0 no spark. Help

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PigCreations

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Thanks DonTom for the reply. When it was tested, the gen was out of the RV and had no load on it. Finally had the chance to look at it today. Didnt start it but noticed a thick oil residue on the copper bindings. Could this be causing the wires on the stator to be getting too hot?
 

DonTom

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. Didnt start it but noticed a thick oil residue on the copper bindings. Could this be causing the wires on the stator to be getting too hot?
Can you take a photo of it and post it here?

But what I am thinking is that you have shorted out stator windings. Sometimes we can tell just by looking.

For an example, here is a stator I removed last April from my 1984 Venture motorcycle shown on the right. Would not charge at all. The used good replacement is on the left.

One look and I had no need to even test the stator on the right. Bike now charges like new with the stator sown on the left. Should be good for another 37 years, unlike me, unless I make it until I am 109 years old.

-Don- Reno, NV
Stator.JPG
 

DonTom

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Here is a couple pics of the stator. The windings look a little dark but not as "burnt" as your stator.
Yes, I agree, nothing obvious there by looking. If you have the specs of the resistance on the coil and an ohmmeter that can check very low resistance, it's one way to be more sure. Probably a fraction of an ohm is normal for the windings and also make sure no shorts to ground from the coil.

-Don- Reno, NV
 

PigCreations

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Riverdale California
sorry for the delay, losing motivation as I am frustrated with this thing. I have it back in the motorhome, it will not turn over, nothing happens when I try to start it. Did notice the resistor on the stator (#14 in the attached pic) gets super hot has soon as I connect the battery. Wondering if the rectifier/diode (#33 in second attached pic) could be the problem. Is that rectifier/diode directional or is it just bad?
 

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DonTom

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Is that rectifier/diode directional or is it just bad?
Diodes will switch off with the opposite polarity of what turns them on. But your voltmeter has to have enough voltage to turn it on and if it's a high voltage diode it may not turn on from the low battery voltage in the ohmmeter. A normal silicon diode drops 0.7VDC, but high voltage diodes are made from many diodes in series in the same package, so of there are ten diodes in series internally, then it needs at least seven volts to read that one HV diode package.

That resistor looks like a high wattage wire round resistor. It will get quite hot in normal operation. Too hot to touch will be the norm there.

-Don- Reno, NV
 

Bdon42001

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Arizona
sorry for the delay, losing motivation as I am frustrated with this thing. I have it back in the motorhome, it will not turn over, nothing happens when I try to start it. Did notice the resistor on the stator (#14 in the attached pic) gets super hot has soon as I connect the battery. Wondering if the rectifier/diode (#33 in second attached pic) could be the problem. Is that rectifier/diode directional or is it just bad?
Good afternoon, where did you find the diagrams posted? I just purchased an 84 motorhome with a 4.0 Genset and it only has 23 hours on it. It looks like it was hardly ever used and it will not crank. I feel like some of the wiring may be hooked up wrong. I replaced the solenoid and it still does nothing.
 

Henry J Fate

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Probably good to start with the service manual. You will need the model# and the serial#. I prefer to go direct to Cummins Sales and Service 800-286-6467 but it is possible to get the service manual from other sources using google. If you call Cummins, they will usually send a FREE copy of the specific service manual to an email address.

The age of the generator would be of a high concern. I would first make sure that the engine is turning freely. I cannot say exactly how to manually confirm this on your model, but it would be best to first figure out how and check the motor. After that it would probably come down to the starting circuit and components of. The starter is obviously on the top of the list since you replaced the solenoid. You can check the solenoid for proper operation with a multi-meter.

You will also need good and charged batteries to start the generator. I would make sure the batteries are fully charged as there will be extra power needed to turn over a generator that's been sitting for a few decades. Usually, the generator is wired to the house batteries but you should verify this, so you know where the power is coming from.

What exactly are the symptoms when you push the start button ? What do you hear or see ?
 
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Bdon42001

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Probably good to start with the service manual. You will need the model# and the serial#. I prefer to go direct to Cummins Sales and Service 800-286-6467 but it is possible to get the service manual from other sources using google. If you call Cummins, they will usually send a FREE copy of the specific service manual to an email address.

The age of the generator would be of a high concern. I would first make sure that the engine is turning freely. I cannot say exactly how to manually confirm this on your model, but it would be best to first figure out how and check the motor. After that it would probably come down to the starting circuit and components of. The starter is obviously on the top of the list since you replaced the solenoid. You can check the solenoid for proper operation with a multi-meter.

You will also need good and charged batteries to start the generator. I would make sure the batteries are fully charged as there will be extra power needed to turn over a generator that's been sitting for a few decades. Usually, the generator is wired to the house batteries but you should verify this, so you know where the power is coming from.

What exactly are the symptoms when you push the start button ? What do you hear or see ?
Probably good to start with the service manual. You will need the model# and the serial#. I prefer to go direct to Cummins Sales and Service 800-286-6467 but it is possible to get the service manual from other sources using google. If you call Cummins, they will usually send a FREE copy of the specific service manual to an email address.

The age of the generator would be of a high concern. I would first make sure that the engine is turning freely. I cannot say exactly how to manually confirm this on your model, but it would be best to first figure out how and check the motor. After that it would probably come down to the starting circuit and components of. The starter is obviously on the top of the list since you replaced the solenoid. You can check the solenoid for proper operation with a multi-meter.

You will also need good and charged batteries to start the generator. I would make sure the batteries are fully charged as there will be extra power needed to turn over a generator that's been sitting for a few decades. Usually, the generator is wired to the house batteries but you should verify this, so you know where the power is coming from.

What exactly are the symptoms when you push the start button ? What do you hear or see ?
It turns freely. I jumped the battery over to the starter side of the solenoid and it turned over. The previous owner said it worked, but the way some of the wiring was on the rest of the RV, I don’t think he knew what he was talking about. The start/stop switches detent sticks and I’m thinking it could be a switch issue. I ordered a factory switch for it yesterday. The fuel pump is not original and it stays on continuously when power is applied.
 

Henry J Fate

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Posts
1,916
If it cranks when jumped, a problem with the start circuit becomes first on the list. You will need to follow the start circuit until you get to the problem. As long as the control wires to the starting solenoid are correct, you could jump the bad switch out to see if it will crank. If jumping the switch out fails to crank the engine, either the wiring is incorrect or any other component in the start circuit could be causing the issue which will include a relay or two.

A service manual will show very clearly the start circuit.

Also, reading back in this thread, I found that the original poster did not have a cranking problem. It would crank but not start.
 

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