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Hank F.
Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 15198
Experience:  RV tech since the beginning of the millenium.
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onan Quiet Diesel 7.5 kw in a motor home ...reassembled

Resolved Question:

I have an Onan Quiet Diesel 7.5 kw in a motorhome. The rotor magnets came off destroying the rotor and stator. I purchased and replaced the rotor and stator and reassembled. I primed the fuel system and then tried to start the genny. It would crank for about 15 seconds, with a little black smoke from the exhaust. Then it would stop cranking. Fault code 27.

I have disassembled the unit again. I found nothing wrong..all wiring seems correct and reassembled. Same thing. If I disconnect the stator leads, the engine will start and keep running as long as I hold the start button down. When I release the start button, I get a fault code 26.
Submitted: 5 years ago.
Category: RV
Expert:  Hank F. replied 5 years ago.
Thank you for choosing Just Answer for the solution to your problem.
My name is XXXXX XXXXX I am going to assist you with this.

What is the full model number of the genset?
Customer: replied 5 years ago.
Spec H
Expert:  Hank F. replied 5 years ago.
Code 26 and 27 are completely different codes. We need to figure out which one is active.

To do this, we will need to reset the controller.
Do this by removing the positive battery cable from the genset for 10 minutes, then reconnecting.
Now try and start the set, and see which code comes up.
Customer: replied 5 years ago.
OK, will do, but...
As I said before. If everything is hooked up, the engine cranks for about 15 seconds, then stops cranking and gives a code 27 - unable to sense PMA frequency.

The code 26 occurs when I try to start it with the stator leads disconnected. In that case the engine runs as long as I hold the start button, but stops immediately when I release it. The engine is actually running at something near a normal rpm.
Expert:  Hank F. replied 5 years ago.
The code 27 is only due to 1 of 3 things:

1. The stator leads are not properly connected.
2. The stator is bad, and not putting out any power.
3. The inverter is bad.

But let's make sure the code is correct.
Customer: replied 5 years ago.

1. Stator is new. Leads are connected as per labels printed on the wires.

2. I don't have a precision ohmmeter, but I have checked all the lead to lead resistances with a digital multimeter and they all read 2 ohms.

After 15 minutes with battery disconnected, the code is 27.
Expert:  Hank F. replied 5 years ago.
If you are absolutely certain the stator is securely connected, then the inverter is going to be bad, and will need to be replaced.
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