AdamG
Hello Everyone:
This is my first time posting a question so I apologize if I am doing something wrong. I am trying to fix a RPM SENSOR LOSS issue on a Generac CorePower 0058370 generator. During the weekly EXERCISE routine, the generator does not crank for the full 16 seconds and never performs a re-crank cycle. The RPM SENSOR LESS LED illuminates after failing the first crank cycle. I have installed a new battery and have measured the voltage at the battery and starter. It measures over 13VDC. I have also measured the gas pressure at the regulator and it's around 6 inches water column. I would appreciate any information or direction on trying to solving this issue.
Thanks!
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Peddler
Check the #18 wire to the coils, the controller is not seeing the engine turn over. We don't sell any core power units but I believe they get the RPM sense off the #18 wire going to the mag. Make sure it isn't disconnected or pinched or broken somewhere from the mag terminal back to the controller.
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AdamG
Thanks Peddler. I will check this wire tomorrow and post the results.
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AdamG
Hello Everyone:
I checked #18 wire today and I have good continuity from the in-line bullet connector to the controller. Also, since I disconnected the wires to the controller, I had to hold the "Set Exercise" button. The engine cranked over for only 4 seconds and then RPM SENSOR LOSS LED illuminated. It also never tried a re-crank cycle. Is there anything else to check/replace?
Thanks!
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Peddler
Check the #18 wire to ground with the meter set to measure AC volts. You should get a voltage reading, if so, what is that reading. It would be helpful if one of the contributors who have experience with these units would verify that the controller gets its run signal from the #18 wire. I know this is the case with other HSB air cooled units but know on this one.
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MacL
I'm surprised it doesn't actually start within the 4 seconds you say that it does crank. That it never tries to recrank is normal since it set a fault.
State your problem, not your diagnosis.
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AdamG
Hello Everyone:
With the generator running, I measured ~6VAC at the in-line bullet connector. With the generator off, I only measured mVAC with it slowly dropping down to ~.1 mVAC. Is there anything else to check/replace?
Thanks!

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Peddler
I think that is supposed to be about 7 volts but depending on your meter that could be ok. I would ohm the 18 wire while connected to the panel to ground it should be open with the switch in manual before it faults and then should indicate closed to ground when it faults. In the mean time I will try to find the correct voltage while cranking on the 18 wire.
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MacL
AdamG;53130 wrote:
Hello Everyone:
With the generator running, I measured ~6VAC[...]
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Wait. I thought it wouldn't start.
State your problem, not your diagnosis.
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AdamG
MacL:
If I keep toggling it between Off and Manual, it will eventually start. I believe it took 7 tries today. One other thing that I noticed today, while measuring the voltage of the #18 wire, is that while cranking the voltage is ~1.4 VAC when it doesn't start, but jumps to ~2.5 VAC when it starts. It then goes to ~6 VAC while running. I'm sorry for the confusion.

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BrianMartin
A bad magneto? Could explain why it takes so long to start (weak spark)... And if there is something wrong with the magneto, it could be sending a bad signal to controller via wire 18.. It's super easy to replace the magneto on this model, 20 minutes tops. The part isn't very expensive either.
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Peddler
I'm thinking a bad coil. When it starts does it run OK?
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AdamG
Peddler/All:
I was going to try and ohm out #18 wire today but it started right up. Also, once it starts up, it runs fine.
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AdamG
Hello Everyone:
Well, the generator started right up for the weekly exercise test. Based on the information from Peddler and BrianMartin, is this either a bad coil or magneto? If so, I am willing to replace both of them just to have some peace of mind. Can someone please provide the part numbers for these two parts and any other parts that may be worth replacing?
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BrianMartin
The ignition coil is what you want. Should be part #0H58410155, but I would double check that with Ziller before placing the order. Have you tried narrowing the gap of the spark plug a bit? If it turns over better with the smaller gap, I would say the coil is for sure your problem.
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AdamG
Hello Everyone:

I apologize for not posting a response sooner. I replaced the ignition coil (Ziller confirmed part#0H58410155), and the generator started within 4 revolutions. THANK YOU! I also used a feeler gauge to determine the spacing between the flywheel and the old magneto armature, and it was approximately 0.010". Is this correct? During the replacement, I also noticed a significant amount of rust on the flywheel and magneto armature. Is this normal? Should anything be done to minimize the rust? I also ended up installing a new spark plug (shipped directly form Generac), and it came pre-gapped at 0.040". The owners manual states 0.030". Does anyone know which one is correct?

I apologize for all the additional questions, but I am just a novice when working on this generator.
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BrianMartin
The rust is normal and isn't a problem, as long as the magnet is clean (you can use some emery cloth if it isn't). 0.010" is a good gap. I would narrow the gap on the plug.
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AdamG
THANKS BrianMartin & Peddler!
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