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Ask Hank F. Your Own Question
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14675
Experience:  Certified on Onan and Generac generators
19372534
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Onan 6.5 45 volts to fuel pump

Customer Question

Onan 6.5 45 volts to fuel pump
Submitted: 1 year ago.
Category: Small Engine
Expert:  Hank F. replied 1 year ago.
Hello!
Thank you for requesting me.
Is the genst running smooth when it runs, or is it showing signs of running rich?
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Customer: replied 1 year ago.
It's running smooth. But it keeps burning up the fuel pump. Is it supposed to have that much voltage supplied to the fuel pump when running?
Expert:  Hank F. replied 1 year ago.
Absolutely not - the high voltage will burn the pump up.
That voltage is also what is powering the coil - it is a wonder you are not burning up the coil, too.
The most likely culprit here is the bridge rectifier.
Inside your control box, mounted all the way on the back wall, is a small square about 1- ¼” across, with 4 terminals on it. Your unit is old enough that if it still has the original BR, it will be round instead of square. 2 of the terminals are marked AC, one is marked +, and the other is not marked at all. This is the bridge rectifier.
Remove the rectifier. Pay strict attention to which wires go to which terminal and remove all wires from the rectifier. Mark one of the AC terminals with a marker or piece of tape. Call this AC1, and the other AC2.
Set your meter to ohms and perform the following 4 tests:
1. Red lead to AC1, black lead to +. Record the reading.
2. Black lead to AC1, red lead to +. Record the reading.
3. Red lead to AC2, black lead to +. Record the reading.
4. Black lead to AC2, red lead to +. Record the reading.
What are the results of these 4 tests?
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Customer: replied 1 year ago.
I gained access to the rectifier but there are no markings on it.
Customer: replied 1 year ago.
Ok so I found a positive and negative on it but that's it. No other markings
Customer: replied 1 year ago.
If I did this right, these are the readings I came up with
1. .810 ohms
2. 11.60 ohms
3. .738 ohms
4. 9.75 ohms
Expert:  Hank F. replied 1 year ago.
The positive and negative will be across from each other, with the 2 AC tabs in between.
The readings you got, was that flat ohms, or was it M-ohms?
If it was flat ohms, your BR is bad.
With red lead on + and black lead on AC, you should have gotten a minimum of 1 M-ohm.
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Customer: replied 1 year ago.
It was m ohms
Expert:  Hank F. replied 1 year ago.
On which readings?
You need to be specific - I can't see or hear what is going on, and only know as much as you tell me.
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Customer: replied 1 year ago.
On all of them it had an m next to the ohms
Expert:  Hank F. replied 1 year ago.
If they all had M-ohm readings, then the diodes in the BR are open, and the BR is bad.
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Customer: replied 1 year ago.
Ok. I'll order one andlet you know. Thank you.
Expert:  Hank F. replied 1 year ago.
OK
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Customer: replied 1 year ago.
I keep getting an email to rate you. Should I rate now or wait till the part comes in to see if it fixes my problem?
Expert:  Hank F. replied 1 year ago.
That is up to you - you can rate now or later.
Those emails are automatically generated by the system, and are sent on a specific time schedule. You can ignore them.
If you prefer to rate now to stop getting the emails, rest assured that you will still be able to access this question.
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Customer: replied 1 year ago.
I installed the new bridge rectifier and still have the same high voltage problem. What next?
Expert:  Hank F. replied 1 year ago.
How much voltage is the genset putting out now?
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Customer: replied 1 year ago.
The voltage to the fuel pump. Should I be measuring in DC or ac? Cause ac I'm getting 45 volts to the fuel pump and DC getting 70 volts
Expert:  Hank F. replied 1 year ago.
No, I'm askign about the 120 side of things.
Is it still at 128VAC, or has it changed?
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Voltage to the fuel pump should be DC.
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Customer: replied 1 year ago.
128-129
Expert:  Hank F. replied 1 year ago.
This is really weird.
On the back side of the generator housing, there is a long round resistor.
Disconnect one of the wires from the resistor, and ohm across the resistor. What does it read?
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Customer: replied 1 year ago.
Ok. Where is it lacated If I'm looking at the generator? I'll have to do it tomorrow. Out of light.
Expert:  Hank F. replied 1 year ago.
As I stated, it is on the back side of the generator housing, above the starter.
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