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Ask Hank F. Your Own Question
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14489
Experience:  Certified on Onan and Generac generators
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I have trouble with a Guardian 20Kw Model 58750 with Nexus

Customer Question

I have trouble with a Guardian 20Kw Model 58750 with Nexus Controller 0H6680A.
Recently I did a periodic maintenance(replace air filter, spark plugs oil and oil filter).
After this the generator Start Hard and Runs Rough.
What could go wrong in the maintenance?
Submitted: 1 year ago.
Category: Small Engine
Customer: replied 1 year ago.
I have error message on the screen saying "Low Voltage"
Customer: replied 1 year ago.
Check video to see what the trouble is.
http://youtu.be/NZ4Du_Zqh8E
Customer: replied 1 year ago.
My bad,
The error message is "UNDER VOLTAGE"
Expert:  Hank F. replied 1 year ago.
Hello!
My name is ***** ***** I am going to assist you with this.
What is the serial number of the genset?
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Customer: replied 1 year ago.
S/N(###) ###-####Guardian 20kW Running on NG.
Customer: replied 1 year ago.
I have trouble with a Guardian 20Kw Model 58750 with Nexus Controller 0H6680A, running on NG. Generator was installed in 2010. Recently I did a periodic maintenance as I do twice a year(replace air filter, spark plugs oil and oil filter). After this the generator Start Hard and Runs Rough. Once it start the Stepper Motor moves, increasing and decreasing RPM for almost 1 and a half minutes. Some times reach normal speed, some times doesn't, then halt and show an error message "UNDER VOLTAGE". I Run all test on problem 17. - Check Fuel Supply - Ok. - Running on NG - Ok. - Replace Air Filter - Ok. - Check Choke Solenoid -Ok. - Check for Ignition Spark -Ok. - Check Spark Plugs - New - Ok. - Check Valves- Ok. - Check Stepper Motor Control - Ok. - Check engine Compression - Ok. - Check Flywheel Key - Ok. The last thing "CONTACT TECHNICAL SUPPORT" - "NO SUPPORT FOR HOME OWNERS" What could go wrong in the maintenance? I always use genuine parts. This is not the first time I do the maintenance on my unit.
Expert:  Hank F. replied 1 year ago.
What you are seeing is called surging.
Surging is usually caused by not enough fuel getting to the engine.
There is a diaphragm inside the demand regulator, and sometimes the diaphragm gets dirty or stiff, and won't allow enough fuel to flow.
On a stiff diaphragm, this can cause hard starting and/or rough running until the diaphragm loosens up,.
What you need to do is to have the fuel system on the genset tested for proper flow.
Unless you have had gaseous fuel training, and have the proper equipment, this is not something you can do yourself.
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