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RV Repair/Onan generator won't start


1Partsguy wrote at 2007-04-21 05:32:30
I just recently had the same problem with my older Onan(6.5NHE-G 1990).  This could also be the voltage regulator.  The easiest test is to remove the electrical cover and disconnect the 12 pin connector leading to the voltage regulator.  Using a decent volt meter, check the continuity across the following pin combinations on the voltage regulator side of the connector): 5-9,7-9,9-10,9-12,AND 5-12 if any of these show open or direct short the regulator is bad.  Then check 5-10.  if this is an open circuit, regulator is also bad.  If all these test correct, the regulator still could be bad but this is doubtful.  after this check, reconnect everything and try to start the genset.  While cranking, check the voltage output from the genset.  If there is no output (A/C) then you either have bad brushes, voltage regulator (or worst case a circuit board).  To confirm the oil pressure sending unit is good, remove the 4 bolts on the cover around the oil filter and unplug the sending unit (then try to start the unit).  If it's gas you are worried about, unplug the fuel pump and jumper out the lead to the fuel pump on the main 12V input to the genset (the big red wire).  If you have 12 volts to the genset, you will hear the pump start (if not, it's bad).  Loosen the compression nut on the underside of the fuel filter (at the end of the discharge pipe from the fuel pump).  Use a back-up wrench.  With the compression fitting loose, you should gas a small amount of gas leaking out of the threads (make sure to tighten it when you are done, no need for any type of thread sealant).  If you are getting spark and gas, it will run unless the carburetor is out of whack.  The key here is the output voltage.  Without it, the circuit board does not sense that the unit is running and will not engage the run relay.  

JD wrote at 2009-02-18 15:47:35
In most cases it is a fuel problem with the described conditions especially if the generator set for more that a month without running.

Frank Nugent wrote at 2009-03-26 23:59:08
I ran into this very problem 2 years ago and before you do what I will tell you, check out the fundamentals such as fuel pump, ignition spark, cylinder compression, motor home fuel level, air cleaner, oil pressure sensor etc.

If all of these check good then the generator

voltage is low ( less than 90 volts). Now comes the work part. You have to remove the generator from the Motor Home and clean the commutator and free up the generator brushes in their holder. Sometimes the brushes are jammed with sand or dirt and do not contact the commutator rings properly.Once you have done this, the motor will start and run normally.

Good luck


glen wrote at 2009-11-08 19:51:13
i also have this same problem, and the shop told me that i have a cracked fuel line at he tank, but i dont smell any fuel and im getting fuel to the carb, i think they are wrong and just want $700 bucks to fix

JIm wrote at 2010-05-16 20:54:05
Where is teh fuel pump? If teh fuel line is off the  carborator and I turn it over should gas pump out of the line?

COuld it be a fuel filter?

It was ideling poor now it will not start

Fishfrye wrote at 2010-09-18 22:46:13
My will run when it wants to! I think it is heat related (outside temp), it shut down when it get hotter. I had fuel at the carb. last night, adt it shut down at noon and I could not get gas when I hit the primer. As soon as I got home it starter right up. My thoughts are that the fuel pump is locking up when it gets hot. Anyone have any experience with this?

ben wrote at 2014-07-12 17:13:40
your carburetor is not getting enough fuel...make sure you have more than 1/2 tank of gas in the rv, when you do try to restart, if it still cuts out after 10 seconds, you have to replace your fuel filter...that should do the trick...ben

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Bill Kaltenekker


I own and operate a large RV repair and service center in Alaska. I am also an electrical engineer. I can answer RV maintenance and repair questions from the front bumper to the back. Engines, transmissions, differentials, suspensions, appliences, hvac problems, electrical problems or whatever you are having trouble with.


I am an electrical engineer, physicist. I own and operate a large RV repair and service center in Alaska. This is my 6th season.

MS and BS in physics from the University of California in Santa Barbara.

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