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318/P218G starting issue diagnosis

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#1 rallyroo OFFLINE  

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Posted September 29, 2016 - 07:21 AM

My '88 JD 318 with the Onan P218G is having an issue starting. When the key is turned to the "start" position, the solenoid clicks but doesn't engage the starter motor. This seems like a relatively common issue, and the previous owner had installed the relay kit to supply the solenoid with better voltage. It will occasionally turn over after maybe 15-20 cycles of the key, but seems like it's getting less and less frequent. 


Here's what I've checked so far: key switch and starter circuit connectivity is good; the circuit trips the relay no problem when the key is moved to "start". The relay is installed correctly, and all pins are clean and connected properly. 


Battery voltage was a tad low, ~11.5V. I tried hooking up my car's battery which boosted voltage to ~13+ but this made no difference.


I can get the starter to spin but not engage by shorting the two studs on the solenoid with a screwdriver. I can get the engine to crank and start by shorting the two studs while holding the key in the start position. This indicates to me (and my very limited knowledge of such things!) that the solenoid itself is the culprit. Could the plunger be functional in that it moves the starter gear back and forth, but not making solid connection between the studs? 


When I bought the tractor, the PO mentioned that he had replaced the solenoid when he installed the relay kit to try to fix the issue; is there any indication that this had been done? Should I just go ahead and replace the solenoid, or are there any other diagnostics I should try beforehand? Also, do I really have to pull the entire engine to replace the solenoid, or is there a better way to get in there?


Thanks for the help!

#2 chieffan ONLINE  

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Posted September 29, 2016 - 08:20 AM

If the engine will crank and start by shorting out the solenoid you have probably found the problem.  Not familiar with you model of Onan but on my BF MS the solenoid is under the battery tray.  Have to lift the motor to get the starter off and on.  Could be your starter needs some attention also, like bearings lubed and a shot of graphite on the drive.

  • rallyroo said thank you