Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.Initially, does the fuel contaminating the oil happens only when the Mule is used? ...or even when just parked?
Do you have access to a volt /multi-meter?
An injector would have two (2) wires to it. 1 of these wires would have a constant voltage and the other would be pulsating when the engine is running.
Unfortunately, it would appear that way; a faulty injector.
Also, the 13.9V would seem a bit high.
Are you considering / attempting a check/clean of the injectors?
Good luck and thank you for the opportunity to share the information.