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Quad is 2008 Sportsman 500 EFI....What happens with the quad is when I first start it up it idles and runs fine after quad warms up I notice a engine misfire at a specific RPM range of 4600 - 5100 below and above this range the quad runs fine. I'm wondering if the TPS has a issue where when it warms there is some kind of defect that is expanding and sending an errant signal to the computer messing up the timing and fuel delivery. When TPS contact is above or below this problematic area on the TPS quad runs fine. I've replaced the plug and plug wire. Anyone have any thoughts on why quad is acting up at this specific RPM range. Thanks for any insight on this.
 

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Update....could not find any issues with the TPS so took machine into dealer. Digital wrench did not find any codes and dealer was also stumped. They say it most likely is the clutches and upon talking with a couple of other people and describing the problem we are leaning towards the secondary. Symptoms are non existent when revving the the machine in neutral to approx. 5200rpm...ie. no apparent missing or stumbling...we even jacked up back end put machine in High gear and revved to 5200rpm...with no load it didnt seem to stumble. Primary is super clean and all wear items are in spec (buttons, no play in shaft, weight pins replaced, new springs in both primary and secondary (QSC kit). Secondary appears in very good condition as well so I am still not completely convinced clutches are issue but who knows.
 

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Wiring connections can cause a problem like you describe - sometime just unplugging and plugging things will solve the problem and since it occurs at a specific RPM range it is most likely vibration sensitive. Be sure to check ground connections - just because they are tight does not mean it is a good connection - like the wiring connectors, loosen and tighten all the ground connections.
 

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Yeah I'd look into wiring issues. Pull the plastics and go over the wiring. Look for damaged wires. Chk all the connections. Even the battery connections.
 
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