Old school tuners are sometimes thrown a curve ball when a sled with a newer ignition system is causing the performance to be reduced. Often it goes like this; a tuner is having difficulty reaching their desired peak operating RPM, and concentrates on the clutching and gearing variables. They will often notice the machine runs real strong when cold, but performance drops off noticeably when it gets heat soaked.
While you may always notice a slight difference between cold and hot performance, many times it is by design the ignition system and on-board electronics are making a programmed decision. Water temperature is an input used by all modern sled ignition and fuel delivery systems, and as this temperature rises past predetermined temperatures, things like ignition timing and fuel delivery are adjusted to compensate for the engine temp. Bottom line, when this happens you will on occasion notice it. Discriminating tuners will notice it most, and if theyâ€™re not aware of how the exact system on their sled works (is programmed) they may waste time worrying about problems that donâ€™t really exist.
Common is a Polaris RMK with mods that runs flat on a particular day. It doesnâ€™t want to pull full RPM, and just isnâ€™t as good as it should be. You have to be able to discern if the water temp is actually high, or if there is a detection (sensor) problem. Most often it is an actual high coolant condition, caused by a host of variables, normally inadequate cooling by the extrusion system for the given snow conditions. Different types of snow/ice provide different heat exchange rates, and heavy pulling conditions as often seen in mountain riding can bring the water temp to one of the many levels of compensation that todayâ€™s â€œsmartâ€ machines have.
Each make and model employs a different set of instructions the on-board computer is analyzing to make its adjustments; with the newer injection systems, the complexity of the systems increases. While it provides improved engine reliability and performance consistency, it is nice to know what is actually happening when it isnâ€™t running as good as it could be.
Another classic is on a sled with an airbox temp sensor that is supposed to measure the temperature of the air flowing through the airbox. You run the sled hard for a while, then stop and park for a few minutes. The heat of the engine compartment heat soaks the airbox and temp sensor. You go to take off and the sled acts very lean when trying to start it. Why? The sensor told the computer the air was very warm, so less fuel was delivered at start up. As soon as some air started to flow past the sensor, this condition was corrected and away we go.