Hello all: I recently noticed something that had escaped my attention previously: the ICE on my 2009 doesn't always sound the same. For example: let's say that I start the car, but don't drive anywhere. At first it's just in EV mode. After some time the ICE will start to bring itself up to temperature, charge the traction battery, whatever. Eventually the ICE will turn off again. But sometimes, prior to turning off, the ICE will get much "quieter". In other words it goes from having a "rough" four cylinder sound, to a very "smooth" sound, like it is a small 6 or 8 cylinder. Then after runing for several seconds in this mode, the ICE will shut off. Anyone know why this happens? Is the timing changing? Some emission control valve opening or closing? Just wondering.
The ICE changes valve and ignition timing as needed. During the warmup cycle, ignition timing is retarded to allow more unburned fuel to the catalytic converter. In this case the engine is very lightly loaded. Other times the engine may be working hard to recharge the battery. There are a lot of permutations. Tom
