I have a discussion with a friend of mine about what happens at higher altitudes. I said that when you are at a high altititude, because the air is thinner (less condense air) that the ECU will automatically account for this by pumping less fuel (run lean). He thinks that the ECU will pump more fuel (run rich). Can anyone tell me which of these is correct?


Thanks!!

 

cold air is more condensed so there will be more volume of oxygen with colder temp air than hotter air. I would think the ecu would add more fuel but either way the ecu basically tunes the engine itself in closed loop.

 

The air at higher atltitudes is less dense, therefore having less oxygen per unit. I wanted to know how this affects the engine and fuel.

Thanks!

 

Runs leaner, but has other side effects as well. A common chop mod for DSMs is to fool the ECU into thinking you're at some outrageous altitude. It disables the random misfire sensor, mostly ignores the knock sensor, and a couple other goodies.

 

The O2 sensor will tell the ecu that less fuel is needed, and so less will be pumped.

 

Well, at a higher elevation there is less oxygen in the air. Theoretically, wouldn't if you have less oxygen, and ran the same fuel maps, wouldn't the car run richer? Comparing my altitude 3100ft and Phoenix altitude, 1100ft. my car ran a bit leaner in Phoenix, no change in the VAFC. But, I'm not sure if this is true with a "stock" ecu or not. The MAP sensor would account for the change in pressure I believe, but I don't know if it would make that much change to the fuel map. I'd like to see what everyone else says too.

 

the car would initially run rucher but then the ecu will "lean it out" to make the correct mixture (neither lean or rich)

 

Thanks guys!!