Just wanted to give everyone the heads up with what I experienced this weekend. Took the weekend off with my girl and went out of town to my families vacation house up in the local mountains at right above 6500 ft.

My car usually runs rich in boost but after 4000 ft the car began to go dangerously LEAN when I saw any boost. I luckily have a wideband and constantly watch it. In the higher altitudes the car would not give additional fuel and would stay between 14.5-16.0 if I tried to boost it, so I just kept it at a lower hear and kept her in vacuum with an AFR of 14.7. (luckily I never got it over 1.5 lbs of boost while going up) I did hear the car slightly detonate at 1.5 lbs of boost with lean AFR's but that was only for a second and my eye was actually on the gauges at the time. Good thing my girl was with me so I was taking it easy and the wideband was there to give me the news also.

On the way down it was the same till I got to about 3K foot level (Only time I got out of vacuum besides back up at around 6K foot level when I first left) and then things went back to normal.

 

Scary! Are you tuned?

I've never had this problem, but I am also tuned.

 

Untuned but it shouldnt matter IMO.

Higher altitude = less oxygen in the air = richer running conditions.
My comptech always ran PIG rich up there...
For some reason the ultimate didnt like the change in elevation.

 

stock MAP?

 

Yeah... I was going to say... at that altitude, it should be running richer than when at a lower elevation.

Andre

 

but at that higher elevation, since it is seeing less dense air, wouldn't it take away some fuel too?

i was told the stock MAP sensor doesn't do well with handling changes in air density (large temperature changes and altitude)

 

Yeah its a stock map sensor.

 

There is a barometric pressure sensor inside of the ecu. It made an adjustment that didn't agree with your tune. The leaning out is, as you said, to compensate for the lower air density, and maintain stoich. Your ecu doesn't know it has a compresser.

 

So just a problem with having a piggy back instead of a stand alone?

 

Shouldn't the EMU override whatever the ECU spits out?

Andre