I am tuning a 7747 and was curious if altitude effects BLMs. If you fine tune at sea level what if any will be the change at 7000 ft msl. Any one have thoughts on this?

 

MAP cars (SD and TBI) are automatically corrected for elevation by the MAP sensor. As you go up in elevation, the Kpas for a given load goes down. As long as you have GOOD VE table values, then the ECM will be able to correct properly (for mixture).

 

I follow that for normal driving/non PE mode. What about PE mode and WOT? If correct at sea level will A/F for WOT be correct at increased altitudes?

 

I think you're forgetting that the MAP sensor is adjusted during altitude changes AND engine needs. The BLM will still be around 128 but you might be in the 50kpa instead of the 40kpa range. It's kind of cool how it all works together.

 

Yes It is pretty cool.

I saw a discussion on another forum "The car has a high altitude chip if you go to sea level you will need a different chip". I thought I might be missing something but you confirmed what I was thinking.

Thanks

 

The pcm will compensate for the change in altitude or barometric pressure on the day BUT that is the whole point of the pcm being able to have self correction offset ie BLM to compensate for the arrors that can arise due to things like altitude error / air density issues etc.

IMHO do all your tuning at the conditions the car spends most of its time in and the BLM table in conjunctune with the other compensation table will self compensate for any abnornal external influences.

Just because the engine is "perfectly mapped" during summer does not mean that it will be perfect during other season BUT that is where the benifits of sticking with out OEM engine mangement shines over everyhting else.