Hi all
Had my car tuned about 10 months ago, I live in a very flat part of the country and now over on the East Coast of Australia which has a lot more hills and mountain ranges.

When travelling from sea level up to over 500m altitude I am noticing a significant lack in power and turbo spool up, boost etc. Normally max boost of the tune at sea level is 300kPa MAP, when the issue is occurring only achieve 240kPa max.

First occurred when towing our caravan out slight hills at 500m and we where 2nd gear 2750rpm and not accelerating just holding speed, boost than was maxing out like 150kpa MAP. A passer by helped tow our van to the next town and as we came back to sea level, car was back to full boost. Has happened numerous times now and is clearly related to altitude.

I've done the following to the car to rule out anything else mechanical - cleaned MAF, MAP sensors, new air filter, mechanic did a smoke test to 13psi - intercooler and all hoses fine, turbo vane actuator test -passed, full sensor relearn, and disconnect battery for 30 mins to reset ECM and also up at altitude. I also tried a new MAP sensor but didn't fix it either, and my barometric reading from the ECU seems correct and adjusts up/down altitude correctly. Barring a very strange turbo issue which only somehow occurs at 500m up, it really feels like once the altitude increases and the barometric pressure drops to around 95kPa (from normal 101kPa) at sea level with the higher altitude, the lack of power issue occurs. Seems to me from driving the car this is somehow being commanded by the tune, at a lower altitude than any drop in power should occur.

I am currently on the otherwise of the country - 4000km away, so can't really go back to the tuner, plus would be impossible to recreate the issue there as my home state is very flat overall.

The tuner has sent me a few images of the tune settings but overall very cagey about it all and says nothing he touched would do this.

Apparently there are 3 altitude settings in the Colorado ECM - low/med/high, does anybody know how the ECM determines which altitude level it is at? If it is based of barometric air pressure, does anybody know what level it changes from the low to medium altitude map?

There is also apparently torque limiting/reduction by altitude. The tuner didn't send me a very high resolution image of that but I can see in that table the first setting is 93kPA down from 100kPa, than 90kPa, but the reduction appears to be very minor until 80 or 85kPa - corresponding to ~1500 to 2000m altitude which is basically higher than any road you can drive in Australia!

Thanks for reading if you made it this far! Any insight into the mechanics of how the ECM determines when to adjust for altitude, when to change the desired boost map from low to medium altitude etc.and to understand how it could potentially be occurring earlier than it should, as to me the car should drive exactly the same at 500m altitude as sea level, and pretty much the same at 1000m.

I'm also wondering how the desired boost by altitude tables interact with the torque reduction by altitude, do these interact and multiply, or a stand alone and the torque reduction by altitude just sets a limit that is the set desired boost at that altitude was going to go over it would start to reduce feeling to limit.

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ID:	24347 torque reduction by altitude

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ID:	24348 desired boost medium altitude

Thanks in advance