Aussie Colorado RG 2.8lt lacking power over 500m altitude

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. 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.

Attachment 128556 torque limit by altitude

Attachment 128557 desired boost medium altitude

Thanks in advance :)

It may be a torque reduction event at altitude which will limit the amount of fuel delivered. The target boost map references fuel delivery in mm3 on one of it's axis so that will therefore limit the amount of boost generated.

Hi JasonHSV and all

Thanks a lot for the reply mate. I've been doing my own investigation's downloading demos of EFI Live and HPT and stock files off the forums to try and understand a bit more about tuning, as car still runs perfect at sea level, so really does seem related to altitude my lack of power.

When you are tuning a turbo engine, do you normally adjust the 'Desired Boost by med altitude' table as well?

Seems like others based on some tune files I've seen on here for a Colorado, but in my car which was tuned in WA, the tuner has left the med/high altitude files as stock to prevent turbo overspeed etc in his words. Looking at the difference in desired boost on the stock file between low/med altitude, appears GM targets similar boost levels just higher in the rpm range on the med altitude mapping


Attachment 129266

Attachment 129267

Thanks in advance :)

Can you post the whole map file here? It's hard to figure out stuff by screenshots.
What is the exact model of the turbocharger on this engine? And if you have the logs, it would be nice to have measured mass airflow at sea level and at altitude.

But anyhow, a turbocharger works by multiplying pressure. If you boost 300 kPa MAP at sea level, this means the turbocharger is operating at the pressure ratio of 3. Up high in altitude where you see only 93 kPa of ambient pressure, with that same pressure ratio of 3 you should see 279 kPa MAP, not 240 kPa. You are missing 0.4 bar of boost.
In both of these scenarios, the compressor speed is almost the same. In fact, at the same pressure ratio with lower ambient pressure, the speed of the compressor should be lower because you are effectively moving less mass of air therefore moving the operating point to the left on the compressor map towards the surge line.

And i doubt that you're operating even close to the limit of the turbocharger, you should get much bigger boost in lower RPM ranges where the mass flow of air isn't that big (to get the same MAP like at sea level). Looking at the compressor map for this turbo will help.

Quote:

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Originally Posted by sbarisic

Can you post the whole map file here? It's hard to figure out stuff by screenshots.
What is the exact model of the turbocharger on this engine? And if you have the logs, it would be nice to have measured mass airflow at sea level and at altitude.

But anyhow, a turbocharger works by multiplying pressure. If you boost 300 kPa MAP at sea level, this means the turbocharger is operating at the pressure ratio of 3. Up high in altitude where you see only 93 kPa of ambient pressure, with that same pressure ratio of 3 you should see 279 kPa MAP, not 240 kPa. You are missing 0.4 bar of boost.
In both of these scenarios, the compressor speed is almost the same. In fact, at the same pressure ratio with lower ambient pressure, the speed of the compressor should be lower because you are effectively moving less mass of air therefore moving the operating point to the left on the compressor map towards the surge line.

And i doubt that you're operating even close to the limit of the turbocharger, you should get much bigger boost in lower RPM ranges where the mass flow of air isn't that big (to get the same MAP like at sea level). Looking at the compressor map for this turbo will help.

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Hi Sbarisic,

Thanks for the reply, I don't have the HPT hardware to get my actual mapping, just the demo and some stock files I found here on the forum to try and understand things a bit more myself - see attached.

I think the turbo is a Garrett GTV1752VKL from what I saw online, I've emailed Garrett for a compressor map but at the moment only have the estimated speed map from the HPtuners file which I guess the ECU uses to prevent turbo overspeed. I assume this should match the Garrett compressor map but not sure.

Attachment 129285

Re your point "with that same pressure ratio of 3 you should see 279 kPa MAP, not 240 kPa You are missing 0.4 bar of boost." - yes assuming the turbo is still in the safe operating range, I think since the tuning has not adjusted the medium altitude map, the stock desired boost is max around 240kPa

I think potentially they also don't adjust this Max Boost by barometric pressure by rpm map as below much, e.g. maybe only for sea level at 100-102kPa so the higher altitude / lower barometric pressure situations, the stock limits still are being applied which results in a big drop off under 96kPa (~500m) which is where I am seeing my issue start

Attachment 129286

Thanks in advance
James

All the low med and high altitude maps should have been increased by the same amount. And honestly, looking at the stock "13220 Desired Boost Max vs. Baro vs. RPM" table, it doesn't look good. 2200 RPM at 96 kPa baro it's 284 kPa boost limit, while 93 kPa baro it's 249 kPa boost limit.

Thanks Sbarisic

Yeh I think my car is likely hitting the limits of that table "13220 Desired Boost Max vs. Baro vs. RPM" and changing it from tuned up to 300kPa back to stock pretty quickly over 500m altitude which doesn't seem high, but maybe that is required to protect the turbo.

Garrett sent me a link to the compressor map - https://www.garrettmotion.com/racing...owermax-turbo/

Some quick calcs going through this to calculate pressure ratio, https://www.garrettmotion.com/wp-con...3_Expert-1.pdf

MAP - 300kPa (tuned) +14kpa (estimated loss due to intercooler/piping etc - Garrett estimate of 2psi) / 101kPa atmosphere - 7 kpa (estimated from air filter - Garrett) = 314/94 = 3.3 pressure ratio

At stock MAP 258kPa this is 2.9 pressure ratio

Up at 500m, 95kPa barometric reading, then

MAP - 300+14 / 95-7 = 314/88 = 3.57 or stock - 258+14 / 88 = 3.1

I think the max pressure ratio in the stock file is 3.65 which matches the compressor map, so it is very close to that limit running 300kPa at 500m altitude.

Probably doesn't need to drop right back to stock though if the pressure ratio is 3.1 - probably a MAP around 280kPa would be ok at 500m altitude still I guess provided it is derated further as altitude increases.

Thoughts?