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05 s60r gt

Right now in kansas I make 10psi threw all gears and yes this is the detune version and plan to get a new tune. Over the weekend my car would boost around 16psi and spike around 19. Up in the high Rockies. Can anyone tell me why I was getting those psi reading when it tune at 10psi. No boost leaks everything working right. I do know higher altitude the more denies.

I would think at any temp or altitude it would be the same boost since it computer controlled
 

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ECU sets absolute boost pressure, boost gauge reads gauge pressure which differs by the atmospheric pressure. For example, up past a mile the atmosheric pressure is about 2 psi lower which will make the gauge read about 2 psi higher since the ECU is trying to set the same manifold pressure it did at sea level. It would not explain over 5 psi difference, so I'd more assume some of your sensors and/or actuators are getting old and not adapting to the change of pressure as well as they should.

For example, at sea level I make 18-20 psi of boost, but at over a mile that jumps to 20-22 psi.
 

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You will also notice this during warmer and colder temps. Your car will have to boost more in the summer due to less dense air than in the winter.
 

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The Bosch Ecu adjusts boost to compensate for altitude even from the factory, which is why these cars feel so fast for only 300 hp at altitude. The ECU will compensate all the way up to about 6,500 ft above sea level.

Because the factory ECU is looking for a torque/hp target and not just a specific boost amount, it can raise and lower boost and timing to make the hp it wants.
 
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