3B Altitude sensor

[gmac78]

Hi guys,

I asked this question a number of weeks back but never got an answer.

Recently when i was chasing boost issues i disconnected the F96 altitude sensor to take some readings. I drove the car to see what difference it made disconnected and made no difference what so ever. It was boosting the same connected or disconnected and did not raise a fault code.

Does anyone know if this is normal behaviour on a 3B?

Look forward to your replies.

Thanks
Gordon

[UrS4boy]

F96 Altitude/Barometric Pressure Sensor Information

There should be a 2223 blink code with the F96 disconnected with a corresponding reduction in boost pressure (the ECU assumes the elevation is 4000 m)(!!!) a sets the max boost pressure to the minimum (1 Bar??). Not sure why you are not seeing that. Are you running aftermarket chips in your 3B? That (safety) feature might be disabled in some aftermarket chips.

http://forums.quattroworld.com/s4s6/msgs/21892.phtml

[Tonks4x4]

My understanding of the altitude sensor is to alter boost in relation to ambient atmospheric pressure. However if its not plugged in i would imagine it defaults to sea level = 1 bar.
so having it plugged in will only make a miniscule difference as most of us in the uk are only a few hundred feet above sea level at most.

[gmac78]

I'm running the homefry from S2 central. Car running sound with no boost leaks but just not achieving 1.4 bar boost very often. I can sometimes achieve it in 4th or 5th gear if i load it up from low revs, not every time though. I can never get 1.4 bar in 3rd gear or lower. Does anyone know what a homefried should boost to in 1st,2nd & 3rd on a 3B? Just thought it strange that no fault codes were produced when running f96 disconnected?...

Tonks- you may well be right with that theory. Can anyone esle shed some light on the subject?
Cheers lads

[simon20vq]

I sold my homfried 3b ecu to orangepeel on here sometime ago, maybe you could drop him a line and see what he is getting.

[UrS4boy]

My understanding of the altitude sensor is to alter boost in relation to ambient atmospheric pressure. However if its not plugged in i would imagine it defaults to sea level = 1 bar. So having it plugged in will only make a miniscule difference as most of us in the uk are only a few hundred feet above sea level at most.

You are correct on the altering boost in relation to atmospheric pressure (higher elevation = lower atmospheric pressure = lower boost (to protect the turbo from over spinning in the thinner (less dense) air). However, the safety default (in the absense of a signal from the F96) isn't sea level (which would be potentially dangerous), it is 4000 m (very high = lowest boost).

[pasbogdan]

Nice info.Untill now the info about it was that it is used to get the boost higher at high elevations to keep power constant.

[newsh]

Have a search and you will find a thread about the testing procedure for this device. A few years a go we were all testing and adjusting them, then they don't get mentioned for years.. IIRC you can have a unit well out of spec without throwing a code.

[gmac78]

I've tested my sensor previously and was getting figures that were very similar to other lads on the forum. Off the top of my head i can't what they were right now, wrote them down somehwere but not at home at the moment to check. I fully expected a fault to be thrown when running disconnected, which makes me wonder if it's affecting achieving 1.4 bar boost? But again i was getting the same boost of 1.3 bar in 4th and 5th whether connected or not. Hmmm?

[johne]

Given that this sensor is of no use here in the UK, the easiest thing would be to replace it with a 5K ohm potentiometer adjusted so the centre point gives the same voltage as the ECU expects to see at sea level.

John