Just a passing thought that didn't pass quick enough.... Can anyone tell me...
Why is the atmospheric pressure important to my ECU when it has no control of air intake or fuel?
Purpose of barometer
Moderator: RichardW
What car is it on, derv or petrol & is it forced induction or n/a? I assume you mean maf or map?
The sensor will talk to the ecu to tell it airflow & i imagine it will adjust the fuelling/ign/timing etc according to load etc.
The sensor will talk to the ecu to tell it airflow & i imagine it will adjust the fuelling/ign/timing etc according to load etc.
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98 Xantia Hdi Lx with a/c (105k)
97 Renault Extra (c1j turbo 230+hp, 12.88@106)
91 Renault 5 Gt turbo (68k minter)
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Yes, timing related Mike as that's all the ECU controls.
Fact is, at high altitudes where the air is thin the ignition delay (i.e the time between the fuel being injected and starting to burn) is longer because of the less oxygen available.
Therefore if the ECU knows barometric pressure it can advance the timing to compensate. It might do little for power but will help emissions.
Fact is, at high altitudes where the air is thin the ignition delay (i.e the time between the fuel being injected and starting to burn) is longer because of the less oxygen available.
Therefore if the ECU knows barometric pressure it can advance the timing to compensate. It might do little for power but will help emissions.
Jim
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But surely, as it's a TD then the turbo will be able to compensate for lack of oxygen.
I read years ago that turbos compenated for the loss of air pressure, and therefore power, as you climbed higher and higher. I'm thinking partucularly of the Audi Quattros climbing Pike's Peak in the 80s.
I read years ago that turbos compenated for the loss of air pressure, and therefore power, as you climbed higher and higher. I'm thinking partucularly of the Audi Quattros climbing Pike's Peak in the 80s.
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Hi Jim, that was all I could think of but I didn't realise timing is a smoke factor except at higher revs.
Bit of trivia; The mechanical equivalent is the Bosch pump ADA - which is simialr in appearance and function to the LDA (ufo) but works the other way - to reduce fuelling relevant to air pressure.
Taking it to an extreme, can advancing/retarding the timing go some way to curing off-boost smoke?
Bit of trivia; The mechanical equivalent is the Bosch pump ADA - which is simialr in appearance and function to the LDA (ufo) but works the other way - to reduce fuelling relevant to air pressure.
Taking it to an extreme, can advancing/retarding the timing go some way to curing off-boost smoke?
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Thanks to Toby for showing me the way, I managed to find some Citroen literature on the subject. They call it an "Altimeter Corrector". It is also used to calculate EGR control which is interesting as this obviously affects AFR as well (presuming the EGR is working).
It would be interesting to experiment with different corrector inputs to see how much and when the timing changes in relation though being at sea level, I guess my ECU's already operating in the more advanced area of the map.
Interesting stuff and thanks to all that responded.
It would be interesting to experiment with different corrector inputs to see how much and when the timing changes in relation though being at sea level, I guess my ECU's already operating in the more advanced area of the map.
Interesting stuff and thanks to all that responded.