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Barometric corrections on a VE-based ECU

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Hi,

Wondering if you think barometric corrections should be needed on an ECU that uses VE as a fuel model. In my opinion, that shouldn't be needed, since the air pressure is already factored in.

Thanks!

This is an age old debate and the answer is really going to depend on what kind of changes in barometric pressure you actually see. If you're only seeing relatively small changes (pretty consistent altitude and only day to day baro fluctuations) then i personally wouldn't worry and an ECU that uses MAP as the load input (VE or traditional) will cope just fine. If on the other hand you're expecting large variations in baro (maybe you live in mountainous terrain) then relying solely on MAP can start to see some error creep in to your fuelling/ignition. While MAP adequately accounts for the changing pressure in the inlet manifold which in turn is affected by barometric pressure, what it fails to account for is the effect of barometric pressure on the exhaust. After all, the airflow through the engine is an aspect of both inlet manifold pressure AND exhaust manifold pressure.

The general consensus is that the most complete way to model baro changes and their affect on the engine is using an EMAP sensor and an ECU that provides IMAP/EMAP as a load option. Alternatively most ECUs these days will allow the option of a baro sensor which can then be used as a axis for a compensation table.

Thanks for the reply! I wasn't considering the effects of atmospheric pressure on the exhaust and, by extension, on engine VE. Makes total sense. :)