Post by lowtechguy on Mar 2, 2007 10:11:22 GMT
When operating hot in closed loop the ecu reads the oxygen sensor and decides if the exhaust is correct.
If the fuelling is lean it will adjust the fuelling incrementally eg: by 10% at a time until it's right using the 'short term trim' function, and then reprogramme the fuel map/memory with a new setting called the 'long term trim' which will go up to 10% - the value tested & proved correct with short term trim, when that's done it will reset the % adjustment on the short term trim for that load position to zero.
It takes a few seconds for the long term to stabilise and thus I would expect, on a hot engine with fully functional Lambda at steady idle that the short term maybe might show small % for a period and then drop to zero, with a commensurate increase in the long term value at that speed.
Any faulty part in the fuel or ignition system be it plug, lead, injector, sensor can upset the fuelling and the trim systems will try to compensate. However if the short term value is at a very high limit (ie: at max all the time) the ecu cannot cope with reprogramming at all, because it depends on some response available from the short term to test alterations.
www.guy-croft.com/viewtopic.php?t=783
If the fuelling is lean it will adjust the fuelling incrementally eg: by 10% at a time until it's right using the 'short term trim' function, and then reprogramme the fuel map/memory with a new setting called the 'long term trim' which will go up to 10% - the value tested & proved correct with short term trim, when that's done it will reset the % adjustment on the short term trim for that load position to zero.
It takes a few seconds for the long term to stabilise and thus I would expect, on a hot engine with fully functional Lambda at steady idle that the short term maybe might show small % for a period and then drop to zero, with a commensurate increase in the long term value at that speed.
Any faulty part in the fuel or ignition system be it plug, lead, injector, sensor can upset the fuelling and the trim systems will try to compensate. However if the short term value is at a very high limit (ie: at max all the time) the ecu cannot cope with reprogramming at all, because it depends on some response available from the short term to test alterations.
www.guy-croft.com/viewtopic.php?t=783