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Just the facts please ...
1,030 Posts
Discussion Starter #1 (Edited)
Do long term fuel trims show how far the ECU needed to adjust fuel to get to it a specific setting; and does the short term trims show near term adjustments to reach that setting. In other words, as the long term trims get closer to the actual fuel adjusted amount; the short term will be closer to zero. Hope that made sense

Why I need to know:
I have a new 59mm BBTB and Stage II P&P intake installed on a N/A engine. Short term trim is high and long term is climbing. I want to use my SMT6 to adjust this back to zero trim while in closed loop mode (... under 3000rpm and/or 1/2 throttle).

I've set the SMT6 to be able to adjust the MAF values ... when setting fuel I will be cutting fuel to bring the A/F back to the ECUs setting of 14.8.

After adjusting the closed loop fuel trims to zero I can then adjust the open loop areas, and expect them to remain stable ... what do you think ??

Eldiablo owner
306 Posts
short is the on the spot correction
long term is is an average of how the fuel needs to be modify and wil laffect fueling at WOT

quick exemple..
lets say that your fue lpressure is sudently lower then usual
short term will go to +10 for the specific rpm your running atshort term will catch this and will slowly rise to +10 while the short term will start to lower back to 0

now, if you still have the same fuel pressure problem and run at a different rpm and load short term will immidiatly reset to 0 and long term will remain where it was (in this case +10)
if the +10 value is good for that rmp/load conditon then short term will remain to 0, if +10 in the long term is too much then shot term wil lgo to lets say -4
if you stay in the rpm/load spot for a while then long term will to drop until it reach about +6

when tuning try to shoot around - or +5 keep it close to 0 and the ecu will lbe happier
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