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I would appreciate some thoughts regarding the IAT compensation on an Elite.
No problem here, just brainstorming.
The engine is a rather simple 1.3ltr N/A rally engine, running on 11.2:1 CR, OEM intake and mild cams. ECU is a Haltech Elite 1500.
The Haltech ESP software has an option for auto IAT compensation, which I haven't tried yet, but I am wondering whether i should, to simplify the STFT workload.
Following Andre's advice, i am currently using manual IAT compensation of around 2,5%/10oC, for normal conditions, but not leanning it out on high IATs to avoid running lean on heatsoak restarts.
Would it bring anything if i Switched the auto correction on and zero out all the manual table, except the hot restart area? Or i am just making things more complicated with no real benefit?
Any experiences ?
The auto mode (which is common in VE based fuel models) just accounts for the air temp directly in the main air mass calculation instead of doing it in a separate table. Generally I find that this is a little over bearing and will result in particular in a lean condition when the air temp sensor is heat soaked. By all means try it, but you may find that you need to then use the IAT correction table to add a little fuel back in to the low load, high IAT region. It's all a compromise regardless which way you do it as the IAT sensor doesn't report the charge temp entering the cylinders which is what we really want to know.
Hi Andre, thanks for your feedback.
How would you define the high IAT region for such a small N/A engine?
Based on my data, on a normal summer day (25-30oC), IAT reading is around 30-40oC in normal city-high way driving and would soak up to 50oC after a shut down. In my understanding, this is nowhere close to a heat soaked forced engine intake and therefore not so critical. Based on the 2,5%/10oC rule, this should be ~5% off, referring to a 30oC base value and i would assume that LTFT would be able to work it out until IAT is back down to normal.
In respect to the 2,5%/10oC rule, could you please confirm that this is referring to oC and not oF? After a short research I came calculated this:
and i am a bit concerned.
I've just replied to your other thread so you can check there for my explanation, however in short, yes I'm talking in degrees C.
What I suggest doing is starting with an across the board 2.5% per 10 deg compensation table and then modifying the table as necessary based on the actual AFR variation. Every engine is a little different and it will depend on where your IAT sensor is located. You should be able to use the recommended 2.5% per 10 deg C change at moderate to high load, however you will probably find this needs to be reduced at idle and high IAT which is where you'll land when the engine is suffering from heat soak.