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Air Temp Compensation

EFI Tuning Fundamentals

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In the fuel compensation module, with respect to intake air temp compensation, it was stated that we need an arbitrary zero point where no fuel compensation done. Normally 15 or 20 deg C. This is where I am a bit confused and would like clarification.

Assuming I am tuning based on speed density using injector pulse width tuning ( not VE, so no air temp consideration). Shouldn't my zero point be at the intake temp my tuning was done at?

For example. If I am tuning my map on the dyno and the intake air temp was 30 degC at that time, seeing that my injector pulse width was tuned at that temp for my desired afr, should I not use that temp for my zero compensation point?

If the temp compensation is a linear compensation, you can tune at any temperature -- since it will be compensated...

Tes, it is just a datum temperature to add or subtract from. You can really use any temperature but 20C is a common standard, and if comparing maps with other people, or vehicles, it means you don't have to correct the corrections.

Guys correct me if I am wrong, but I would say:

- If you have already tuned your car without compensation, and then you want to setup that IAT fuel compensation table, I would use as the 0 point the temperature that was ambiant during the tune.

- If you setup the compensation table before tuning the fuel map, then I would use 20°C as a standard 0 point, but it does not really matter in fact.

Thanks all for the replies. I was also thinking along those line Martial. But another question I would like clarified if you all could. With the speed density method (without VE tuning). It was mentioned that IAT is not used in the density equation. So I as assuming the ECU uses standard temp 519R and uses the MAP reading for Pressure to calculate density and then compensates for temp, based on the compensation table?

So the equation 2.7(P/T) => the T would be 519R and the P would be MAP?

Am I understanding correctly?

Bearing in mind it is almost 4am local time...

Pizza, yes, if I read you correctly - if one forgot to set a datum temperature, you will need to work from what it was defaulted to, but it's preferable to have a 'standard' temp.

Corbeau, again if I read it correctly, the inlet temperature to the turbo/supercharger may not be directly relevant as it will be altered by the compressing and any charge cooling, so it will be measured at the manifold.

Ok, so trying to figure out my pulse width at say. 6000rpm, WOT @ 10psig of manifold boost pressure.

The respective air density at that cell would be 2.7(24.7 / 519)? Ignoring IAT for now.

I am correct in my assumption?