axl911

In my quest to understand the DME of this car, I have two more questions:

1. How does the DME take intake air temperature into account in its operation? Does anyone know how it tweak the fuel + ignition map? A graph would be nice.

2. Does the DME run in open loop for fuel and ignition upon first startup (still cold engine)?

This is for a '95 model with the M2.1 Motronic.

thanks,
anthony

Stealth 993

1. It will adjust fuel & timing vs IAT. That is what the temp sensor is for. Their are many maps, & other sensors that will change with it, like head temp sensor, O2, & others. I do not know if it's a linear thing or not. I know that the lower IAT the more ignition advance you can run & also add more fuel, = more HP.

2. Yup, usually for 2min or so.

trophy

AS Stealth mentioned it does use it to adjust the ignition timing and generally low temps more advance is possible giving more HP. IAT is very important in Super or Turbo charged engines as the IAT's can rise very quickly robbing HP. As our cars use a MAF the ecu is not as reliant on the IAT sensor as say a car using MAP sensor. The IAT ignition and Fuel tables in the motronic are an 'overlay' table meaning when it is outside normal operating ranges it will adjust timing to protect the engine.

In MAP based cars the IAT sensor is very important as MAP + IAT are used to calculate load and air volume through a calculation. MAF cars measure this through the MAF sensor so are not as reliant on IAT.

THe motronic uses (as stealth has mentioned) O2, Head temp etc to do the same thing, to provide an overlay when outside normal operating limits.

Sal Carceller (scarceller) here and on Pelican has "decoded" the data in the Motronic 2.1 and others. I know he has tunned his own car himself my modifying his own chips. Would be a good guy to chat to.....

axl911

Interesting.

I was thinking on a turbo/supercharged car, would it be better to locate the AIT sensor behind the intercooler instead of at the intake to get a true reading of the now boosted/raised air temperature.

trophy

It would be good to have one before and after the intercooler to see how efficient it is.

If you only have one IAT sensor it needs to be after the intercooler to ensure it is measuring the air ingested into the engine, if it is before it could read low and could have the ecu advance ignition when infact it should be retarding....

axl911

That is what I am thinking.

Just want to verify that if the DME sees the higher AIT, it will retard timing.

That is correct?

Anyone know by how much per 10 degree temperature?

Felix

The IAT sensors on turbo and NA cars are quite different - turbos use a much faster reacting sensor because intake air temp can change rapidly as boost builds and/or the intercooler gets heat saturated.

On a NA car the IAT is more likely to be used to determine fuelling and the knock sensor used to back off timing.