Trying to understand the DME

[thstone]

Originally Posted by Robert986

"The OEM map is static" -So, does this mean that there is only ONE fuel map used in all states of operation? I was expexting at least a separate map at WOT, giving a bit fatter mix for cooling.

You are correct, there is more than one map. What I meant by "static" is that the maps don't change. They are pre-programmed at the factory and stored in permanent memory.

Originally Posted by Robert986

The main reason for my interest is if I would be able to use the 987 MAF-tube (as a part of switch to the 987-airbox and 997 throttle/Plenum) without a re-map. Let´s say I manage to convert the MAF-signal so the voltages going into the DME represents the actual airflow.. Would that be enough? I mean then the DME would get the correct airflow into it´s calculations, the difference should be that the new intake system would allow for a better airflow, giving more air. Then I take it that the STFT+LTFT would compensate so it would all be working.

This makes sense. The question is whether stock DME has enough range in STFT/LTFT to accommodate the additional air from the 987 intake? For example, if the 987 intake flows 20% more air, the STFT/LTFT will have to be able to adjust the trims by +20%. That seems like a lot for a system that is meant for fine tuning engine operation. However, if its only +2%, that might be possible. I don't know the answers to those questions. I'd suggest searching to see if you can find someone who made that mod and ask them.

Originally Posted by Robert986

However.. Since the imroved airflow + extra fuel will give more power, would I then need a fatter mix at WOT for more cooling? Or will everything be ok?

I'd have to look at the book that I referenced to remember how the ECU handles the switchover from closed to open loop for WOT. My gut says that it takes the closed loop trims and then fattens up the mix even more (that is how I'd write the algorithm!). I'll take a look today, with the virus I'm just hanging around the house and this is way more interesting than cleaning my workshop.

[Robert986]

Thanks thstone!

I do plan to take it to the tuner for a re-map, however if one can convert the MAF-signal eg via an arduino to make it all fly, that would be neat for everyone wanting to switch to the 987 airbox/MAF-tube without having to re-tune.

[jsceash]

Originally Posted by Robert986

Thanks thstone!

I do plan to take it to the tunder for a re-map, however if one can konvert the MAF-signal eg via an arduino to make it all fly, that would be neat for everyone wanting to switch to the 987 airbox/MAF-tube without having to re-tune.

There is a signal range returned from the MAF to the ECU. This value is compared to a table for air flow so to speak, each millivolt or milliamp has a value. So the return signal triggers an exchange in the mix calculation. So in the end the signal has a range in the ECU and a maximum value in the table. The table has to be changed.