MAF - Would I notice the difference ....

[mr brightside]

I'm not sure what the abbreviations you're using are.
AFM- air flow meter?
AFR- air flow rate?
Does this mean you are designing a system to measure volumetric flow rate rather than mass flow? If so are you having to find a way of compensating for altitude and temperature? It all sounds very exciting to me, you must be good with electronics!

 

[Southloop]

AFR = Air/Fuel Ratio

 

[mr brightside]

ORIGINAL: barks944

I might add closed loop AFR control.

Presumably this would mean the new system would require a Lambda Sensor which our cars currently don't have, or would you be using the new air flow meter as the measurement element and somehow using your gizmo and the DME for comparison and correction?

 

[barks944]

Sorry for the use of acronyms .

Yes it would need a Lambda sensor, I have a wideband sensor which shows my AFR (air fuel ratio) on a guage in my dash. I have a spare output from this I could feed into the MAF (mass air flow) converter.

The principal behind the whole MAF converter is to get the benefits of the modern techniques and hardware for measuring air mass flowing into the engine. These include faster response times and less flow restriction. However a MAF sensor reads air mass as you say and the 944's standard DME is designed to read an air flow signal. This makes the signals from MAF sensors fundamentally incompatable with the 944's DME. To use a MAF sensor to drive the 944's DME the mass air flow signal outputted from the MAF sensor needs to be converted to air flow rate and sent to the DME in a compatable format. This means that air density must be known to convert the mass flow into volumetric flow as you rightly pointed out. I use air temperature and sea level air pressure to calculate air flow from the MAF sensors output. This requires you to know what output voltage the MAF sensor gives for a given air mass. Once you have worked out the air flow rate you must output a voltage to the DME that represents that air flow rate. This requires you to know what voltage the original air flow sensor outputs for a given air flow rate. Once you know this you can output air flow to the DME which it will then turn back to air mass using air temp and inject fuel accordingly.

If the MAF converter also knows what AFR is going into the engine it can adjust the air flow rate to achieve a given AFR. Effectively you will tell the DME that there is a different volume of air going into the engine than there actually is. In fact this is happening all the time due to innacuracies. There are a number of issues with doing this such as dealing with cold start compensation, I would probably only enable closed loop AFR after a certain ammount of running time and with a stable air flow into the engine such as when cruising.