B4Lamb wrote:

I would not say I am knowledgeable about these things Rickydodah. I'm a retired design engineer but I was not in the motor industry. My thread started with me trying to work out if my MAF sensor was faulty as the fault code may suggest and I have learned a lot in the process thanks to the help of others on Defender2.net. Your questions about prediction.... I used that term purely in the context of knowing approximately what the MAF sensor should roughly be measuring for a set of conditions so that I could see if in practice this was achieved. In engineering you need to understand what you expect before you embark on physical experimentation. Modelling and calculations can often get you 90% of the way in a lot shorter time rather than trial and error. It may well be possible to do calculations on the fly using engine revs and turbo speed/pressure to calculate the air volumetric flow rate for a particular sized engine but I guess measuring it at the input side after the air filter is the way it was done traditionally and is probably a fairly bomb proof way of doing it hence why this is the method used by most combustion engine manufacturers.

Re your other questions I am at 420 ft above sea level and the temperature today was about +12C The slightly lower air density at this altitude would have a minimal impact on the cooling effect of the hot wire element in the sensor (slightly less cooling effect) and the low (ish) temperature would tend to have a slightly greater cooling effect compared to +25 C that may be the calibration temperature of the sensor. I think these are in the noise though.

Regarding temperature though you may recall that when I measured the voltages I established that the temperature sensor element on the MAF sensor appears to be indicating much higher temperature than actual. I would guess that the measured temperature is not used locally in the MAF sensor to compensate the measured volumetric air flow rate but that this is done in the ECU. Now if the ECU thinks the air is much warmer than it really is it may be overcompensating the MAF sensor reported flow rate and this may be why error code P1103 'MAF in range but higher than expected' is being generated. Its a long shot.

I can correct the temperature measurement temporarily by using a pair of resistors to form a potential divider and force the voltage sent to the ECU to be more representative of the actual temperature value. So I will turn my attention to that. Ideally I would like to borrow a known good MAF sensor to do direct comparisons.

Thanks for your explanation, I find this a most intriguing subject. Personally I've never been a great fan of this type of flow measurement, Lucas with their "hot wire" couldn't get it right thirty years ago as there were purely too many variables for which this type of device couldn't reliably calculate, admittedly processing of sensor outputs has improved incredibly in that time, maybe the improvement in data from other sensors around the engine and not processing data from just one source, as it was then, has improved overall performance. However good luck I'll look forward to the outcome  I started with nothing and still have most of it left!