shauer wrote:Yes it is quite interesting and confusing from my point of view. The MAF sensor does indicate slightly higher readings when the ambient air is cold as expected. I can easily see this at idle. My issue is that I would need to correct my calibration curve well beyond the point needed for the same exact mass flow reading when the ambient air is warmer if you follow me. For example, I may idle at about 3.5 g/s at 70 deg F but may idle closer to 3.7 - 4.0 g/s at 32 deg F but I run lean. The calibration curve values between 3.7 and 4.0 g/s would need to be increased to the point that I would be running noticeably rich at a warmer ambient air temp.
I am also in the process of getting another MAF sensor to try. Based on the data sheet, the Bosch HFM-2 has an ambient temperature sensor (thin film resistor) incorporated into the MAF circuit. I guess it is possible I have a bad sensor but it works reliability in all other aspects of operation.
There is no direct data provided in the data sheet regarding temperature response but the data sheet does have an accuracy spec of +/- 4%.
I guess my original question still stands, is the manual MAT correction curve feature available in MAF mode? If the sensor has an accuracy spec of +/- 4% and we are using old, used sensors, then why are we assuming the sensor will be 100% accurate under all operating conditions and not require some manual correction? I'm trying to search and see if OEMs sometimes add some additional correction to the raw MAF reading in their ECUs but it is difficult to locate such information.
elaw wrote:Just to toss out my two cents, and I think I've said a lot of this here before, but I've seen the same thing as the original posted. Funny thing is, I've experienced it both with speed-density and MAF. With my setup it seems most pronounced at idle - at mid and high load the tune seems pretty stable. But at idle it seems like I have to retune seasonally.
One thing that could be at least a partial explanation in my case is I'm using the factory PCV setup on my engine. So at idle, there is some "stuff" (air, combustion products, whatever other gases are in the crankcase) coming into the engine via a path that bypasses the MAF sensor. I'm also using evaporative canister purge, but that's not active at idle. Canister purge is one place I could easily see a seasonal variation, as there will be much more evaporation from the fuel tank in warmer weather.
billr wrote:Well, no doubt this is going to "ruffle some feathers", but... I think MAF is an expensive farce. For all the reasons mentioned above, a pound of air isn't processed the same in an engine at low rpm and high MAP as it is at high rpm and low MAP. The VE table that we tune isn't just accounting for the actual cylinder-filling characteristics, but is also trimming for the other factors.
sjf911 wrote:I would think the thermodynamics of airflow over a hot wire would dictate that hotter air of the same mass flow would cool the wire less than cold air of the same mass flow yielding leaner AFR's at hotter temps. Do we know if any OEM's use temperature correction?
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