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Procedure for calibrating air flow meter.

Practical Diesel Tuning

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Hi all,

I'm wondering how i go about correcting the calibration of the airflow meter on my Hilux running the Motec diesel package.

I have modified the intake system and installed a AFM from a ford ranger. I do have the calibration table for the sensor that was provided from Motec however I'm not using the for intake tract and the sensor is installed in the downpipe to the turbo intake.

The pipe i used is the same internal diameter at the factory ford airbox so the cross sectional area should be the same.

What technique should I use to validate the calibration and make the necessary corrections.

I was considering re installing the factory AFM back in the airbox and using it as a reference but it will only be good to a certain point at it wont read high enough.

If anyone can shed some light on this that would be fantastic.

P.s. I want to try and the AFM cal correct so i can try and get the injector linearization table corrected.

Cheers John.

You could use the factory one and dial in your injectors based off that until you run out of AFM, then swap to the ranger unit and work backwards, calibrate the AFM from your injectors as much as you have them calibrated. After that you could do a bit of scaling and trial+error to dial in the higher load stuff.

Thanks for the reply Ben,

This was what i was also thinking. Im currently running a K&N air filter in the factory air box but wonder if this will affect the factory flow rates as well. I also made a custom pipe from the airbox to the turbo to get rid of the factory rubber one and to fit the for AFM. I have the option in the motec software to use a second AFM as a reference so this might be the easiest route.

The filter may increase airflow into the engine, but shouldn't effect how the meter reads that are as such.

That is one option, have both AFMs on at the same time so you can get a direct comparison. A little complex but should be fairly accurate.

Yes that's my thought exactly.

I have wired the factory one in again temporarily and set up a custom screen so that i can make the required adjustments.

I hope to get out and start the process today.

Ok so i have Aligned the ford sensor pretty accurately with the factory toyota sensor but im sure there is still error in the system. Is there a method of calculating the inlet mass from afr. I did some maths and created this formula. (lambda value * 14.5 ) * Fuel mass = engine charge in mg. This seems to translate to some degree but to get to g/s the formula seems allot more complicated. I can only assume that the injector linearisation tables are close but there is no real way to prove this unless i know the air mass reading is correct.

Any way im going around in circles.

If there are any suggestions please let me know



I have spent a couple of hours this afternoon trying to figure out the maths and make a reverse calculation that uses fuel mass and lambda and rpm to calculate g/s i have attached the excel document below.

Attached Files

Nope this doesn't work either.

I think the only way to get this right is to try and get the whole setup on a flow bench and create an entire new calibration.

Is it an option to just "go by feel". Wind the boost up and add fuel to suit? I know it's not ideal but if you spend the time on it, realistically the end result will still be a car that drives fine and makes good power safely. Even if the numbers in the tune don't line up perfectly.

This is how i have been doing it up until now. But not having everything correct is triggering my OCD haha. I just want to create the best tune that I can.

First of all try to get away with a MAF sensor if you can. I never used in combination with an aftermarket diesel ECU with the exception for R&D to perfect the VE model still running MAP for main calculations.

If the MAF sensor calibration is unknown a easy way is to place the new MAF sensor inline with the air intake system and use a spare input on your ECU (if there is any) to record the sensor reading. Second option is to use a datalogger and record both sensor signals.

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