Bosch to Hitachi MAF

[Terry McLane 312.630.0533]

    >> Andrew Rabbitt wrote:
    >If 220CFM is 0V, then how is the ECU going to determine anything more 
    >than that (ie: negative volts).  The way it looks to me is your ECU is
    >limiting your airflow as much as your AFM.
    
    The voltage figures I quoted were only for purposes of example, but
    it should only be necessary to measure the air flow up to the engine's 
    peak volumetric efficiency.  This should cooincide with peak torque 
    (3200 RPM @ WOT in my example).  I assume there is no need for air 
    measurement beyond this point as VE falls off at higher RPMS. 
    In otherwords, the engine may use more air per second, but not more air 
    per cylinder per injection event. Therefore a richer mixture would not 
    be necessary.  
    
    >>Like all other MAFs, the Hitachi unit (I presume it's a bypass unit 
    >>similar to that fitted to the previous model Taurus, and many other 
    >>Fords), is non-linear and therefore a 2-point calibration will not be 
    >>adequate.
    
    You're right, I am interested in the bypass unit, due to its low 
    restriction (low pressure drop).  The air meter on my car uses a 
    logarithmic potentiomter which is hooked to a "swinging door" suspended 
    in the air stream (resistance is 200-400 ohms).  Needless to say, it's 
    very restrictive.  Having read a couple of articles on the Hitachi unit 
    used by Ford, I was under the assumption that it also used a 5 volt 
    reference and a logarithmic output.  It also doesn't require any other 
    circuitry for "burn off" like other hot-wire MAFS.  I figured that the 
    Hitachi would allow higher airflow potential so if I could determine 
    voltage output equivalent to peak torque and idle in my engine for both 
    units, they could be swapped if a suitable mapping implementation could 
    be found. As a bonus, the air meter also uses a thermistor to measure 
    the air temperature, the Hitachi adjusts for temp/pressure 
    automatically, - I thought I could hook up a trim potentiometer to 
    substitute, giving me a straightforward rich/lean adjustment mechanism.  
    Always looking for more adjustability. (I imagine the ECU is fairly 
    sensitive to air temperature in this application).  
    
    >>Also, at large throttle openings, the signal jumps around a bit, and 
    >>the only way I know of getting around this is to purposely alias the 
    >>signal by sampling synchronously at a pre-determined crank position. 
    >>(I'm assuming a digital controller)
    
    Is this at constant high flow, or sudden openings? At constant values, 
    shouldn't the closed loop mode of the ECU adjust?
    
    >>Setting this up is no easy task (speaking from experience here) and 
    >>if you get it wrong, you'll likely be out by more than 100% in some 
    >>areas of the speed-load map.
    
    Bear in mind that I have only a passing knowledge of electronics, my 
    original question was based on the observation that it should be 
    possible to build a simple circuit to map the low voltage and high 
    voltage of each unit at a given air flow, and then interpolate.  
    Obviously if there are other electronic "gremlins" present in the 
    Hitachi MAF, this may not be feasible.
     
    I'd like to talk to you direct- can you respond with your e-mail 
    address?
    
    ...Terry  tm8 at ntrs.com