Bosch MAF to Hitachi MAF

[tom cloud]

>    Is there an easy way to invert the voltage signal from the Hitachi to 
>    the ECU?

                 +------R2----+
                 | |\         |
      in --- R1 -+-|- \       |
                   |    \_____|____  out
                   |    /
                +--|+ /
                |  |/
                R3
                |
        (gnd)--pot--(max offset)

Maybe simple op-amp inverter (LF-351, LF-356, uA-741).  For single
supply (i.e. if running too close to 0 or plus 12) use one of LM-324.

Adjust the (inverting) gain with R2.  Z-in is set with R1.  R3 can
be zero.  The pot will allow for an offset, if needed.

For example, if present app output is 0 to 4 volt, and want 4 to 0,
feed output of sensor into R1 and set gain = -1 by making R1 = R2.
Consider that the output/input are like a see-saw centered on the
offset voltage set at the pot.  So, since you want 4 in to make 0
out, set the offset at 2 volts.  Then, 4v in = 0 v out, 2 v in
= 2 volts out, and 0 volts in = 4 volts out.  Voila'.

tom