[urq] ECU replacement

[CARDCONSYS at aol.com]

        Steve, I completely agree with you on the question of re-engineering 
the MAC02 and its variants. As you point out there are proprietary components 
such as the hybrid assemblies and the obsolescence of many parts. I know 
having tried to get just information from Hitachi USA myself. The pressure sensor 
module would be the easiest to replace with a Motorola/Freescale part and a few 
parts to duplicate the output of the Hitachi unit, if someone has it 
accurately mapped. Even that would not be trivial but if someone has the exact 
pressure in to voltage out transfer function I may be able to put something together 
to be tried. As for the rest, laying out the PCB would be relatively easy, 
compared to the monumental  design effort required using new components and 
completely new software. Never ever worth it. Cheaper to transplant a 3B!
       Just to indicate how many ECU variants there are I have an ECU from 
Jim Furdyn from a 1984, KG engined, Audi 200 Turbo. This is a Bosch unit using 
an Intel 80 series processor and a Motorola SPX3025PCA pressure sensor mounted 
on a small daughter board with an amplifier and a hybrid resistor assembly. It 
appears to have many more components than an MAC02. Am taking a look at it to 
see if the sensor assembly is worth looking at as an 'UrQ' replacement.
       By the way, I suspect that the failure of the output transistor 
driving the frequency valve may well be due to external factors. The wire from the 
ECU to the valve should have a deliberate resistance of around 12ohms. If the 
harness is modified or this wire replaced it would cause overloading.
       Our best bet as a group is simply make sure we understand completely 
how the MAC02's work and their modes of failure and improve the knowledge base. 
We may then be able to substitute individual weak parts
       Just my tuppence worth.
       Martin Dapot
       Cardinal Control Systems, Inc.
       Herndon, VA