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>Subject: Chip / zener diode for boost adjustment
>Spent several hours manually looking through the archives for this, to
>no avail. I'm looking for instructions and which parts to use to allow
>higher boost without defeating the fuel pump overboost shut off. I just
>recently purchased a 1.8 spring, and am reinforcing the IC, and
>replacing all the turbo hoses (air, oil, and coolant).
I blew the intercooler soon after, the hose four months later...
>I know that this can be done with a zener diode, and a resistor (it
>think that was the parts list), or by reprogramming the ECU. Could
>somebody please contact me off the list if they have the directions for
>the cheap fix; or if anybody has would have the code and be willing to
>burn me an EPROM. I am comfortable with putting a chip socket in my
>MAC-11, or any other electronics operations. Sorry for the waste of
I did the cheap fix more than two years ago, works great. Used a micropower
voltage reference instead of a zener, the leakage current was less than
one tenth that of the best zeners I could find. I still have a few in a plastic
bag somewhere. I can probably also send you the resistors to get 1.8 bar
from my grab-bag of loose parts.
Now for the hard part, I've forgotten where/how to put them in......
( they say memory is the second thing to go )
I have it wired so the dash meter reads correctly shows the boost
going smoothly to 1.8 ( GOT to have the stiffer spring for the smoothness).
Three cuts to traces on the main board, add the reg. + three resistors,
let me think about this some more, let me know if you decide to
go this route. Personally the EPROM is the better choice, because
the ignition timing advance is not advanced when the high (1.3+)
boost kicks in.
'86 5kQ ( soon to have new timing belt )