11 PSI Boost for the '86 to '90 Audi 10V Turbo Engine

This roughly describes the wiring changes to bypass the factory overboost protection. THIS CAN BE DANGEROUS - READ THE CAUTIONS BELOW

Your fuel pump control relay is grounded by the ECU.  That way, the fuel
pump doesn't run if the engine isn't running.  Also, that lets the ECU
shut off the engine when the ECU sees overboost or when RPMs exceed
the programmed limit.  It shuts off the engine by opening the ground
to the fuel pump relay.

To bypass the "overboost shutoff", you just have to provide another ground
for the fuel pump relay.  The fuel pump relay ground circuit runs from 
terminal 47 on the relay board under the hood to terminal 21 on the
ECU plug.  The ECU is behind the cover in the right side of the passenger's
footwell.  The wire to terminal 21 of the ECU plug should be a brown wire 
with a greenish yellow stripe, 3rd connector from the end of the ECU plug.

If you run a jumper from the terminal 21 wire to ground, you will 
find that the overboost shutoff goes away and that your dash readout 
now reads to 1.6 bar (9 psi) or 1.7 bar (10.5 psi) - or whatever your 
spring produces.  You can probably get by with 1.8 bar (12 psi) with 
good 92 or 93 octane gasoline.  The pressure sensor in your ECU only 
measures up to 2.0 bar, cars running a higher boost than that will 
only see 2.0 bar (15 psi) on the dash readout.  You should have installed 
a boost pressure guage long before you get that high!  Plus, on a 
10V engine such as yours really high boost levels call for other 
modifications first.  You can experiment with raising the boost a bit 
by adding a washer under the spring in the wastegate.  Be careful of 
going too high and causing detonation - if this happens back off and 
go with a bit lower boost.  You can improve octane by adding toluene - 
I've got a writeup here:

    http://www.elektro.com/~audi/toluene



After adding this jumper, you should know that you have also disabled the
rev-limiter on the car.  And if the engine stalls, the fuel pump keeps
running - THIS CAN BE DANGEROUS if the engine stalled because of something
that is leaking fuel!  Like an accident!  Be sure to shut the key off
if the engine stops.

You can build an added relay circuit with a second oil pressure idiot 
light switch controlling it.  This circuit should only connect your new 
ground circuit through the added relay when the engine is running and 
has oil pressure.



These instructions are offered at no charge.  
Use them at your own risk.


I am not responsible for any damage or problems associated with use
of this information.  If you use these instructions, you are doing it 
on your own decision to so, and you must understand the implications.  



    - Charlie











 
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