Re: TAP Chip & WG Spring in '90 200Q

["Scott M." <scottmo@teleport.com>]

Michael,

You said:
> Yesterday my local Audi specialist (Eurosport in
Merrimack, NH)
> received the chip and wastegate spring from Total Audi
Performance.
>  They proceeded to install them both into my
recently-purchased 1990
> 200Q. Here is a rundown of what I have experienced so
far:
> 1) The wastegate spring, once installed, caused the
engine to shut
> down completely above 2000 RPM. The mechanic at Eurosport
said that it
> would take roughly two hours to tweak the wastegate to
make it work
> properly. They said that it's the same problem they had
with a TAP
> upgrade they installed in an S4 recently. I was under the
impression
> that this was a plug-and-play operation. (Plug and Pray?)
<Snip>

I took a look at a TAP modified MAC11 ECU from a 1987
5000TQ awhile back and found the following info. 

Disclaimer: I don't know when this ECU was modified by TAP
or if they still do this type of mod on the MAC11 or on the
later MAC14 ECUs. The owner of the car using this ECU
indicated that the car ran very well with lots of power and
no fuel pump cutout.

After opening up the ECU, I found that they used a Zener
diode and a series resistor to reduce and clamp the output
from the stock pressure sensor. On the ECU I had, the zener
was soldered across two pins on top of the pressure sensor
hybrid circuit and the resistor was installed between Pin 1
on the sensor and the main circuit board. This Zener had
the effect of altering the pressure sensor output voltage
to effectively raise the boost map setting the ECU would
make, to  around 1.75 bar with the stock waste gate spring.
The TAP spring I looked at would make about 1.95 bar on its
own without any ECU assistance.

When viewing the operation of the WG solenoid using the LED
test light and the stiffer TAP spring and modified ECU, the
computer would give up adding pressure to the top of the
Waste Gate diaphragm pretty quickly because with the Zener
mod it was only trying to make the 1.75 bar value and with
the extra tension of the stiffer WG spring the ECU
assistance was not needed. The EPROM chip out of this ECU
had all the timing values in the two timing maps changed by
1 degree and had no other changes. On this ECU when I
tested the overboost fuel pump cutoff, I could not get it
to operate even though I applied ~2.6 bar. 

If your stock boost gauge reading is off, then they may be
using a similar mod to the one described above. You can
test the overboost fuel pump cutoff feature and find out
what boost level  it cuts out at by doing the following: 

With the engine warmed up, shut off the engine and connect
a hose from a hand pump (bicycle pump works great) to the
ECU pressure/vacuum hose port and a tee connected to an
accurate analog boost gauge. Plug the hose coming from the
engine intake and start the engine and run it at ~ 3000
RPM. Slowly pump up the pressure while watching the boost
gauge, with a stock ECU setup you should see the overboost
fuel pump shut off the engine at around 1.6 bar absolute or
about 8.7 psi gauge pressure. You can also look at the
stock boost gauge and get some idea as to how much
difference there is between the analog gauge. It could be
there was a problem with the installation of the mod, as
others have mentioned you may need to return it to TAP for
corrective action.

HTH
Scott Mo.