87.5 CGT Trip computer & MC swaps, do they get along?

Tony Lum tlum at flash.net
Mon Jan 12 19:07:36 EST 2004

At 04:38 PM 1/12/2004 -0500, Huw Powell wrote:

>>Has anybody gotten the trip computer in the digital dash of a 87.5
>>CGT to work when a MC swap is done? More specifically, when an MC
>>swap with 034EFI is done?
>I doubt the latter could be done, since it appears that one of the inputs 
>to the trip computer comes from the CIS air plate potentiometer.

I think that the orange display from the 87.5 will work.  After all, the 
same display was used on later urqs.  In fact, the CIS air plate pot is not 
hooked up on the orange displays.  I went through this when I first got my 
87.5 CGT.  It had an red display which I knew was not original because it 
had sky blue marking "87 coupe" on the top of the IC, just like they mark 
parts at the pick and pull.  Further investigation showed harness wires to 
be missing-those that run to the CIS airflow pot.  What the h*ll!  So I put 
those wires in and the IC still read 15.6 MPG.  I was about to give up when 
Wolff (turboquattro.com) got a nice black 87.5 CGT.  That car was having 
some fuel problems (which a fuse in the right location mostly fixed ;^) but 
it had a working trip computer.  Imagine my surprise when I checked the 
wiring and found the exact same wires were also missing from his 
harness.  I also noted that his display was orange, not red.  I later found 
out that the 87 M.Y. cars used the CIS-E fi while the 87.5 coupes were 
CIS-E III (2.3L).  I removed the extra wires and got an orange display from 
Chris Semple (www.force5auto.com) and the trip computer's worked ever 
since.  28-32 MPG, I love it!  Plus the dull red display would make me 
sleepy :(

So in summary, the orange digidash was used in 87.5 CGTs and later 
urqs.  Steve Eiche (who is constructing a RR euro urq) has noted that there 
is an addition switch mounted on the PCB for the digidash which may 
compensate for the additional fuel a turbo engine would use.  But for the 
most part, the orange digidash only needs speed and fuel level to calculate 
fuel consumption and does not require either the airflow pot OR the fuel 
enrichment signal from the ecu.  Neither is provided for on the urq.  One 
little extra note: the connector used on the digidash is the same one used 
on type 44 autocheck ecus.



Tony Lum                                  1987 5000CS Turbo Quattro
Berkeley, California, U.S.A.                1985 4000CS Quattro
Audi Owner/Driver/Mechanic by Necessity ;^)   1980 5000S Sedan
                                                1987.5 Coupe GT
                                                 1983 Ur-quattro

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