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Audi Coupe 2.3 20V Quattro 1991

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  • Audi Coupe 2.3 20V Quattro 1991


    I'm currently the proud owner of an Coupe 20v Quattro.
    It is one of my dream cars (All of them are Audi's), I'm currently working on modifying it with some newer features such as; Cruisecontrol, Electric Climate control, Upgraded central locking, Autocheck with consumption meter, outside temperature display and 5x112 conversion. (I'm also working on some experimental mods like comfort windows). I work alot so I barely have time to work in it so I will try my best to post here!

    Cruise Control

    This is from an Audi 80 but the components are basically the same.

    Combined Switch

    Since it's a 1991 model I still had the old style stalks but I wanted the newer ones because of the cruise control, moving the hazard light to the dash and for the controls of the autocheck.

    I used a wiring harness from a newer 80 since the original wiring harness was beyond repair (Alarm and "vandalism") but it is possible to convert the old style combined switch connectors to the new ones.

    I got the Autocheck with fuel consumption meter from a fellow Audi enthousiast with the newer type stalk: 4A0 953 503 A but this was one didn't have the stalk for cruise control and was also really hard (expensive) to find therefore I used a A4 B5 combined switch 4D0 953 513 P and took it apart. Apparently the stalk they used is exactly the same as one from an 80 B4. If you take the 2 halves apart and remove the cruise control stalk. There is a small metal pivot that you can remove with a nail if you do the same with the 80 stalk you can recombine them and have the cruisecontrol stalk on your combined switch. The only issue is that the original combined switch has an inverted connector and because of that you can mount the connector on the combined switch but if you order the OEM connector you can swap the pins (same pins) and have it mounted the OEM way.

    Control module

    I used the control module from an A4 B5. 4D0 907 305 (5GA 004 397-16) This module looks and functions the same as one from an 80. The only difference is the pinout. Audi even used the same color wiring. You can use all the parts except for the mounting bracket from the actuator and from the vacuumpump.

    The arm on the actuator is shorter than needed for an 80 so I am going to make my own soon.

    Wiring and sensors

    The sensors are the same as most old Audi's. You need 2 of them one for the brake pedal and one for the clutch pedal. The vacuum line connecting them is too short but any line can be used.

    The vacuum pump / actuator is 811 907 325 and has the same functions as the original one from the 80/90.

    The wiring is pretty simple. I took the wiring from an A4 B5 so I made a stand alone plug in wiring harness. and connected them like you originally would.

    Here is a document showing how to retrofit cruisecontrol. gra.pdf It is in german but with the help of google it is usable.

    Upgraded Central locking

    The Coupe had the stock central locking pump without the remote.

    I took apart a A4 B5 and took the wiring harness, I got the pump from an S8 D2.

    The pump (8L0 862 257 G) supports 433.92Mhz remote and DWA. I'm not going to install DWA (Diebstalhanlage) since I don't see a reason for it.

    The wiring harness is quite a mess but back in the 1998 days they used multiple harnesses to make up a combined harness unlike now where it's a big mess of wires. After removing the unused wiring I was left with the central locking wiring harness. Since my Coupe does not have an anti theft alarm I don't have the microswitches in the cylinder locks. After looking at the forum page from user "Mdz" I thought I could use the locks from an A6 C4 with AAH keys but the bootlock is different from an A6 compared to a Coupe. This conversion can easily work with an 80/90 B4.The microswitches in the cylinderlock were original with some 80/90. The A4/A6 also have microswitches in the doorlocking mechanism something the 80/90 also do not have. The microswitches are in place to let the Central locking pump know the door is open and also to activate the footwell/doorlighting. The microswitches are not necessary since the 80/90 have door contact switches these are basically the same thing.

    Here is a wiring diagram A8 Central Locking.pdf of an A8 which is the same as an A4 B5 but the A8 also has the "G" pump and a solenoid for opening the boot with a button. I couldn't find any A6 C4 parts therefore I looked for the alternative. The A4 B5 used the same doorlocks as the A6 C4 and these can be fitted on an 80/90 but you will also need the door handles since the AAH locks are bigger. The A4 B5 was also made with the old style AH key so you might be able to switch the lock cylinders/barrels and have the original key from your car work with the central locking.

    On Aliexpress you can buy key blades that have the AH profile and fit in the newer type flipkeys.
    This document contain basically all info Umbauanleitung_komplett1.pdf

    The bootlock and the ignition lock from a A4 B5 are different from an 80/90/A6/A8 and cannot be used. You can use the bootlock from an A8 as replacement. The ignition lock from an A6 is similair to that of an 80/90 but might be longer. I have tried to fit the A4 B5 lock cylinder in the 80/90 ignition switch but there is a size difference.

    Ambient temperature sensor

    I also got the temperature sensor from an A4 B5 and used the tutorial from user Jas11n
    Here is a link to his post: Link to ATD forum post
    I still can't find a display but I might be able to build/mod a A4 B5 one.

    I'll have to continue this topic later and I will post some photos since i'm short on time (as usual)
    I can make a tutorial how to modify the combined switch if there are people interested. ( I will try to make one ASAP)
    I'm sorry if this post is a mess but i'll try to keep it readable.

    Special thanks to: MDZ, Jas11n and M2ki
    Attached Files
    Last edited by matthew071998; 11 September 2023, 22:32.

  • #2
    I also have an Coupe 91' 20v Quattro so I'm interested in a tutorial !


    • #3
      Originally posted by pfi View Post
      I also have an Coupe 91' 20v Quattro so I'm interested in a tutorial !
      If I have some time next week i'll make the tutorial with the a4 combined switch.