ADDING KNOCK SENSOR IGNITION

If you've increased your compression beyond approximately 9.2:1, or you've added forced induction to your vehicle, you've no doubt noticed the pining that you experience if you aren't burning 91 or 93 octane gasoline.  You've also probably retarded your timing to TDC and run your spark plugs back a couple of notches in temperature just to control detonation.  These are all things I had to do to keep knock under control with my turbocharged engine.  These are all steps that decrease power output even if they do solve the problem of detonation.

Volkswagen solved this problem with the 1985 GTI by adding a knock sensing ignition system.  This system has a knock sensor attached to an existing bolt hole location on the front of the 1.8 liter block that is attached to a black box computer that continuously adjusts timing to compensate for various grades of gasoline, etc.  This enabled the 10:1 compression ratio 1985 GTI engine to run on regular unleaded gasoline.

Another good location that describes this swap is at driversfound.com.
A good VW Vortex thread is HERE.

After finding a 1986 GTI in a local salvage yard, I was able to locate all the parts I needed to install a knock sensor on my 1984 GTI

If your car already has electonic ignition, you will need:

If your car has points ignition, you should also pick up:

Usually the knock sensor is deteriorated to the point where it should be replaced.  New ones are readily available for about $60.  The older knock sensors, or "Type I" sensors, are rectangular in shap with the wiring entering at a 90 degree angle.  The newer "Type II" sensors are more rounded and the wiring runs straight into the unit.  The type II sensors come in "green" or "black."  The only difference I can find between the two is the length of the wiring pigtail.

Installation is a simple bolt-on.   You will find an unused bolt hole on the front of your block located on the right side of cylinder #1, which is where the knock sensor bolts on.  Because of all the accessories on the front of the engine, it's not necessarily the easiest place to get to with a wrench though.   Your existing cap and rotor will work fine, which means you can use your existing spark plug wires.  The cap and spark plug wires from the A2 GTI are different than the ones used on A1 vehicles, so if you go with the A2 cap, you'll need the plug wires as well.  I simply popped the noise suppression cover off the A2 cap and slid it on my A1 cap - it's a little loose but works fine.  The knock sensor itself should be torqued to 15 ft-lbs.

The most complicated part is the wiring, and fortunately several of the posters on VW Vortex have done the work for you.  Here are the necessary wiring diagrams.

One item of note, the TBerk color wiring diagram shows pin 10 connected to current track 50 (hot while cranking) at the starter.  This is not necessary - this pin should be connected to ground as shown on the other two diagrams.  The green wire to your existing ignition module is attached to the green/white wire to the knock box.  The yellow wire to the knock box and the throttle body switches can be sourced from terminal 15 on the coil.  It is a good idea to had a fused link for this connection.

Retention of the idle switch is important if you want to retain a smooth idle.  This switch tells the knock box to ignore the vacuum port and to keep the timing static.  Without this switch, your idle will wander and your RPMs will drop drastically when you first lift off the throttle.

If you have CIS lamda, you have a wide open throttle switch on the throttle body.  This switch places the oxygen sensor/frequency valve feed back loop into open-loop operation, which richens the mixture for full throttle sprints.  The knock sensor system also has a wide open throttle switch, and both switches should be retained.  Problem is, the lambda switch is on the ground leg of the circuit, while the knock sensor switch has 12 volts running through it.  This means you can't splice the two switches' wiring together.  The easiest thing to do is stack the two one on top of the other as in the photo below:

All you need is some longer screws - M3-.5x40mm or #4-40x1.25" will work fine for this task.  I had to drill two new holes in the mounting bracket to lower it down sufficiently for both switches to be activated by the throttle linkage.  

If you have a Neuspeed throttle body, it has all the mounting points for the A2 WOT and idle switches.  If not, you will need to use the throttle body from the A2 donor car.  You will have to swap linkages with your existing throttle body, and the idle stabilization valve opening will need to be plugged.  These are trivial issues that are easily solved.  

The wiring can be dressed through existing grommets that pass from the rain tray into the engine compartment.  I used the existing grommet that was used for the ignition module and hall sender wiring, I just had to widen the opening somewhat to accommodate the larger number of wires for the knock sensor setup.

A good location for the knock box is on top of the blower motor cover.  I simply attached mine with some velcro so I could move it if anything requires service.  You can also mount it behind the ignition module on the driver's side of the car (in the rain tray), but this requires some drilling of holes that could allow water to enter into the cabin and contaminate the fuse box, therefore I elected not to go this route.

On A2 vehicles the idle switch is usually shot.  The plunger that activates the switch is held in by a rubber grommet, which disintegrates over time and allows the plunger to fall out.  If this is the case, you must purchase new switches, which cost about $90.

Here are some helpful part numbers: