Running out of fuel on your 240 turbo with CIS?  At about 12 psi, the average 240's Lambda system starts to let the engine run leaner and detonation can occur.  This can 'easily' be solved by adding a 5th injector controlled by an Additional Injector Controller (AIC) or just changing to a full EFI system.  These solutions start at $250 for an AIC and can run over $1000 for a stand alone EFI system.  If you are looking for something a bit cheaper to squeak a few more psi out of your CIS system, then consider the 'terminal 11 trick'.

Under non-boost conditions and up to 3 psi, the Lambda system varies the duty cycle of the frequency valve on the fuel distributor to control the air/fuel (AF) mixture based on the O2 sensor.  The duty cycle varies as the computer tries to keep the mixture at stoiciometric (perfect mixture).  The lambda system has built in logic for enriching the AF mixture while under boost.  The 'pressure' switch that is mounted on the engine compartment triggers at 3 psi and causes the frequency valve to run at 70% duty cycle by grounding terminal 7 on the Lambda computer, thus enriching the mixture. By grounding terminal 11, you can get the duty cycle to go to about 90%.

Parts Needed:

• An adjustable pressure switch with normally open contacts.  The Saab overboost switch from any 80s turbo is an ideal switch for this application.
• 2' min length of 14 gauge min wire with connector for Lambda computer.  It is easiest to go to a 'u-pull' auto parts yard, open up a Lambda main connector and remove a connector with a length of wire attached to it.  The connector is easily released from the main connector by depressing the small locking tab on the connector with a paper clip or dental probe.  If your car is a factory intercooled (84.5-85) you do not need this wire because terminal 11 is already 'connected'

The switch seems to be originally set to come on at 14 psi and turn off when the pressure returns to 11 psi. There are normally open and normally closed contacts.  The main screw adjusts where the on/off range is and the smaller screws adjust the width of the on/off range in relation to the main adjustment.  It is easiest to perform initial pressure set points with the switch out of the car.  Note:  The numbers on the pressure switch shown have been marked in black to highlight their location.

Terminal #1:       common
Terminal #2:       normally closed
Terminal #3:       normally open

Screw #1 'average pressure range'
    CW = higher switching pressure
    CCW = lower switching pressure
Screw #2 'upper range'
    CW = decreases the upper switching point
    CCW = increases the upper switching point
Screw #3 'lower range'
    CW = decreases the lower switching point
    CCW = increases the lower switching point

By adjusting screws #2 and #3 an operating window can be set around the average pressure setting of screw #1.  A range of 1-2 psi is recommended.