Volkswagen Front Wheel Drive 1974-1989 Repair Guide

CIS/CIS-E Engine Controls

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TESTING



Control Pressure Regulator

See Figures 1 and 2

The control pressure regulator is designed to provide a richer fuel mixture during cold engine operation. When the engine is cold, the valve in the regulator is open. This reduces the pressure on the control plunger in the fuel distributor, which in turn provides a richer mixture. As the engine is running, the bi-metallic strip is warmed by a heating element in the regulator. This will eventually close the valve in the regulator and increase the pressure on the control plunger. As pressure on the plunger increases, the mixture leans out. The control pressure regulator is found only on CIS equipped engines.

  1. Unplug the electrical connector from the regulator.
  2.  
  3. Measure the resistance across the terminals of the regulator (not the connector). It should read approximately 22 ohms. If not, replace the regulator.
  4.  



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Fig. Fig. 1: Checking the heater coil resistance of the control pressure regulator

  1. On vehicles without electronic ignition, unplug the center wire from the distributor and ground it. On models with electronic ignition, unplug the connector from the Hall sending unit on the distributor. This will disable the ignition system.
  2.  
  3. Measure the voltage across the connector terminals while an assistant cranks the engine. There should be at least 8 volts displayed. If not, check the wiring for shorts or opens.
  4.  



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Fig. Fig. 2: Checking the voltage supply to the control pressure regulator

Throttle Switches

The throttle switches are used on CIS-E systems and are mounted on the throttle body. They send a signal to the control unit when the throttle valve is at an idle or wide-open throttle position.

  1. Unplug the connectors from the throttle switches.
  2.  
  3. Connect an ohmmeter to the idle switch terminals. With the throttle closed, there should be continuity. With the throttle valve open, there should be no continuity.
  4.  
  5. Connect an ohmmeter to the full-throttle switch terminals. With the throttle closed, there should be no continuity. With the throttle valve approaching wide-open throttle, there should be continuity.
  6.  

Coolant Temperature Sensor

See Figure 3

The coolant temperature sensor is found on CIS-E systems. Since its resistance value changes with temperature, it allows the control unit to determine if the engine is cold or warm.

  1. Unplug the coolant temperature sensor connector.
  2.  
  3. Connect an ohmmeter across the sensor terminals.
  4.  
  5. Compare the reading with the graph.
  6.  



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Fig. Fig. 3: Coolant temperature sensor resistance chart

Thermo-Time Switch

See Figure 4

The thermo-time switch, used on CIS and CIS-E systems, determines the amount of time the cold-start injector is on.

  1. Make sure the engine is cold. The coolant temperature must be below 86°F (30°C).
  2.  
  3. On vehicles without electronic ignition, unplug the center wire from the distributor and ground it. On models with electronic ignition, unplug the connector from the Hall sending unit on the distributor. This will disable the ignition system.
  4.  
  5. Unplug the connector from the cold-start injector. Connect a test light across the terminals of the connector.
  6.  
  7. While an assistant cranks the engine, record the amount of time the test light stays on. Compare the time to the graph.
  8.  



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Fig. Fig. 4: Thero-time switch ON time graph

Idle Air Controls

Volkswagen uses different types of idle air control systems. Most CIS and some early CIS-E systems use an idle boost valve and/or an auxiliary air regulator. The boost valve increases idle speed when the engine is under load at idle. Models with air conditioning will have another boost valve which is used when the air conditioning is turned on. The auxiliary air regulator is used to bypass additional air around the throttle plate to increase idle speed when the engine is cold.

Most CIS-E systems use an idle air stabilizer valve which constantly adjusts idle speed under all conditions.

Some early Volkswagen engines use an ignition advance type of idle speed control. Refer to Engine Performance And Tune-up for testing procedures of these systems.

IDLE BOOST VALVES
  1. Run the engine until normal operating temperature is reached.
  2.  
  3. Turn all electrical accessories ON, except the air conditioner (if equipped).
  4.  
  5. Lower the idle speed by turning the adjusting screw. At about 750 rpm, the boost valve should turn on and increase the idle speed.
  6.  
  7. Pinch the hose from the idle boost valve(s) shut with a clamp. The idle speed should drop.
  8.  
  9. Adjust the idle speed (with hose from the boost valve pinched shut) to 875-925 rpm.
  10.  
  11. Remove the clamp from the hose. The idle speed should increase. At about 1050 rpm, the boost valve should turn off and the idle speed should drop to specification.
  12.  

On models with air conditioning, perform these additional steps:

  1. Run the engine until normal operating temperature is reached.
  2.  
  3. Make sure all electrical accessories are OFF, including the air conditioner.
  4.  
  5. Pinch the hose from the boost valves shut with a clamp. The idle speed should not drop.
  6.  
  7. Turn the air conditioning ON, the idle speed should drop.
  8.  

AUXILIARY AIR REGULATOR
  1. The engine must be cold (coolant temperature below 86°F (30°C), and the ignition key must NOT have been in the ON position for at least an hour.
  2.  
  3. Unplug the connector from the auxiliary air regulator.
  4.  
  5. Start the engine and pinch the hose leading from the auxiliary air regulator to the intake manifold shut with a clamp. The idle speed should drop.
  6.  
  7. Engage the connector to the regulator and remove the clamp. Run the engine to normal operating temperature.
  8.  
  9. When the engine is warm, pinch the hose shut with the clamp again. This time the idle speed should not drop.
  10.  

IDLE AIR STABILIZER
  1. With the ignition ON (engine not running), you should feel the stabilizer vibrate or hum. If not, continue with the test.
  2.  
  3. The ignition switch should still be in the ON position (engine not running). Unplug the connector from the stabilizer valve.
  4.  
  5. Check the stabilizer valve with an ohmmeter. There should be continuity between the center terminal and each of the outer terminals.
  6.  
  7. Connect the positive lead of a voltmeter to the center terminal of the connector (not the valve) and the negative lead to ground. The voltmeter should display approximately 12 volts. With the positive lead still connected to the center terminal, connect the negative lead to outer terminals (one at a time). There should be 10 volts present at each of the outer terminals.
  8.  

Airflow Sensor Potentiometer

See Figure 5

The airflow sensor potentiometer sends a signal of the sensor plate position to the control unit.

  1. Remove the air intake boot.
  2.  
  3. Unplug the connector from the potentiometer.
  4.  
  5. Connect an ohmmeter to terminals 1 and 2 of the potentiometer. There should be more than 4,000 ohms present.
  6.  
  7. Connect an ohmmeter to terminals 2 and 3 of the potentiometer. There should be less than 1,000 ohms present.
  8.  



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Fig. Fig. 5: Airflow sensor potentiometer terminal identification

  1. With the ohmmeter still connected to terminals 2 and 3 of the potentiometer, slowly lift the sensor plate through its entire range of travel. The resistance should rise evenly to over 4,000 ohms.
  2.  

Differential Pressure Regulator

The control unit regulates the air/fuel ratio by adjusting the pressure in the lower chambers of the fuel distributor. The differential pressure regulator is attached to the side of the fuel distributor. It consists of a plate with an electromagnet on either side. The control unit regulates the current to the magnets, moving the plate side-to-side, which controls the size of the opening to the lower chamber. When the lower chamber pressure is high, the diaphragms are pushed up towards the outlets of the upper chamber, making the outlets smaller and reducing fuel flow. This provides for very fine adjustment of fuel flow (to the injectors) while maintaining the same pressure (at the injectors).

To test the differential pressure regulator, please refer to the fuel pressure tests in Fuel System .

 
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