Testing On/Off Ratio (Air Fuel Ratio)

Testing on/off ratio

Idle Speed, Lambda Control:

TSZ Ignition Point:

Special Tools:

Commercially Available Testers:

Shop-made tool



Drift for inserting steel anti-tamper lock




Note:
The adjustment device (2) for the fuel/air mixture setting is secured with a steel anti-tamper lock (1) to prevent any unauthorized alteration of the setting.

This anti-tamper lock is factory-installed with a special tool after the fuel/air mixture is set and must not be removed in the workshops.

The fuel/air mixture setting may only be corrected when replacing a component of the injection system (e.g. fuel distributor) or when performing engine repairs.

In such cases, the adjustment device (2) must be replaced.

The lambda control must not be tested when the engine is very hot, e.g. immediately after a long drive or after measuring engine output on the dynamometer.


Test Procedures

1 Switch off air conditioning. Move selector lever into park position "P".




2 Connect testers:
Oil remote thermometer (018) 124 589 07 21 00
Lambda control tester (012)
Twin socket (031)
Engine tester (026)
Trigger clamp (011)

3 Position extraction device (014) at exhaust pipe.

4 Check throttle control for ease of movement and condition.

5 Test ignition point (see table).

6 Run engine to warm up oil to 80°C.

7 Test idle speed (see table).

Note: If idle speed varies, test electronic idle speed control. Testing and Inspection

8 Test lambda control (see table).

Note: The readout must fluctuate during the measurement. If a constant readout is indicated, there is a fault in the lambda control, e.g. oxygen sensor faulty. See "Testing electrical components of CFI system" for trouble diagnosis table. Testing Electrical Components of CFI System




Voltage measurement with multimeter or lambda control tester (12 volt position) at contact 3 of diagnostic connector to ground.

Test value: 2.1-4.8 volts




Switch off all ancillary components. Detach heated oxygen sensor signal plug connection (G3/2x2). Take reading of control value (e.g. 3.3 volts). Readout must not fluctuate.

Plug together heated oxygen sensor signal plug connection (G3/2x2) - readout fluctuates. Test value must vary not more than ±0.8 volts from control value. Variation >0.8 volts, set control value.




9 Adjust lambda control.

Should it be necessary to set the on/off ratio after performing engine repairs or replacing a part of the CFI system, proceed as follows:

Remove air cleaner.

Strike shear-off screws (arrow) in the middle with a chisel and drill approx. 6 - 8 mm deep with a 2.5 mm twist drill.

Caution! Do not drill through screws as the metal chips may cause engine damage. Thoroughly remove metal chips with a cloth.

Unscrew shear-off screws with left-hand drill.

Install new repair kit, Part No.102 070 01 74. Tighten screws until head shears off.

Install air cleaner.

Start engine.




Push the screwdriver (1) through the recess in the top of the air cleaner onto the adjusting device (2).

Press the adjusting device down with the screwdriver against the spring force, turn it slightly until the hexagon head (3) engages in the mixture regulating screw (61).

Turning to the left = leaner - on/off ratio or voltage rises
Turning to the right = richer - on/off ratio or voltage drops

After each adjustment, briefly blip throttle and test lambda control; reset if necessary.




Switch off engine.

Take off air cleaner.

Knock in steel anti-tamper lock (1) with shop- made drift at the chamfered side far enough for the surface of the anti-tamper lock to be flush with, or slightly lower than, the bottom edge of the taper of the adjusting device (2).

Install air cleaner.

Check smooth engine running by moving selector lever into Drive mode, switching on air conditioning/automatic climate control, turning power steering to full lock. The engine must continue to run smoothly. Test electronic idle speed control, if necessary. Testing and Inspection