Initial Inspection
1.8 LITER L-JETRONIC SYSTEM
The system adapted for the 4-cylinder 1.8 liter engine represents the third generation of L-Jetronic development. The major changes are as follows.
1. The control unit is smaller and lighter. Integrated circuits (IC's) are used to replace many electrical components. The combined relay is deleted as is the injector current control system. This allows for a reduction in plug size down to 25 pins.
2. The injectors have high resistance brass windings which act like line resistors. The final stage in the control unit is current switched rather than current controlled. The injectors are wired in parallel to pin number 12 in the E.C.U. plug.
3. Air Flow Meter design has been optimized with mechanical improvements and electrical modifications. A fuel pump switch is no longer incorporated since the pump is controlled by a pump relay (which is monitoring the ignition system). The air temperature sensor signal is combined with the potentiometer signal thus reducing the number of wires from the A.F.M. to the E.C.U.
4. System pressure is 3.0 bar (with the vacuum line disconnected).
IDLE SPEED CONTROL SYSTEM
An electronically governed idle rpm control valve keeps the idle speed stable under the various engine operating conditions. Measured intake air from the air flow meter bypasses the throttle plate through the idle rpm control valve and subsequently calls for additional fuel injection. The amount of bypass air is determined by the variable orifice of the valve.
The valve is current controlled. It is closed with 500 mA and full open at 0 Amp. While cranking the valve is full open.
An additional electronic control unit, the Idle Speed CU, controls the orifice opening according to the engine speed and the engine operating conditions as related to engine coolant temperature, transmission, air conditioning, and ambient air temperature.
IDLE CONTROL SPEEDS
Automatic transmission
1. In drive, 1 or 2 = 750 rpm
2. Park or Neutral
a) engine cold < 45°C
b) engine warm > 45°C = 950 rpm
i) ambient air temp < 0°C = 850 rpm
ii) ambient air temp > 0°C
-A/C on = 850 rpm
-A/C off = 750 rpm
Manual Transmission
1. Engine cold < 45°C = 950 rpm
2. Engine warm > 45°C
a) ambient air temp < 0°C = 850 rpm
b) ambient air temp > 0°C
-A/C on = 850 rpm
-A/C off = 750 rpm
Modification
To avoid gear noise and rough idle, the 0°C switch is jumpered and a diode harness fitted. On the automatic transmission cars to avoid NC and idle control unit problems, the diode harness is also fitted.
These changes were incorporated into production in mid 1984.
FUEL SHUT-OFF
An adaptive fuel shut-off system is incorporated into the fuel injection system. The speed at which injection is resumed after deceleration shut-off depends on both engine temperature and decelation rate.
On a warm engine the cut-in speed will be between 1400 and 900 rpm depending on deceleration rate. A higher cut-in speed is obtained with a higher deceleration rate.
At engine temperatures below 176°F the cut-in speeds will be increased by up to an additional 300 rpm.
Note: To prevent stalling. the deceleration fuel shutoff feature does not operate when the air conditioning compressor is engaged.
If the vehicle is accelerating with a closed throttle switch i.e. rolling downhill, the injection will shut off between 2800 and 4000 rpm. depending on temperature and E.C.U. tolerance.
Injection also shuts off above 6200 rpm to limit engine speed.
MIXTURE ADJUSTMENTS
The injection control unit with lambda controls designed to maintain the mixture at an air/fuel ratio of approximately Lambda=1. When the mixture is correct the output voltage of the integrator stage is Battery voltage x 1/2 - 300 mV. When the mixture is too lean this integrated voltage is higher and when the mixture is too rich the voltage is lower.
The fact that integrator voltage is proportional to actual mixture levels allows for an electronic means of measuring and resetting the mixture and consequently the exhaust emission values.
A Digital Mixture Measurement Unit #88 88 6 126 400 issued for this purpose. The unit plugs into the 15 pin diagnostic connector and should be used in conjunction with the BMW Service Tester.
PRESSURE SENSOR
A pressure sensor is mounted to the outside of the air cleaner on automatic transmission cars only. This allows these vehicles to meet emission requirements at higher elevations. The sensor is wired to pin #11 on the electronic control unit and acts to lean off the mixture.
DIGITAL MIXTURE MEASUREMENT UNIT
Instructions for Checking/Adjusting Integrator Voltage
1. Testing Requirements:
- Engine at operating temperature, i.e. oil temperature at least 60°C.
- Ignition timing and valve clearance is correct.
- Idle speed (control) is correct.
- Electrical consumers, i.e. air conditioner, etc., switched off.
2. Connect DIGITAL MIXTURE MEASUREMENT UNIT on diagnosis socket. (BMW SERVICE TEST Unit or BMW [Siemens] Tester can also be connected on diagnosis Socket.)
3. Check engine idle speed.
4. Function display must flash uniformly (at least once every 3 seconds, to indicate that the oxygen sensor control system is operating properly).
5. Disconnect oxygen sensor plug in engine compartment. (Green oxygen sensor wire should not be grounded, i.e. shorted against the manifold, etc.)
6. Disconnect charcoal cannister purge line (at the throttle housing).
Do not plug openings.
7. Read "required voltage on DIGITAL MIXTURE MEASUREMENT UNIT and note value (e.g. 6.7V).
8. Connect oxygen sensor plug.
9. Read the integrator voltage on LCD display while LED is flashing (correct measured value can be read only after waiting 10 to 15 seconds).
10. Adjust integrator voltage to noted nominal value +/- 0.2 volts.
Note: It LED is not flashing, do not adjust integrator voltage Check oxygen sensor for proper operation.
11. Adjusting Integrator Voltage:
- Drill out anti-tamper plug with Special Tool 13 1 092.
- Screw Special Tool 13 1 094 into the anti-tamper plug and pull the anti-tamper plug out of the air flow sensor.
- Adjust integrator voltage to nominal value by turning control Screw with Special Tool 13 1 060 (or 5mm allen head screw if equipped)
- Install new anti-tamper plug after finishing adjustments
12. Connect charcoal cannister purge line.
VACUUM ADVANCE CONTROL SYSTEM
The distributor vacuum advance unit is connected by a hose to a fitting on the throttle valve. The vacuum signal is controlled by an electromagnetic valve mounted on the firewall. A relay controls the ground for the valve which is powered closed.
The relay is wired to a 113°F temperature switch (which is combined with the temperature gauge sensor), an intake air temperature sensor (with two sensing points: 50°F and 100°F) and the fuel injection control unit (for load sensing).
The relay logic circuits control vacuum advance as follows:
1. Intake air temperature < 50°F - vacuum advance to aid starting
2. Intake air temperature > 50°F - no advance for faster
Coolant temperature < 113°F - warm up
3. Intake air temperature > 50°F - vacuum advance
Coolant temperature > 113°F
4. Intake air temperature high engine load > 100°F - no advance to avoid pinging
In order to properly test the vacuum advance control relay the various temperature and load signals must be simulated. For this purpose a special tool has been developed and should be used while performing Engine Test 06 on the BMW Service Tester.
Checking Operation of Vacuum Advance Control System
- Pull off relay 3 and plug it on VACUUM ADVANCE CONTROL SIMULATOR.
- Connect plug 4 - see picture.
- Connect BMW SERVICE TEST Unit.
- Start engine and run at idle speed.
- The ignition timing displayed will already be "retarded" about 20 degrees on crankshaft by the simulator when switch 1 is positioned at "a".
- Lamp MV comes on to indicate that the solenoid is activated; the hose to the vacuum box is vented to atmosphere through the solenoid. This indicates no vacuum advance.
- Lamp tp (load signal) will flash during the entire test.
- Check the following points-see instructions on simulator.
1. Switch 1 set to "a"-lamp MV on (no advance). Switch 2 switched over to other position -ignition timing should not change.
2. Switch 1 set to "b"-lamp MV goes out. Ignition timing "advanced" about 20 degrees on crankshaft. Switch 2 switched over to other position - no ignition timing change.
3. Switch 1 set to "c"-same reading as "b" above.
4. Switch 1 set to "d" and switch 2 to 0 -lamp MV goes out, vacuum on advance box- ignition timing "advanced" about 20 degrees, switch 2 position 1 - lamp MV on (no advance)
Checking Coolant and intake Air Temperature Sensors
In this test the function of temperature switches and corresponding wires is checked. The values can be checked in the plug jacks with an ohmmeter.
The following values should be reached.
Sensor for
- air temperature > 10°C... < 38°C approx. 950 ohms
- coolant temperature opens at < 45°C infinite ohms closes at > 45°C 0 ohms (see NOTE)
NOTE: If the COOLANT temperature switch is checked with coolant temperature < 45°C the plug on the idle speed control unit (in glove box above L-Jetronic control unit) must be disconnected.
Troubleshooting -VACUUM ADVANCE CONTROL SIMULATOR connected-
Lamp "tp" (Load signal) not flashing
- No Load signal
- No power supply on simulator
- LJetronic control unit, connections or wire harness defective
- Engine running erratically or not at all
Lamp "MV" not on
- No power Supply on simulator
- Wire harness for simulator defective
- Vacuum advance control unit detective
No advance control
- Vacuum advance control unit defective
- Connections or wire harness for solenoid defective
Ignition timing not reached
- Solenoid defective
- Vacuum hose leaks
- Distributor defective
- Vacuum advance control unit defective
ENGINE CHANGES
1. The cooling capacity and flow rate have been increased and an 8 blade visco fan provides temperature controlled ventilation.
2. The compression ratio is 9.3:1 to improve fuel economy efficiency.
3. The intake and exhaust manifolds are engineered for increased engine torque and good emission control.