BMW Coupes and Sedans 1970-1988 Repair Guide

Injection Valves

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See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Cut-away view of an injection valve

The injection valves must open at a minimum fuel pressure of 47 psi (320 kPa).

TESTING



  1. Connect a pressure valve and shut-off valve in the pressure line to the fuel distributor, with the pressure gauge on the fuel distributor side of the shut-off valve.
  2.  
  3. Open the shut-off valve, remove the injectors from the intake manifold and turn the ignition switch ON .
  4.  
  5. Disconnect the terminal plug from the mixture control unit.
  6.  
  7. Lift the sensor plate for a maximum of 4 seconds.
  8.  
  9. The pressure should not drop more than 4 psi (27 kPa). If the pressure drops more than the specifications, the fuel filter is clogged, fuel pump rate is inadequate or the fuel tank is empty.
  10.  

REMOVAL & INSTALLATION



  1. Remove the rubber intake hose leading from the mixture control unit to the throttle unit. Remove the 4 retaining nuts for each, and then remove No. 2 and No. 3 intake pipes.
  2.  
  3. The injector valves incorporate union nuts and flatted section on each valve to permit the lines to be attached to the valves. However, the injection lines need not be disconnected to remove the valves, which are simply pressed into the intake ports.
  4.  
  5. To remove each valve, simply pass a small prytool downward between the intake header and the cam cover, insert the blade into the groove between the fuel line nut and flatted portion of the injection valve, and pry out. After the valve is out of the port, hold the flatted section of the valve with a wrench, use another wrench to unscrew the union nut, and disconnect the fuel line.
  6.  

To install:
  1. Press the white insulating bushing back into the intake port, if it came out with the valve. Then, press the rubber seal into the grove. Finally, snugly press in the injection valve. Reinstall the intake pipes, using new gaskets.
  2.  

INJECTION VALVE COMPARISON



If the compression and air induction systems are normal, but the engine is operating erratically, the injector valves should be tested with the use of a special tool (13 5 030) or equivalent.

Testing

See Figure 2

  1. The tool consists of scaled measuring tubes. Insert each injector valve into one of the tubes and secure. Disconnect the wire terminal plug from the mixture control valve, turn the ignition switch ON . Lift the sensor plate so that the injectors will fill the tubes with fuel.
  2.  
  3. Empty the tubes and again fill the tubes with fuel until the 15cc mark is reached on one tube. Compare the difference between the tubes for the fuel levels. The difference should not be over 15%.
  4.  
  5. If the fuel level difference is over 15% between tubes, exchange a good injector valve with a questionable one and repeat the test.
  6.  
  7. If the questionable injector valve flow rate remains the same, the valve is defective and must be replaced. If the injector valve flow rate is normal, the fuel distributor unit is defective and must be replaced.
  8.  
  9. Also check the spray pattern of each injector. Refer to the injector spray pattern chart, and compare to the actual spray pattern of the injector.
  10.  



Click image to see an enlarged view

Fig. Fig. 2: Injector spray pattern chart

 
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