Dodge Omni/Horizon/Rampage 1978-1989 Repair Guide

Electronic Feedback Carburetor (EFC) System

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GENERAL INFORMATION



The EFC system is essentially an emissions control system which utilizes an electronic signal, generated by an exhaust gas oxygen sensor, to precisely control the air-fuel mixture ratio in the carburetor. This allows the engine to produce exhaust gases of the proper composition to permit the use of a three-way catalyst. The three-way catalyst is designed to convert the three pollutants (1) Hydrocarbons (HC), (2) Carbon Monoxide (CO), and (3) Oxides of Nitrogen (NO x ) into harmless substances.

There are two operating modes in the EFC system:



Open Loop-Air fuel ratio is controlled by information programmed into the computer at manufacture.
 
Closed Loop-Air fuel ratio is varied by the computer based on information supplied by the oxygen sensor.
 

When the engine is cold, the system will be operating in the open loop mode. During that time, the air fuel ratio will be fixed at a richer level. This will allow proper engine warm-up. Also during this period, air injection (from the air injection pump) will be injected upstream in the exhaust manifold.

The computer has been programmed to monitor various component systems. If a malfunction of a system occurs, a fault code will be stored in the computer. If the problem is repaired or corrects itself, the computer will erase the code after thirty ignition cycles.

READING CODES



In order to read the computer and find the fault code, diagnostic readout tool C-4805 or equivalent will be needed. If a fault code appears on the read-out tool, perform a careful visual check of all vacuum lines and electrical connections before doing any repairs to the system. The diagnostic read-out tool can be used to check out three different problem modes. They are the diagnostic test mode, circuit actuation test mode and switch test mode. The diagnostic test mode is used to retrieve fault codes that are stored in the computer. The circuit actuation test mode is used to analyze various systems. The switch test mode is used to test various switch circuits.

Diagnostic Mode
  1. Install the readout tool to the wiring connector which is located on the left shock tower.
  2.  
  3. Position the read/hold switch on the tool to the read position.
  4.  
  5. Open the carburetor switch by placing the fast idle screw on the highest step of the fast idle cam.
  6.  
  7. Position the ignition switch in the RUN position and wait for fault code 00 to appear on the tool display screen.
  8.  
  9. Move the read/switch to the hold position.
  10.  
  11. Record all fault codes that may appear. The display fault codes may be stopped by switching the tool to the read position. Fault codes will continue when the tool is switched back to the hold position.

    CODE 00-indicates that the diagnostic readout tool is functioning and receiving power
     
    CODE 11-indicates that a problem exists in the oxygen solenoid control circuit
     
    CODE 12-indicates a problem in the transmission unlock relay
     
    CODE 13-indicates that a problem exists in the canister purge solenoid circuit
     
    CODE 14-indicates that the vehicle battery has been disconnected
     
    CODE 16-indicates that there is a problem in the radiator fan control circuit in vehicles equipped with the 2.2L engines. If vehicle is equipped with air condition disregard this fault code
     
    CODE 17-indicates that a problem exists in the electronic throttle control vacuum solenoid system on vehicles equipped with a 2.2L engine
     
    CODE 18-indicates a problem in the vacuum operated secondary control solenoid system on vehicles equipped with the 2.2L engine
     
    CODE 21-indicates a problem in the distributor pick up system
     
    CODE 22-indicates that the oxygen system is stuck in full lean position
     
    CODE 23-indicates that the oxygen sensor is stuck in the full rich position
     
    CODE 24-indicates a problem in the computer
     
    CODE 25-indicates a problem in the radiator fan coolant sensor portion of the engine temperature dual sensor system on vehicles equipped with the 2.2L engine
     
    CODE 26-indicates a problem in the engine temperature portion of the engine temperature dual sensor system
     
    CODE 28-indicates a problem in the distance sensor system on vehicles equipped with manual transmission
     
    CODE 31-indicates that the engine has not been cranked since the battery was disconnected
     
    CODE 32-indicates a problem in the computer
     
    CODE 33-indicates a problem in the computer
     
    CODE 55-indicates the end of a message
     
    CODE 88-indicates the end of a message
     

  12.  

Circuit Actuation Testing
  1. Put the system into diagnostic mode testing and wait for code 55 to appear on the tool test screen.
  2.  
  3. Press the ATM function button on the tool to activate the display. If a specific ATM test is desired, hold the button down until the proper test code appears.
  4.  
  5. The computer will continue to turn the selected circuit on and off for as long as five minutes or until the ATM button is pressed again or if the ignition switch is turned OFF .
  6.  
  7. If the ATM button is not pressed again, the computer will continue cycling the selected circuit for five minutes and then shut the system off. Turning the ignition switch OFF will also shut the test mode off. Code description is as follows:

    CODE 91-oxygen feedback solenoid activated
     
    CODE 92-shift indicator light on the instrument panel activated (manual transmission)
     
    CODE 93-vacuum operated secondary solenoid activated
     
    CODE 96-fan relay activated
     
    CODE 97-electronic throttle control solenoid activated
     
    CODE 98-canister purge solenoid is activated
     

  8.  

Switch Testing Mode
  1. Put the system into diagnostic mode testing and wait for code 55 to appear on the test screen.
  2.  
  3. Check that both air conditioning and heated rear window switches are in the off position.
  4.  
  5. Press the ATM button on the tool and immediately move the read/hold switch to the read position.
  6.  
  7. Wait for code 00 to appear on the test screen.
  8.  
  9. Turn the air conditioning switch to the on position. If the computer is receiving input, the display will change to 88 when the switch is turned on and switch back to 00 when the switch is turned off. Repeat the test for the heated rear window switch.Code description is as follows:

    CODE-00 air conditioning and heated rear window switches are off
     
    CODE-88 air conditioning or heated rear window switches are on
     

  10.  

CLEARING CODES



The computer will automatically erase the code(s) thirty ignition cycles after the problem has been repaired. The code(s) may also be erased manually by disconnecting the negative battery cable for 30 seconds.

 
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