Chrysler RAM50/D50/Arrow 1979-1993 Repair Guide

Multi-port Fuel Injection Relay

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OPERATION



See Figures 1 and 2

While the ignition switch is ON, battery power is supplied to the engine control module, injectors, volume air-flow sensor, etc. Turning the ignition switch to the ON position causes current to flow from the ignition switch through the MFI relay coil to ground. This turns the MFI relay switch on and supplies power from the battery to the engine control module via the MFI relay switch.



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Fig. Fig. 1: Location of the Multi-port Fuel Injection (MFI) relay on 2.4L equipped vehicles



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Fig. Fig. 2: Location of the Multi-port Fuel Injection (MFI) relay on 3.0L equipped vehicles

HARNESS TESTING



2.4L Engines

See Figure 3

The 1993, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. With the MFI relay harness unplugged from the relay and the ignition switch ON, measure the power supply voltage to terminal 8 of the harness connector. If there is no voltage present, the problem lies in the ignition switch or in the harness between the ignition switch and the MFI relay connector, these should be repaired or replaced as needed.
  2.  
  3. Check for continuity of the ground circuit on terminal 6 of the MFI relay harness connector. The ignition should be OFF and the MFI relay still unplugged. If continuity is present, stop the check, the problem lies elsewhere. If there is no continuity, repair or replace the harness between the MFI relay and ground.
  4.  
  5. With the MFI connector still unplugged, measure the power supply voltage of terminal 4 of the MFI relay. If the power is not sufficient (the power is the voltage of the battery, therefore around 10-12 volts), repair the harness between terminal 4 and the battery.
  6.  
  7. Disconnect the Engine Control Module (ECM) connector, and the MFI relay connector should still be unplugged. Check for an open-circuit, or short-circuit to ground, between the ECM (terminals 102 and 107) and the MFI relay (terminal 3). If an open-circuit is found, repair the harness between the ECM and terminal 3 of the MFI relay. If no short-circuit is found, the component is OK.
  8.  



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Fig. Fig. 3: The MFI harness connector and terminal identification-2.4L engines

3.0L Engines See Figure 4

When performing these checks, use a harness side connector to fasten onto the different terminals.

  1. Disconnect the ECM harness. Measure the ignition switch-IG terminal (terminal 110) input voltage. With the ignition switch OFF, the voltage should be 0-1 volts. When the ignition switch is ON, the voltage should be that of the battery (around 10-12 volts). If the circuit shows these voltages, go on to Step 2, otherwise repair the harness between terminal 110 and the ignition switch.
  2.  



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Fig. Fig. 4: The numbered terminal locations on the MFI harness connector-3.0L engines

  1. Turn the ignition switch OFF and unplug the MFI relay connector. Measure the power supply voltage of the MFI relay (terminal 10 to ground). If the voltage is that of the battery, continue on to Step 3, otherwise repair the harness between terminal 10 and the battery.
  2.  
  3. With both the ECM and the MFI relay connectors unplugged, check for an open-circuit or a short-circuit to ground between the MFI relay (terminal 8) and the ECM (terminals 66 and 63). If no short-circuit is found, move on to Step 4, otherwise repair the harnesses between terminal 8 and terminals 66 and 63.
  4.  
  5. Keep both the ECM and the MFI relay connectors unplugged and check for an open-circuit between terminal 4 of the MFI and terminals 102 and 107 of the ECM. If a short-circuit is found, repair the harnesses between the terminals, otherwise go on to Step 5.
  6.  
  7. Connect the ECM and the MFI relay. While cranking the engine to start it, measure the power supply voltage of the actuator (terminal 5 of the MFI to ground). The voltage should be 8 volts or higher. Once the engine is running, race the engine and measure the voltage again. The voltage should be at the battery level. If the voltage is not as indicated, either the ECM or the MFI relay is defective.
  8.  

COMPONENT INSPECTION



2.4L Engines

See Figure 5

The 1993, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. Remove the MFI relay.
  2.  
  3. Check the continuity between the MFI relay terminals. Check terminals 3-5 and 2-5, which should register approximately 95 ohms. Check terminals 6-7, which should register 35 ohms. Check terminals 6-8, which will only be connected one way.
  4.  
  5. By using the jumper wire, connect terminal 7 of the MFI relay to the (+) terminal of the battery and terminal 6 to the (-) terminal of the battery.
  6.  


WARNING
If the jumper leads are not connected to the proper terminals, the relay will be damaged.

  1. While connecting the jumper wire on the (-) side of the battery, check continuity between the terminals 1 and 4 of the MFI relay. While connected, the resistance should be 0 ohms, and infinite resistance when disconnected.
  2.  
  3. By using the jumper wire, connect terminal 2 of the MFI relay to the (+) terminal of the battery and terminal 5 to the (-) terminal of the battery.
  4.  
  5. While connecting the jumper wire on the (-) side of the battery, check continuity between the terminals 1 and 4 of the MFI relay. While connected, the resistance should be 0 ohms, and infinite resistance when disconnected.
  6.  
  7. By using the jumper wire, connect terminal 8 of the MFI relay to the (+) terminal of the battery and terminal 6 to the (-) terminal of the battery.
  8.  
  9. While connecting the jumper wire on the (-) side of the battery, check continuity between the terminals 2 and 4 of the MFI relay. While connected, the resistance should be 0 ohms, and infinite resistance when disconnected.
  10.  
  11. Replace the MFI relay with a new one, if a malfunction occurred with the tests.
  12.  



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Fig. Fig. 5: Testing connections for the MFI relay--if the relay does not pass all of the tests, it needs to be replaced with a new unit

3.0L Engines See Figure 6

  1. Remove the MFI relay.
  2.  
  3. By using the jumper wire, connect terminal 10 of the MFI relay to the (+) terminal of the battery and terminal 8 to the (-) terminal of the battery.
  4.  



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Fig. Fig. 6: Testing connections for the MFI relay-if the relay does not pass all of the tests, it needs to be replaced with a new unit.


WARNING
If the jumper leads are not connected to the proper terminals, the relay will be damaged.

  1. While connecting the jumper wire on the (-) side of the battery, check the voltage at terminals 4 and 5 of the MFI relay. While connected, the voltage should be the battery voltage, and the voltage should be 0 volts when disconnected.
  2.  
  3. By using the jumper wire, connect terminal 9 of the MFI relay to the (+) terminal of the battery and terminal 6 to the (-) terminal of the battery.
  4.  
  5. While connecting the jumper wire on the (-) side of the battery, check continuity between the terminals 2 and 3 of the MFI relay. While connected the continuity should be 0 ohms, and the continuity should be infinite ohms when disconnected.
  6.  
  7. By using the jumper wire, connect terminal 3 of the MFI relay to the (+) terminal of the battery and terminal 7 to the (-) terminal of the battery.
  8.  
  9. While connecting the jumper wire on the (-) side of the battery, check the voltage between at terminal 2 of the MFI relay. While connected the voltage should be the battery voltage, and the voltage should be 0 volts when disconnected.
  10.  
  11. Replace the MFI relay with a new one, if a malfunction occurred with the tests.
  12.  

REMOVAL & INSTALLATION



The MFI relay is located on the right-hand side kick-panel, or up under the dashboard. It is the uppermost of the two relays located there. It is mounted to the kick-panel with two screws and has one 8-terminal (for 2.4L engine) or a 10-terminal (for 3.0L engines) connector plugged into it. Remove, the screws and unplug the connector to remove.

 
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