Honda Accord/Prelude 1984-1995 Repair Guide

Programmed Fuel Injection (PGM-FI) System-1985-89 Models

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GENERAL INFORMATION



In order to get proper amount of fuel into the cylinders at the correct instant, the control system must perform various separate functions. The Electronic Control Unit (ECU), which is the heart of the PGM-FI system, uses an eight-bit microcomputer and consists of a Central Processing Unit (CPU), memory data, and Input/Output (I/O) ports. Basic data stored in the memory is modified by the signals sent from the various sensors to provide the correct air/fuel mixture for all engine needs.

As useful as the tests found in this section are, the first step in repair or service to engine management systems is still to gain as much information as possible about the problem; when and under what conditions it occurs. At highway speed- At idle only- Only under heavy load or hard acceleration- Wet weather- Defining the problem will eliminate many systems from consideration and possibly point to the affected system. Before diving into an extended electrical diagnosis, take the time to review the basics. Check every vacuum line for cracks or leaks. Check every electrical connector for corrosion or loose pins. Quite often, simply unplugging and reconnecting a connector will break up corrosion on the pins and restore the circuit. Watch out for poor grounds, particularly if the car has experienced major bodywork.

SERVICE PRECAUTIONS





Do not operate the fuel pump when the fuel lines and tank are empty, or when the fuel pump has been removed from the tank.
 
Do not reuse fuel hose clamps.
 
The washer(s) below any fuel system bolt (banjo fittings, service bolt, fuel filter, etc.) must be replaced whenever the bolt is loosened. Do not reuse the washers; a high-pressure fuel leak may result.
 
Make sure all ECU harness connectors are fastened securely. A poor connection can cause a high voltage surge and result in damage to integrated circuits.
 
Keep all ECU parts and harnesses dry during service. Protect the ECU and all solid-state components from rough handling or extremes of temperature.
 
Before attempting to remove any parts, turn the ignition switch OFF and disconnect the battery ground cable.
 
Always use a 12 volt battery as a power source, never a booster or high-voltage charging unit.
 
Do not disconnect the battery cables with the engine running.
 
Do not unplug any wiring connector with the engine running or the ignition ON , unless specifically instructed to do so.
 
Do not depress the accelerator pedal when starting.
 
Do not rev up the engine immediately after starting or just prior to shutdown.
 
Do not apply battery power directly to injectors.
 
Whenever possible, use a flashlight or a shatter-proof drop light. The bulbs used in standard drop lights may shatter on impact, creating a spark which may ignite fuel vapors.
 
Keep all open flame and smoking material out of the area.
 
Use a shop cloth or similar to catch fuel when opening the fuel system.
 
Relieve fuel system pressure before servicing.
 
Always use eye or full-face protection when working around fuel lines, fittings or components.
 
Always keep a dry chemical (class B-C) fire extinguisher near the area.
 

COMPONENT TESTING



Manifold Air Pressure (MAP) Sensor

See Figure 1

This sensor converts manifold air pressure readings into electrical voltage signals and sends them to the ECU. This information is used along with signals from the crank angle sensor to compute the basic injector duration.

  1. Disconnect the vacuum hose between the MAP sensor and throttle body; plug the opening in throttle body. Connect a vacuum hand pump to the open end of vacuum tube.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: A hand vacuum pump can be used to test the MAP sensor

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the wire harness from the control unit. Connect system checker harness (07999-PD6000A or equivalent) between the control unit and the wire harness connector.
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Turn the ignition switch ON . Connect a digital voltmeter positive probe to terminal C 11 of the system checker harness and the negative probe to terminal C 14. Measure the voltage between the two terminals. The voltmeter should indicate 0.5 volts at 4 in. Hg (100 mm Hg) of vacuum and 4.5 volts at 45 in. Hg (1200 mm Hg).
  8.  
  9. If the voltage is incorrect, check the vacuum hose for leakage and check the wires between the control unit and sensor for open or short circuits. Replace the sensor if wires are OK.
  10.  

Atmospheric Pressure (PA) Sensor

Like the MAP sensor, this sensor converts atmospheric pressures into voltage signals. The ECU modifies the basic injector duration to compensate for changes in the atmospheric pressure.

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the wire harness connector from the control unit. Connect system checker harness (07999-PD6000A or equivalent) between the control unit and the wire harness connector.
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Turn the ignition switch ON . Connect a digital voltmeter positive probe to terminal C 9 of system checker harness and the negative probe to terminal C 12. Measure the voltage between the two terminals. Voltmeter should indicate between 2.76-2.96 volts.
  8.  
  9. If the voltage is outside this range, check for open or short circuits between the ECU and PA sensor. Replace the PA sensor if the wires are OK.
  10.  

Idle Mixture Adjuster (IMA) Sensor

See Figure 2

This sensor is located in vacuum control box No. 1. The primary objective of this unit is to maintain the correct air/fuel ratio at idle. It is used on the 1985 Accord only.

  1. Open the No. 1 control box lid and remove the rivets attaching the IMA sensor.
  2.  



Click image to see an enlarged view

Fig. Fig. 2: The IMA sensor is secured by two rivets

  1. Unplug the IMA sensor connector.
  2.  
  3. Measure the resistance between the brown and green wire terminals of IMA sensor while turning the adjuster. Resistance should be between 0.25-6.2k ohm.
  4.  
  5. Replace the IMA sensor if resistance readings are out of range.
  6.  

Coolant Temperature (TW) Sensor

See Figure 3

This sensor is a thermistor and is used to measure differences in the coolant temperature. The basic injector duration is partially based on the signals sent from this sensor through the ECU. The resistance of the thermistor decreases with a rise in coolant temperature.

  1. Unplug the connector from the sensor, then remove the sensor from the thermostat housing.
  2.  
  3. To test the sensor, suspend it in cold water and heat the water slowly. Measure resistance between the terminals. Resistance values are as follows:

    0.98-1.34k ohms at 95°F (40°C)
     
    0.22-0.35k ohms at 176°F (80°C)
     

  4.  



Click image to see an enlarged view

Fig. Fig. 3: The coolant and air intake temperature sensors can be tested using the same procedure

  1. Replace the sensor if resistance is outside the specified range. Tighten it to 20 ft. lbs. (28 Nm).
  2.  

Intake Air Temperature (TA) Sensor

See Figure 3

This device is a thermistor and is placed in the intake manifold or air inlet boot. It acts much like the coolant temperature sensor, but has a reduced thermal capacity for quicker response.

  1. Unplug the connector from the sensor, then remove the sensor from the intake manifold or air inlet boot.
  2.  
  3. To test the sensor, suspend it in cold water and heat the water slowly. Measure resistance between the terminals. Resistance values are as follows:

    1985 Accord-0.98-1.34k ohms at 95°F (40°C)
     
    1985 Accord-0.22-0.35k ohms at 176°F (80°C)
     
    1986-89 Accord and Prelude-0.98-1.34k ohms at 104°F (40°C)
     
    1986-89 Accord and Prelude-0.22-0.35k ohm at 176°F (80°C)
     

  4.  
  5. Replace the sensor if resistance is outside the specified range.
  6.  

Cylinder (CYL) Sensor

The CYL sensor is used to detect the position of No. 1 cylinder; the signal is used to trigger the sequential fuel injection.

1985-89 ACCORD AND 1985-87 PRELUDE
  1. Unplug the connector of the crank angle/cylinder sensors on the distributor.
  2.  
  3. Measure resistance between the orange and white terminals of the sensor. Resistance should be 650-850 ohms.
  4.  
  5. Measure the resistance between both terminals of the sensor and crank angle sensor housing. Resistance should 100k (100,000) ohms or more.
  6.  

1988-89 PRELUDE
  1. Unplug the connector from the cylinder sensor (next to the distributor).
  2.  
  3. Measure the resistance between the two terminals of the sensor. Resistance should be between 700-1000 ohms.
  4.  
  5. Check for continuity between the two sensor terminals and ground. If continuity exists, replace the sensor.
  6.  

Crank Angle (TDC/CRANK) Sensors

The CRANK or crankshaft angle sensor signal is used to determine the fuel injection and ignition timing. It is also used to generate the engine speed signal. The TDC sensor signal is used to determine ignition timing during start-up or when the CRANK signal is abnormal. The TDC and CRANK sensors are incorporated in one unit.

1985-89 ACCORD AND 1985-87 PRELUDE
  1. Unplug the connector of the crank angle/cylinder sensors on the distributor.
  2.  
  3. Measure resistance between the orange/blue and white/blue terminals of the sensor. Resistance should be 650-850 ohms.
  4.  
  5. Measure the resistance between both terminals of the sensor and crank angle sensor housing. Resistance should 100k (100,000) ohms or more.
  6.  

1988-1989 PRELUDE
  1. Unplug the connector of the crank angle sensor on the distributor.
  2.  
  3. Measure resistance between the two top terminals of the sensor connector (located under the locking tab). Resistance should be 700-1000 ohms.
  4.  
  5. Check for continuity between both of the top two terminals of the sensor and ground. If continuity exists, replace the sensor.
  6.  

Throttle Angle Sensor

This sensor is a potentiometer which translates the position of the throttle plate to an electrical signal. The signal is near 0 volts at idle and increases to just under 5 volts at wide open throttle. The sensor is mounted to the side of the throttle body.

Do not adjust throttle valve stop screw; it is preset at factory.

  1. Unplug the connector of the throttle angle sensor.
  2.  
  3. On 1985 Accords, measure the resistance between the yellow and green wire terminals at the sensor. Resistance should be between 3.2-7.2k (3200-7200) ohms.
  4.  
  5. On 1986-89 Accords and Preludes, measure the resistance between the yellow/white and green/white wire terminals at sensor. Resistance should be between 4-6k (4000-6000) ohms.
  6.  
  7. If the resistance is not as specified, replace the sensor.
  8.  

 
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