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Circuit Test A1

Fig 1: TFI Module Circuits (Part 1 of 4)
G108538
Fig 2: TFI Module Circuits (Part 2 of 4)
G108539
Fig 3: TFI Module Circuits (Part 3 of 4)
G108540
Fig 4: TFI Module Circuits (Part 4 of 4)
G108541

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: fuel quantity and quality, ignition system damage, cracks, moisture, etc., engine mechanical conditions such as bad valves, timing belt, etc. Also included are starter and battery circuit problems.

  1. Starting System. Try to start engine. If engine does not crank, check vehicle starting and charging systems. Ensure fuel pump inertia switch is set (button pushed in). If engine cranks, but does not start or stalls after starting, go to next step.
  2. Checking VREF Signal at TPS. Turn key off and wait 10 seconds. Set DVOM on 20-volt scale and disconnect Throttle Position Sensor (TPS). Turn key on, leaving engine off (KOEO). Measure voltage at TPS harness connector between (VREF) and SIGNAL RETURN. If reading is less than 4 volts or more than 6 volts, go to CIRCUIT TEST A3 , step 1). If reading is between 4 and 6 volts, reconnect TPS and go to next step.
  3. Checking For Spark At Plugs. Disconnect any spark plug wire and connect spark tester between plug wire and engine ground. Crank engine and check for spark. If spark exists, connect spark plug wire and go to step 12). If there is no spark, connect spark plug wire and go to next step or to step 5) for vehicles equipped with DIS.
  4. Checking For Spark at Coil. Remove high tension coil wire from distributor and install spark tester. Check for spark while cranking engine. If spark exists, connect coil wire and service or repair TFI ignition system. If no spark exists, connect coil wire and go to next step.
  5. Ignition Ground Continuity. Turn key off and wait 10 seconds. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale and disconnect TFI or DIS (pins No. 7-12). Disconnect Hall sensor on 3.8L. Measure resistance between test pin No. 16 and TFI harness connector ignition ground. If reading is more than 5 ohms, repair harness and repeat QUICK TEST. If reading is less than 5 ohms, go to next step.
  6. Isolating SPOUT Circuit Fault. Install breakout box. Connect TFI or DIS (pins No. 7-12). For 3.8L AXOD and 3.8L RWD, connect distributor hall connector. Connect ECA to breakout box. Set breakout box switch to "DISTRIBUTOR" position. Try to start vehicle. If vehicle starts, go to step 10). If vehicle does not start, go to next step.
  7. Checking SPOUT Signal. With KOEO, connect breakout box and ECA. Move breakout box timing switch to "COMPUTED" position. Set DVOM on 20-volt scale and measure voltage between test pin No. 36 and chassis ground while cranking engine. If voltage is between 3 and 6 volts, EEC system is NOT at fault. TFI ignition system should be diagnosed. If voltage is less than 3 volts or more than 6 volts, go to next step.
  8. Checking SPOUT and PIP For Shorts. Turn key off and wait 10 seconds. With breakout box installed, disconnect ECA. On 3.8L SC, disconnect PIP sensor. Disconnect TFI. On 3.8L AXOD and 3.8L RWD, disconnect TFI and distributor Hall connector. Set DVOM on 200K-ohm scale. On SPOUT circuit, measure resistance between test pin No. 36 (SPOUT) and test pins No. 16, 20, 40, 46, and 60 for short to ground. Measure resistance between test pin No. 36 and test pins No. 26, 37 and 57 for short to power. Measure resistance between test pins No. 36 and 56 for short to PIP. On PIP circuit, measure resistance between test pin No. 56 and test pins No. 16, 20, 40, 46, and 60 for short to ground. Measure resistance between test pin No. 56 and test pins No. 26, 37 and 57 for short to power. Measure resistance between test pins No. 56 and 36 for short to SPOUT. If any reading is less than 10K ohms, repair short in harness and repeat QUICK TEST. If engine still does not start, go to next step. If all readings are 10K ohms or more, go to next step.
  9. Isolating Shorts In Processor. Turn key off and wait 10 seconds. With breakout box installed, connect ECA, but leave TFI or DIS disconnected. On 3.8L models, disconnect TFI and distributor Hall connector. Set DVOM on 200K ohm scale. On SPOUT circuit, measure resistance between test pin No. 36 (SPOUT) and test pins No. 37 and 57 for short to power. Measure resistance between test pin No. 36 and test pins No. 40 and 60 for short to ground. On PIP circuit, measure resistance between test pin No. 56 (PIP) and test pins No. 37 and 57 for short to power. Measure resistance between test pin No. 56 and test pins No. 40 and 60 for short to ground. If any reading is less than 500 ohms, replace ECA and repeat QUICK TEST. If all readings are greater than 500 ohms, connect TFI and go to next step.
  10. Checking PIP Signal. With key off, install breakout box. Set DVOM on 20-volt scale. Measure voltage between test pins No. 56 and 16, while cranking engine. If reading is between 3 and 7 volts, remove breakout box. Replace ECA and repeat QUICK TEST. If reading is less than 3 volts or more than 7 volts, go to next step.
  11. Continuity of PIP Circuit. Install breakout box, turn key off and wait 10 seconds. Set DVOM on 200-ohm scale. Disconnect ECA and TFI. Disconnect PIP sensor. Disconnect distributor Hall sensor. Measure resistance between test pin No. 56 and TFI connector PIP circuit. If reading is 5 ohms or more, repair open PIP circuit and repeat QUICK TEST. If readings is less than 5 ohms, go to next step.
  12. Verifying SPOUT Signal. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector and inspect for damaged pins, corrosion, or loose wires. Repair as necessary. Install breakout box and connect ECA. Ensure breakout box timing switch is in "COMPUTED" position. Set DVOM on 20-volt scale and measure voltage between test pin No. 36 and test pins No. 40 and 60 while cranking engine. If reading is between 3 and 6 volts, go to step 13). If reading is less than 3 volts or more than 6 volts, go to step 8).
    CAUTION: Use safety precautions when working on fuel system. No smoking or open flame. If fuel starts leaking, immediately turn key off.
  13. Fuel Pump Check. Connect pressure gauge to vehicle. Note initial pressure reading. Pressurize fuel system by turning key on for one second and observe pressure gauge. Turn key off, and wait 10 seconds. Repeat sequence 5 times. If pressure increased, go to CIRCUIT TEST D19 , step 1) for MPFI and SEFI fuel injected engines. Go to CIRCUIT TEST D19 , step 2) for CFI fuel injected engines. If pressure did not increase, go to next step.
  14. Inertia Switch Check. Turn key off. Locate fuel pump inertia switch and ensure push button on switch is pushed down in the "ON" position. Set DVOM on 200-ohm scale. Measure resistance of switch. If resistance is greater than 5 ohms, replace switch. If resistance is less than 5 ohms, go to CIRCUIT TEST C , step 1).
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