Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. To prevent replacement of good components, be aware following non-EEC related areas may be at fault.

Excessive blow-by
PCV malfunction
Vacuum leaks
Incorrect fuel pressure
Throttle binding This test is only intended to diagnose following.
Throttle Position (TP) sensor
Mass Airflow (MAF) sensor
Intake Air Temperature (IAT) sensor
Fuel injectors

1) Continuous Memory Code 121: TP Sensor Integrity Code 121 indicates TP sensor is inconsistent with MAF value. Turn ignition off. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Connect DVOM to test pins No. 46 and 47. Slowly apply throttle to WOT, and release to closed position. Voltage should change smoothly from 0.4 volt to 4.5 volts. See CIRCUIT TEST DH for schematics and specific engine values. If voltage change is incorrect or erratic, ensure TP sensor is properly installed. If TP sensor is properly installed, replace TP sensor and repeat QUICK TEST. If voltage is okay, go to step 7) for Code 121 or next step for all other codes.

2) Check Idle Ensure idle is correct. If idle is correct, go to next step. If idle is incorrect, see IDLE SPEED in ADJUSTMENTS article in the ENGINE PERFORMANCE section.

3) Check Throttle Body Check throttle and/or cruise control linkage for binding and rough operation. Inspect throttle body for sludge build-up. Check engine vacuum hoses. Refer to Vehicle Emission Control Information (VECI) decal for proper vacuum hose routing. Check for air leak between ISC solenoid and MAF sensor. If problems are found, repair as necessary and repeat QUICK TEST. If no problems are found, go to step 5).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 5). No test procedures have been omitted.

5) Check IAT Sensor Ensure ambient temperature is more than 50°F (10°C) before performing this test. Check and repair any air leaks in front of IAT sensor. Turn ignition off. Connect breakout box to PCM. Set DVOM to 20-volt scale. Connect DVOM to test pins No. 25 and 46. Start engine and let it idle. Observe voltage as engine warms. See CIRCUIT TEST DA for voltage specifications. If voltage decreases smoothly and stabilizes when engine reaches operating conditions, system is operating properly at this time. Testing is complete. If voltage does not decrease smoothly and stabilize after engine reaches operating conditions, replace IAT sensor and repeat QUICK TEST.

6) Continuous Memory Code 184 Or 185: Inspect MAF Sensor Code 184 indicates MAF sensor signal is higher than expected. Code 185 indicates MAF sensor signal is lower than expected. Turn ignition off. Check for air leaks between Idle Air Control (IAC) solenoid and MAF sensor. Inspect MAF sensor for oil contamination caused by excessive blow-by or malfunctioning PCV. If problems are found, repair as necessary. Clear codes, and repeat QUICK TEST. If all checks are okay, go to step 9).

7) Check MAF Sensor Circuit Voltage Turn ignition off. Disconnect PCM 60-pin connector. Inspect and repair any damaged terminals. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Start engine and warm to normal operating temperature. Measure voltage between MAF test pin and test pins No. 40 and 60 at breakout box. See MAF WIRE COLOR & TEST PIN IDENTIFICATION table. If voltage is not within specification, replace MAF sensor and repeat QUICK TEST. See MAF SENSOR DATA table. If voltage is within acceptable range, system is operating normally at this time. See SUMMARY.

MAF WIRE COLOR & TEST PIN IDENTIFICATION

Application	Wire Color	Test Pin No.
Navajo	Light Blue/Red	50

MAF SENSOR DATA

Engine Condition

⁽¹⁾ Voltage

Idle

0.8

20 MPH

1.0

40 MPH

1.7

60 MPH

2.1

⁽¹⁾	With engine at normal operating temperature.

8) Continuous Memory Code 186 Or 187: Visual Vacuum Checks Code 186 indicates pulse width is lower than expected (rich). Code 187 indicates pulse width is higher than expected (lean). Inspect air cleaner and air inlet duct. Replace or repair an necessary. Check for unmetered air leaks between MAF sensor and IAC solenoid. Check all engine vacuum hoses for damage, blockage and improper routing. Make necessary repairs, and repeat QUICK TEST. If all checks are okay, go to next step.

9) Check Fuel Pressure Turn ignition off. Install fuel pressure gauge. Ensure vacuum hose is connected to fuel pressure regulator (if applicable). Start and run engine at idle. If fuel pressure is within specification, go to next step. See FUEL PRESSURE SPECIFICATIONS table. If fuel pressure is not within specification, repair as necessary. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE section.

FUEL PRESSURE SPECIFICATIONS ⁽¹⁾

Engine

KOER: psi (kPa)

KOEO: psi (kPa)

Navajo

45-60 (310-415)

50-60 (345-415)

⁽¹⁾	Volume is 1 Pt. (.5L) in 30 Seconds.

10) Verify Fuel Pressure Retention Ability Turn ignition on. If fuel pressure remains at specification for 60 seconds, go to next step (SFI) or CIRCUIT TEST H, step 7) (MFI). If fuel pressure does not remain at specification, repair fuel delivery system as necessary. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE section.

11) Cylinder Balance Test Perform KOER SELF-TEST. After last code, wait 5-10 seconds, and then goose throttle lightly (not wide open throttle). This will activate cylinder balance test. If Code 90 is present after test, go back to step 6). If Code 90 is not present after test, go to CIRCUIT TEST H, step 4).