Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. (Fuel-contaminated engine oil may affect Codes 41/172, 91/136, 42/173 and 92/137. If fuel-contaminated engine oil is suspected, remove PCV valve from valve cover and repeat QUICK TEST). If problem is corrected, change engine oil and filter. Only use this test to diagnose:

• HO2S and sensor connection.
• Vacuum systems.
• Fuel injector and/or fuel injector circuitry.
• Powertrain Control Module (PCM).
• Electrical circuits (HO2S, HO2S GND, INJ 1-8, VPWR and SIG RTN).

To prevent replacement of good components, be aware the following non-EEC areas may be cause of driveability concerns:

• Ignition system.
• Faulty evaporative emission system.
• EGR and/or PCV system.
• Air intake system.
• Engine oil contamination.
• Fuel system.
• Intake, supercharger, or charge air cooler leaks.
• Exhaust system leaks or restriction.
• Electrical system.
• Secondary air injection system.
• Engine cooling system.

Engine	Ohms
All Models	11-18

Engine	Ohms
2.3L	6.0-8.5
3.0L	4.0-5.5
5.0L	3.0-4.0

Application		Wire Color
3.0L		Red/Black
3.8L
Cougar & Thunderbird		Tan/White
Sable & Taurus		Red/Black

Application		Wire Color
3.0L		Dark Blue/Light Green
3.8L
Cougar & Thunderbird		Tan/Orange
Sable & Taurus		Dark Blue/Light Green

Application	Wire Color
4.6L	Red/Black
5.0L (Cougar & Thunderbird)	Tan/White

Application	Wire Color
4.6L	Gray/Light Blue
5.0L (Cougar & Thunderbird)	Tan/Orange

Acronym	Definition
HO2S	Heated Oxygen Sensor
MFI	Multiport Fuel Injection
SFI	Sequential Multiport Fuel Injection

1) Check For Contaminated Engine Oil  Turn ignition off. Remove PCV valve from valve cover. Inspect PCV system for damage. Inspect valve for blockage and movement of valve plunger. Repair as necessary. Perform KOEO and KOER SELF-TEST. Service ignition continuous memory code (if present) before KOER codes. If vehicle is a no-start, KOER Code 41/172, 42/173, 91/136 or 92/137 or Continuous Memory Code 171, 172, 173, 174, 175, 176, 177, 178, 41/144 or 91/139 is set, install PCV valve and go to step 2). If no codes are set, change engine oil and filter. Install PCV valve, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

2) Check Fuel Pressure  Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Ensure manifold vacuum supply is connected to fuel pressure regulator (if equipped). Run engine at idle and check fuel pressure. If vehicle will not start, cycle ignition on and off several times. Check fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to step 3). If pressure is not within specification, go to FUEL SYSTEM in I - EEC-IV SYS/COMP TESTS article in this section.

3) Check System Ability To Hold Fuel Pressure  Turn ignition on. Check fuel system for leaks. Repair or replace as necessary. If fuel system does not leak and pressure remains at specification for 60 seconds, go to step 4) (no-starts), step 5) (MFI) or step 6) (SFI).

4) Fuel Delivery Test  Release fuel system pressure. With fuel pressure gauge installed, pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, EEC-IV system is not causing no-start condition. Check additional no-start tests in TESTS W/O CODES article in this section. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge. Connect inertia switch. Go to step 7) for MFI or step 8) for SFI.

5) Cylinder Balance Test (MFI)  Connect a tachometer to engine. Start engine, and run it at idle. Disconnect and reconnect injectors individually, noting RPM drop as each injector is disconnected. IAC motor will attempt to re-establish RPM. If each injector does not produce a momentary drop in RPM, go to step 7). If each injector produces a momentary drop in RPM, go to step 13) for Codes 41/172, 91/136 or 176, step 24) for Codes 42/173, 92/137 or 177 or step 14) for all others.

6) Cylinder Balance Test (SFI)  Perform KOER SELF-TEST. After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST by lightly goosing throttle (not WOT). Test time is about 2-3 minutes. To interpret codes retrieved from test, refer to CYLINDER BALANCE TEST SERVICE CODES table. If fault codes are present, go to step 8). Code 77/538 indicates throttle was touched when test was ran and test is not completed. Code 538 could also be output if Continuous Memory Code 214 (CID) is present. If Continuous Memory Code 214 is present, see appropriate chart under SERVICE CODE-TO-TEST MENUS for instruction. For symptoms or Code 41/172, 91/136 or 176, go to step 13). For Code 42/173, 92/137 or 177, go to step 24). For all other codes, go to step 14).

Service Code	Application
90	Pass
10	Cylinder No. 1
20	Cylinder No. 2
30	Cylinder No. 3
40	Cylinder No. 4
50	Cylinder No. 5
60	Cylinder No. 6
70	Cylinder No. 7
80	Cylinder No. 8
77/538	Retest

7) Check Injector & Harness Resistance (MFI)  Turn ignition off. Wait 10 seconds. Disconnect PCM 60-pin connector. Inspect pins for damage. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance of injector bank No. 1 between test pins No. 37 and 58 at breakout box. Measure resistance of injector bank No. 2 between test pins No. 37 and 59 at breakout box. Record resistances. Refer to INJECTOR BANK RESISTANCE table in this circuit test. If each resistance is within specification, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to step 9) for all other conditions.

8) Check Injector & Harness Resistance (SFI)  Turn ignition off and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect pins for damage. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure and record resistance between suspected injector circuit test pin and test pin No. 37. For no-start, measure and record resistance between injector circuit test pin and test pin No. 37. Refer to INJECTOR BANK RESISTANCE table in this circuit test. If each resistance is within specification, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to step 9) for all other conditions.

9) Check Continuity Of Fuel Injector Harness  Turn ignition off. Disconnect injector wiring harness connector at injectors. Set DVOM to 200-ohm scale. Measure resistance between test pins No. 37 and 57 atbreakout box and each injector VPWR terminal at wiring harness connector. See Figure-58. Measure resistance between injector test pin(s) at breakout box and same injector circuit terminal at each injector wiring harness connector. If each resistance is less than 5 ohms, go to step 10). If each resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

10) Check Injector Harness Ckt For Short To Power Or Ground  Turn ignition off, and wait for 10 seconds. With breakout box installed and PCM disconnected, disconnect fuel injector wiring harness connector. See Figure-58. Measure resistance between injector test pin(s) and test pins No. 37, 40, 46, 57 and 60. Measure resistance between injector test pin(s) at breakout box and chassis ground. If each resistance is 10,000 ohms or more, replace injector per cylinder balance test service code and repeat QUICK TEST (SFI) or go to next step (MFI). If each resistance is less than 10,000 ohms, repair short. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

11) Isolate Faulty Injector Circuit  Turn ignition off. Install breakout box, and disconnect PCM. Disconnect all injectors on suspect bank. With DVOM set on 200-ohm scale, connect one injector and measure resistance between test pins No. 37 and 58 (injector bank No. 1) or 59 (injector bank No. 2). Disconnect injector, and repeat process for all other injectors. See INDIVIDUAL INJECTOR RESISTANCE table. If all injectors are within specification, go to step 12). If injectors are not as specified, replace injector. Remove breakout box, and reconnect components. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

12) Check Injector Drive Signal  With ignition off and breakout box installed, connect PCM to breakout box. Use a non-powered 12-volt test light, and connect as follows:

Because MAP sensor greatly influences fuel control, MAP sensor may malfunction without setting Code 22/126. Next 2 steps test MAP vacuum circuit.

28) Check MAP Sensor For Vacuum Leaks  Turn ignition off. Disconnect vacuum hose from MAP sensor. Inspect hose for damage and repair as necessary. Connect vacuum pump to sensor. Apply 18 in. Hg to MAP sensor. If sensor does not hold vacuum, replace MAP sensor. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST. If sensor holds vacuum, release vacuum and go to step 29).

29) Check For Loss Of Vacuum To MAP Sensor  Using vacuum "T", connect vacuum gauge in MAP sensor vacuum circuit. Start engine. Note vacuum reading after idle stabilizes. Turn ignition off. Remove "T" and vacuum gauge. Reconnect hose to MAP sensor. Connect vacuum gauge at a different manifold vacuum location. Start engine, and note vacuum reading. If readings do not differ by more than 1 in. Hg, go to next step. If readings differ by more than 1 in. Hg, inspect vacuum hoses for leaks, kinks and blockage. Repair as necessary. Connect all components, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

30) HO2S Check  Turn ignition off. Disconnect HO2S. For 4-wire HO2S, connect DVOM to HO2S terminal and HO2S GND or SIG RTN terminal at HO2S connector. For 3-wire HO2S, connect DVOM to HO2S terminal at HO2S connector and negative battery terminal. On all models, cause a vacuum leak to force HO2S to go lean. Remove PCV valve hose. Start engine. Raise engine speed to about 2000 RPM. DVOM should indicate less than 0.4 volt within 30 seconds. If voltage is not as specified, replace HO2S. Reconnect vacuum hoses, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST. If voltage is as specified, go to step 90).

90) Check Continuous Monitor Mode  Start engine, and warm it to normal operating temperature. Raise engine speed to 2000 RPM for 2 minutes and then return to idle. Enter KOER wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. While observing DVOM or scan tester, shake or bend small sections of wiring harness from HO2S to PCM. Wiggle, shake or bend small sections of wiring harness from HO2S GND to PCM. If no fault is indicated, remain in CONTINUOUS MONITOR MODE and go to step 91). If fault is indicated, isolate and repair fault as necessary. Clear codes. Repeat QUICK TEST.

91) Continuous Monitor Test Drive Check  While still in KOER wiggle test, test drive vehicle for 5 miles at 55 MPH over smooth roads. Drive an additional 5 miles at 55 MPH over rough roads. If possible, drive vehicle through a pool of water to wet HO2S and connector. If fault is indicated, isolate fault and repair as necessary. Clear codes, and remove breakout box. Repeat QUICK TEST. If no codes are indicated, exit KOER wiggle test and go to next step.

92) Check HO2S Switching  Turn ignition off. Inspect wiring harness for proper routing and insulation. Check for burnt, chaffed or open wires. Repair if necessary. Disconnect PCM 60-pin connector, and inspect it for damaged or pushed-out pins, corrosion and other damage. Repair as necessary. Install breakout box. Connect PCM to breakout box. Connect analog voltmeter to suspect HO2S test pin and HO2S GND at breakout box. Test drive vehicle for 5 miles at 55 MPH while observing voltmeter. HO2S should switch from .3 volt to .9 volt within 3 seconds. If HO2S does not switch as described, replace HO2S. Connect all components, and repeat QUICK TEST. If HO2S switches as described, fault cannot be identified or duplicated at this time. See INTERMITTENTS in TESTS W/O CODES article in this section.