Diagnostic Aids

WARNING: This page is about a different car, the 1994 Mercury Sable, 1994 Mercury Cougar, 1994 Lincoln Continental, 1994 Ford Thunderbird, and 1994 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test only when instructed by QUICK TEST or directed here by a driveability symptom. This test is only intended to diagnose:

Wiring harness circuits (VPWR and IMRC).
Intake Manifold Runner Control (IMRC) solenoid.
Faulty Powertrain Control Module (PCM).

To prevent replacing good components, check the following non-EEC areas for faults:

Vacuum tank leaks.
Vacuum hose leaks.

Fig 1: IMRC Circuit (KT1)

1) Code 551: Check IMRC Solenoid Resistance Code 551 indicates IMRC solenoid output voltage did not change when IMRC was activated during KOEO SELF-TEST. Possible causes for this fault are:

IMRC circuit open or shorted.
Faulty IMRC solenoid.
PCM output driver open or grounded.

Turn ignition off. Disconnect IMRC solenoid wiring harness connector. Measure resistance between IMRC solenoid terminals. If resistance is not 50-100 ohms, replace solenoid and repeat QUICK TEST. If resistance is 50-100 ohms, go to next step.

2) Check Voltage Of VPWR Circuit Turn ignition on. Measure voltage between VPWR terminal of IMRC solenoid wiring harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open circuit and repeat QUICK TEST.

3) Check Continuity Of IMRC Solenoid Circuit Turn ignition off. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 32 at breakout box and IMRC terminal of IMRC solenoid wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components, and repeat QUICK TEST. and repeat QUICK TEST.

4) Check IMRC Circuit For Short To Ground Turn ignition off. Measure resistance between test pin No. 32 and test pins No. 40, 46 and 60. If all readings are more than 100,000 ohms, go to next step. If any reading is 100,000 ohms or less, repair short circuit. Remove breakout box, reconnect all components, and repeat QUICK TEST.

5) Check IMRC Circuit For Short To Power Turn ignition off. Measure resistance between test pin No. 32 and test pins No. 37 and 57 at breakout box. If all readings are 100,000 ohms or more, replace PCM and repeat QUICK TEST. If any reading is less than 100,000 ohms, repair short circuit and repeat QUICK TEST. If fault is still present, replace PCM. Repeat QUICK TEST.

6) Check IMRC Valves Turn ignition off. Disconnect vacuum lines from both IMRC valves. Use vacuum pump to apply 10 in. Hg vacuum to each IMRC valve. If both valves hold vacuum, go to next step. If valve(s) do not hold vacuum, replace valve as necessary and repeat QUICK TEST.

7) Check Operation Of IMRC Valves Apply 10 in. Hg to each air valve. If both valves and mechanical linkage move in response to applied vacuum, go to next step. If valves and/or linkage do not move, repair as necessary and repeat QUICK TEST.

8) Check Vacuum IMRC Valves Check vacuum lines from IMRC valves to solenoids. Inspect vacuum lines for damage and blockage. If vacuum lines are damaged or blocked, repair as necessary. If vacuum lines are okay, go to next step.

9) Enter OUTPUT STATE CHECK Use only VOM or DVOM for this step. DO NOT use scan tester. Turn ignition off. Disconnect cruise control servo wiring harness connector. Connect DVOM negative lead to STO terminal at Data Link Connector (DLC). See Figure. Connect positive lead to positive battery terminal. Install a jumper wire between STI terminal and SIG RTN terminal at DLC. Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than 1.0 volt when test is complete to indicate PCM has entered OUTPUT STATE CHECK. Depress and release throttle. If voltage increases, remain in OUTPUT STATE CHECK and go to next step. If voltage does not increase, depress throttle to WOT and release. If voltage does not go high, go to CIRCUIT TEST QC.

10) Check IMRC Solenoid Electrical Operation Turn ignition off. Disconnect IMRC solenoid wiring harness connector. Connect DVOM positive lead to connector VPWR terminal. Connect negative lead terminal IMRC at IMRC connector. Observe DVOM while cycling throttle open and closed. If DVOM does not cycle 0.5 volt or more, return to step 1). If DVOM does cycle 0.5 volt or more, go to next step.

11) Check IMRC Solenoid Vacuum Disconnect IMRC solenoid vacuum hose and wiring harness connector. Turn ignition on. Use vacuum pump to apply 16 in. Hg vacuum to each IMRC valve. If vacuum is not held for 20 seconds, replace solenoid and repeat QUICK TEST. If vacuum is held, go to next step.

12) Check IMRC Solenoid Mechanical Operation Remain in OUTPUT STATE CHECK. Using vacuum pump, apply 16 in. Hg vacuum to each IMRC valve. Depress and release throttle. If vacuum is not released, replace solenoid and repeat QUICK TEST. If vacuum is released, go to next step.

13) Disconnect IMRC solenoid vacuum hose. Start engine. Check vacuum at disconnected hose. If vacuum is present at hose, system is okay. If vacuum is not present, check supply hose to IMRC solenoid. Repair as necessary, and repeat QUICK TEST.