Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Windstar and 1995 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the exhaust system and downstream HO2S.

Internal damage of a catalytic converter is usually caused by abnormal engine operation upstream of catalyst. Conditions that produce higher than normal temperatures in the catalytic converter, such as cylinder misfire, are likely suspects.

MISFIRE TROUBLE CODES

Service Code

Application

P0300

⁽¹⁾

P0301

Cylinder No. 1 (Test Pin No. 75)

P0302

Cylinder No. 2 (Test Pin No. 101)

P0303

Cylinder No. 3 (Test Pin No. 74)

P0304

Cylinder No. 4 (Test Pin No. 100)

P0305

Cylinder No. 5 (Test Pin No. 73)

P0306

Cylinder No. 6 (Test Pin No. 99)

P0307

Cylinder No. 7 (Test Pin No. 72)

P0308

Cylinder No. 8 (Test Pin No. 98)

⁽¹⁾	Multiple cylinder misfire or faulty CKP sensor.

1) DTC P0420 & P0430: Check Possible Cause Of Misfire

DTC P0420 indicates bank one catalyst system efficiency is minimum requirement. DTC P0430 indicates bank 2 catalyst system efficiency is minimum requirement. Possible causes are as follows:

Use of leaded fuel.
Oil contamination.
Cylinder misfire.
Fuel pressure too high.
HO2S sensor improperly connected.
Damaged exhaust system component.
Faulty ECT sensor.
Faulty HO2S.

Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code(s) is not present, go to next step. If misfire code(s) is present, isolate cylinder and repair as necessary.

2) Check HO2S Monitor DTCs

If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes were present in step 1), go to next step.

3) Check ECT Sensor DTCs

If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes were present in step 1), go to next step.

4) If any codes except P0420 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step.

5) Check Rear HO2S Wiring Harness

Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step.

6) Check Fuel Pressure

Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC.

7) Check For Exhaust System Leaks

If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step.

8) Check For Exhaust System Restrictions

Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step.

9) Check Manifold Vacuum

Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11).

10) Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non-restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step.

11) Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST.

12) Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.