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 following:

Spark plugs.
Spark plug wires.

MISFIRE TROUBLE CODES

Service Code	Application
90	Pass
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) Check Possible Cause Of Misfire

Connect engine oscilloscope to vehicle. View parade pattern of ignition secondary system. Go to next step.

2) Start engine. Normal spark output voltage is 20,000 volts. Maximum spark output variation is 8000 volts. If spark output is not as specified, go to next step. If spark output voltage is as specified, testing is complete. Go to CIRCUIT TEST HD, step 8).

3) If average spark output voltage is more than 20,000 volts with spark output variation less than 8000 volts, check spark plugs for wear and spark plug wires for 7000 ohms per foot maximum resistance. If spark output voltage is not as specified, go to next step.

4) If spark output voltage variation is more than 8000 volts, check spark plugs for wide gap or worn electrode. If spark output voltage variation is less than 8000 volts, go to next step.

5) If spark output voltage is consistently high in selected cylinders only, check for defective spark plug or wire. If spark output voltage is not as specified, go to next step.

6) If spark output voltage is consistently low in all cylinders, check spark plugs for narrow gap and spark plug wires for grounding. If spark output voltage is not as specified, go to next step.

7) If average spark output voltage is 15,000 volts or less with spark output variation less than 5000 volts, testing is complete. Go to CIRCUIT TEST HD, step 8). If spark output voltage is not as specified, go to next step.

8) If average spark output voltage is more than 15,000 volts with spark output variation less than 5000 volts, check spark plugs for wear and spark plug wire for 7000 ohms per foot maximum resistance. If spark output voltage is not as specified, go to next step.

9) If spark output voltage variation is more than 5000 volts, check spark plugs for wide gap or worn electrode. If spark output voltage variation is less than 5000 volts, go to next step.

10) If spark output voltage is consistently high in selected cylinders only, check for defective spark plug or wire. If spark output voltage is not as specified, go to next step.

11) If spark output voltage is consistently low in all cylinders, check spark plugs for narrow gap and spark plug wires for grounding. If spark output voltage is not as specified, ignition secondary system is okay and testing is complete.