Ignition Cable: Testing and Inspection

PROCEDURE W/ OSCILLOSCOPE

^ Check ignition system with an oscilloscope.

NOTE: When testing secondary cables for damage with an oscilloscope, follow the instructions of the equipment manufacturer.



PROCEDURE W/O OSCILLOSCOPE


If an oscilloscope is not available, spark plug cables may be tested as follows:

1. With the engine running, remove spark plug cable from spark plug (one at a time), and hold next to engine ground. If the cable and spark plug are in good condition, the engine rpm will drop and the engine will run poorly. If engine rpm does not drop, the cable and/or spark plug may not be operating properly and should be replaced.

NOTE: To remove cables from spark plugs, twist the rubber protector boot approximately 1/2-turn to break the seal. Grasp the boot and pull it from the plug with a straight and steady pull. Do not pull on the cable itself. This will damage the conductor and terminal connection. Do not use metal pliers to remove the cable.

CAUTION: Do not leave any one spark plug cable disconnected for longer than necessary during testing. Possible heat damage to the catalytic converter may occur. Total test time must not exceed ten minutes.

2. With the engine not running, connect one end of a test probe to a good ground. Start the engine and run the other end of the test probe along the entire length of all spark plug cables. If cables are cracked or punctured, there will be a noticeable spark jump from the damaged area to the test probe. The cable running from the coil to the distributor cap can be checked in the same manner.

NOTE: Cracked, damaged or faulty cables should be replaced with resistance type cable. These can be identified by the words Electronic Suppression printed on the cable jacket.

3. Use an Ohmmeter to test for open circuits, excessive resistance or loose terminals. Remove the distributor cap from the distributor. Do not remove cables from cap. Remove cable from spark plug. Connect ohmmeter to spark plug terminal of cable, and to corresponding electrode inside of distributor cap. Resistance should be within specifications shown in the Spark Plug Cable resistance chart. If not, remove cable from distributor cap tower and connect ohmmeter to the terminal ends of cable. If resistance is still not within specifications, replace the cable. Test all spark plug cables in this manner.

4. To test coil-to-distributor cap cable, do not remove the cable from the cap. Connect the ohmmeter to the rotor button (center contact) and the terminal at the coil end of the cable. If resistance is not within specifications in the resistance chart, remove cable from distributor cap. Now connect the ohmmeter to the terminal ends of the cable. If resistance is still not within specifications, replace the cable. Inspect the coil tower for cracks or corrosion.

NOTE: To remove cables from the distributor cap or ignition coil tower, loosen the boot first. Grasp the upper part of the boot and the cable. Gently pull straight up.

5. Replace cables one at a time to be sure that the correct firing order is maintained. Route the new cables in the same manner as the original cables, keeping them away from accessory drive pulleys and exhaust manifolds. Secure the cables in their proper retainers.

NOTE: When installing new cables, pinch the protective nipple to release any air trapped between the tower and nipple.