The spark plug cable is a simple but essential element of the engine. It carries to the spark plug a current with high potential difference (30000-50000 volts) which is generated by the ignition coil. When exposed to vibration and heat, the carbon in the cable may loosen and lose its conductivity between the coil and the spark plug. To ensure optimum engine performance, you should periodically replace these cables. In this tutorial we will describe how to test them, so you can diagnose or avoid some problems, including engine misfire and static discharges in the car stereo.
Steps
Step 1. Check for signs of malfunction
When the spark plug wires begin to deteriorate, special characteristics arise, including:
- The engine idles roughly.
- The engine will not start.
- Interference can be heard when you listen to the car stereo.
- Consumption increases.
- The exhaust smoke test fails due to high hydrocarbon emissions or a failure of a cylinder is detected.
- The engine light comes on.
Step 2. Inspect the spark plug wires
Use a flashlight or park your car in a well-lit area to check them out.
- Look for any obvious damage on the cables themselves or on the spark plug inserts; make sure there are no cuts or burn marks.
- Check the cables and examine the insulating sheath that surrounds them.
- Look for damage caused by the high heat emitted by the engine block (burn marks).
- Inspect the spark plug and coil couplings for corrosion.
Step 3. Start the engine
Watch for arcing or listen for sudden pops. Both indicate a high voltage electrical leak.
Step 4. Use an electric battery wire to ground a screwdriver with an insulated handle
Run the screwdriver over each spark plug lead, around the coil and over the connectors. If you notice an arcing between the screwdriver and the cable, then the cable has deteriorated.
Step 5. Take a spray bottle full of water and spray the cables
Especially wet the area around the connections to the candles to observe the possible formation of electric arcs and mist. If this test is positive, turn off the engine. Detach the connector from the spark plug and check it inside for traces of carbon. If so, you will need to change the spark plug as well.
Step 6. Check the resistance of the cables
If the spark plugs and cables are the original ones from the car manufacturer, find the resistance value in the vehicle's user and maintenance manual. If you have already replaced them and they are no longer the original ones, you can do an online search to get the data.
Use an ohmmeter to determine if the resistance of the leads matches the recommended resistance. Secure the probes to the ends of the cable making sure they touch the metal contacts. Check on the instrument that the resistance is within the range recommended in the manual
Step 7. Inspect the spring clips securing the wires to the distributor
If these items are damaged, then the cables may move out of their correct position.
Step 8. See if the cables are properly mounted
Consult the maintenance manual to find the reference chart and complete this inspection. If the cables cross, they could cause charge leakage.
Advice
- Do not disconnect the cables all together; remove them one at a time and reconnect them before moving on to the next.
- Keep spark plugs clean to reduce dissipative charge loss.
- Some engines have a particular configuration of the ignition coil which completely excludes the spark plug cables although the connector is still present.
- Do not assume that cross-wiring is a bad signal. Some car manufacturers do this to cancel out magnetic fields.
