Investigating wiring problems
[dropcap]A[/dropcap]t Cyclepedia.com we provide technical support to our members using our online manuals to service and repair vehicles. On a regular basis we get a service ticket from a member saying, “I’ve replaced my ignition coil, ECM and/or some other expensive part and I still don’t have spark. What should I do?” This is frustrating for the member and our tech support team. For the member, they have needlessly spent money to replace expensive parts and aren’t any better off for it. For the Cyclepedia crew, we wish we could have helped when the initial problem surfaced to avoid unnecessary blind part replacement.
1. It is extremely rare for a no spark condition to be the result of a faulty coil or ECM. Users get fixated on these items and jump to the conclusion they must be responsible for their problem because these items are easy to see and replace. This is the opposite of the strategy needed to fix a no spark condition. When taking on a no spark condition one needs to be patient and have an open mind. Becoming fixated on specific components is a good way to not find the true problem. It’s far more likely that there is a problem with a wire, connector, ground, or switch than an actual ignition system component, but only assume the fault could be anywhere so don’t focus on a single item until testing indicates that item may be faulty.
2. Start at the beginning and don’t jump ahead. If the vehicle is equipped with a battery make sure it is fully charged. An under charged battery can result in slow cranking speed that will not be optimal for the ignition system. Check the condition of the main and ignition fuses. Make sure the switches in the ignition system are connected and are in the correct position for ignition system operation.
3. When checking for spark, fit a new spark plug into the plug cap and ground this new plug to the engine. Make sure there isn’t any water in the spark plug cap. Leave the old plug in the head for proper compression. Do not touch the spark plug or wire while cranking or running the engine as this can result in a severe shock. Crank the engine and observe the spark plug for spark. If there is spark examine and replace the old spark plug as necessary. If the engine is a multi-cylinder make sure the spark plug caps and wires are installed to the correct cylinders – check the ignition timing if necessary.
4. It is time to start troubleshooting and testing the ignition system now that the no spark condition has been confirmed. It is important to check the connectors and wiring as you work through the system. There may be a loose connector or faulty connector wiring that is disrupting the circuit. Check for corrosion and poor fitment between male and female wiring terminals. Check grounds for solid connections.
5. Use the wiring diagrams to aid in wiring inspection. Any ground wire should have continuity to a ground. Non-ground wires shouldn’t have continuity with a ground, but they should have continuity with themselves at other places in the wiring harness. For example a blue/white signal wire from the pickup coil needs to have continuity between its terminal where it connects to the harness from the coil, and its terminal where the harness connects to the ECM. If the wire doesn’t have continuity on both sides of the harness there is an open circuit and the ignition system will act as if the pickup coil is faulty though it is actually a wiring problem.
Part 2 of dealing with no spark ignition system problems will go further into detail on component inspection. Faulty components are more rare than a wiring problem or other outlying issues, but they do happen and the manufacturers provide testing instructions. No spark issues are common, frustrating problems. Remember to be patient and inspect the full system, not just the main components.