1. Ignition Coil Temperature Test:
* The Problem: Ignition coils can degrade with heat. They might function fine when cold but fail as they heat up during a hot day's driving.
* The Test: You'll need a multimeter. With the engine hot (after a drive on a warm day), carefully check the resistance of the primary and secondary windings of the ignition coil according to your car's specifications (found in a repair manual or online). Compare this to the coil's specifications. A significant deviation indicates a problem. Also, physically inspect the coil for any cracks or signs of damage.
2. Distributor Cap and Rotor (if applicable):
* The Problem: Cracks or carbon buildup in the distributor cap and rotor can impede spark delivery, especially when components expand with heat.
* The Test: Visually inspect the distributor cap and rotor for cracks, carbon tracking, or corrosion. Clean them thoroughly with a contact cleaner (specifically designed for electrical components). Replace if damage is found.
3. Ignition Control Module (ICM) / Ignition Control Unit (ICU):
* The Problem: The ICM/ICU controls the ignition coil. A failing ICM/ICU can cause intermittent spark issues, often exacerbated by heat. This is particularly relevant if your car doesn't have a distributor.
* The Test: This requires more advanced diagnostic tools, ideally an OBD-II scanner that can read live data and fault codes related to ignition timing or sensor failures. A mechanic with a scan tool can usually diagnose ICM/ICU problems.
4. Crankshaft Position Sensor (CKP) / Camshaft Position Sensor (CMP):
* The Problem: These sensors tell the ignition system when to fire the spark plugs. A faulty sensor, particularly one affected by heat, can cause erratic or absent spark.
* The Test: Often requires an OBD-II scanner to check for fault codes relating to these sensors. Visual inspection for damage or corrosion is also a good first step.
5. Wiring and Connections:
* The Problem: Loose, corroded, or damaged wiring in the ignition system can disrupt spark delivery. Heat can exacerbate these problems.
* The Test: Carefully inspect all wiring related to the ignition coil, distributor (if applicable), sensors, and ignition switch. Look for any loose connections, frayed wires, or corrosion. Clean or repair any problems found.
Troubleshooting Steps:
1. Start with the simplest and cheapest tests: Visual inspection of the distributor cap and rotor, and checking wiring and connections.
2. Then move to the ignition coil temperature test. This is relatively easy and can pinpoint a common heat-related failure.
3. Use an OBD-II scanner if available. This can reveal fault codes that provide valuable clues.
4. If all else fails, consult a mechanic. They have the tools and expertise to diagnose more complex issues like the ICM/ICU, crankshaft/camshaft position sensors, or other less common causes.
Replacing the ignition coil and distributor should be a last resort. Systematic testing will help you pinpoint the exact problem and avoid unnecessary expense. Remember to always disconnect the battery's negative terminal before working on any electrical components.
