More Likely Causes:
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A faulty CKP sensor prevents the engine from getting the spark timing information it needs, leading to a no-start condition. This is very common on older vehicles.
* Cam Position Sensor (CMP): Similar to the CKP, but for the camshaft. A faulty CMP will also disrupt ignition timing and cause a no-start.
* Distributor (if equipped): Older Rangers might have distributors. Issues within the distributor (rotor, cap, etc.) can disrupt spark delivery to the cylinders. This is less likely on a '99 but still possible.
* Ignition Switch: The switch itself might be failing, preventing power from reaching the ignition system.
* Fuel Pump/Fuel System: The engine might crank but not start if it's not getting fuel. Check the fuel pump relay, fuel pump fuse and the fuel pressure.
* Battery/Alternator: A weak battery or failing alternator can also prevent starting. Check the battery voltage.
* Spark Plugs/Wires: While less likely to cause a complete no-start, worn-out spark plugs or damaged wires can weaken the spark, making starting difficult or impossible.
Less Likely (but still possible) Causes (including your suspicion):
* Coil Pack: A failing coil pack could cause misfires or a complete lack of spark in one or more cylinders. This is more likely to result in a rough running engine or misfires before complete failure.
Troubleshooting Steps:
1. Check the Battery: Test the battery voltage. It should be around 12.6V when not running.
2. Check the Fuses and Relays: Inspect the fuses and relays related to the ignition and fuel systems.
3. Listen for the Fuel Pump: When you turn the key to the "on" position (before cranking), you should hear the fuel pump prime for a second or two. If you don't hear it, there might be a problem with the pump or its circuit.
4. Check for Spark: This requires some basic automotive knowledge and tools, but checking for spark at the spark plugs is a good way to isolate ignition system issues.
5. Have it scanned: The easiest way to diagnose the issue is to take it to a mechanic or auto parts store that can scan for diagnostic trouble codes (DTCs). These codes will point to the most likely problem.
In short: While a faulty coil pack *could* be the problem, it's not the most probable cause given your description. Start with the simpler checks (battery, fuses, fuel pump) and then move on to the sensors and other components. Getting it scanned will save you time and potentially money.
