Battery Related:
* Weak Battery: This is the most common cause. Cold weather significantly reduces battery performance. Get it tested at an auto parts store. A load test is crucial, not just a voltage check.
* Corroded Battery Terminals: Clean the terminals with a wire brush and baking soda solution. Loose connections can also prevent sufficient current flow.
* Alternator Issues: While the alternator charges the battery *while the engine is running*, a failing alternator may not be charging adequately overnight, leaving the battery depleted by morning. Have it tested as well.
Starting System:
* Starter Motor: A weak or failing starter motor struggles to crank the engine, especially when cold. You might hear a slow crank or a clicking sound.
* Solenoid: The solenoid is part of the starter motor; a faulty one prevents the starter from engaging. You might hear a clicking sound when you turn the key.
Fuel System:
* Fuel Pump: A weak fuel pump may not deliver enough fuel to the engine when cold. This is less likely if it runs fine once started.
* Fuel Filter: A clogged fuel filter restricts fuel flow.
* Fuel Injectors: Clogged or failing injectors can lead to poor cold-start performance. This is more likely if you have other drivability issues.
Ignition System:
* Distributor Cap and Rotor: These wear out over time. Cracks or corrosion can prevent a good spark, especially when cold.
* Ignition Coil: A weak or failing ignition coil reduces spark strength.
* Spark Plugs and Wires: Worn or fouled spark plugs or cracked/worn wires can prevent proper ignition.
Other Possibilities:
* Glow Plugs (Diesel Only): If you have a diesel Wrangler (unlikely for a '94, but possible), failing glow plugs are a major cold-starting issue.
* Sensor Issues: Various sensors (like the crankshaft position sensor or temperature sensor) can affect starting. A faulty sensor sends incorrect information to the engine's computer, leading to poor starting.
Troubleshooting Steps:
1. Battery Test: This is the absolute first step. Have the battery and alternator tested at an auto parts store.
2. Clean Battery Terminals: Always a good idea.
3. Check for Obvious Issues: Inspect the obvious parts like wires, connections, and the starter motor for any visible damage.
4. Listen Carefully: Pay attention to the sounds your Jeep makes when you try to start it. A slow crank, clicking, or unusual noises provide clues.
Recommendation:
Unless you're experienced with auto repair, it's best to have a mechanic diagnose the problem. Attempting to fix these issues without proper knowledge can lead to further damage or injury. Starting with a battery and alternator test is the cheapest and easiest first step.
