* Crankshaft Position Sensor (CKP): This sensor is crucial for starting. A failing CKP sensor can cause intermittent starting problems, especially when cold. It's a common failure point on these trucks.
* Fuel Delivery: While less likely given it runs fine once started, check these:
* Fuel Pump: Ensure it's delivering adequate pressure. A weak pump might struggle to prime the system in the cold morning. A fuel pressure gauge test is necessary.
* Fuel Filter: A clogged filter can restrict fuel flow, especially when cold and the fuel is thicker.
* Ignition System:
* Ignition Coil: A weak coil might struggle to generate the necessary spark for cold starts.
* Ignition Wires: Cracked or worn wires can lead to misfires, especially under cold conditions. Check for cracks or damage.
* Distributor Cap and Rotor (if applicable): If your Vortec still uses a distributor, inspect for wear, cracks, or corrosion.
* Coolant Temperature Sensor (CTS): The computer uses the CTS reading to adjust fuel mixture and ignition timing. An inaccurate reading could cause poor starting when cold.
* Battery and Starting System: A weak battery or failing starter motor can cause slow cranking, making it harder to start, especially when cold. Test the battery and starter.
* Air Intake System: Check for any air leaks in the intake system. A leak can cause a lean condition that's more pronounced when the engine is cold.
Why the TP Sensor Replacement Didn't Help: The Throttle Position Sensor (TPS) primarily affects driveability and throttle response *while the engine is running*. It's less likely to be the direct cause of a cold-start issue. Its replacement was probably a shot in the dark based on some generic starting problem advice.
Troubleshooting Steps:
1. Battery and Starting System Test: This is the easiest and cheapest check.
2. Check Fuel Pressure: This is crucial to rule out fuel delivery issues.
3. Inspect Ignition System Components: Look for visible damage or wear on the coil, wires, cap, and rotor (if applicable).
4. Crankshaft Position Sensor (CKP): Given the symptoms, this is a high-probability suspect. Consider replacing it if the other checks don't reveal a problem.
5. Coolant Temperature Sensor (CTS): A relatively inexpensive part to replace and often overlooked.
Important Note: Without diagnostic tools (like a scan tool to read codes), pinpointing the exact cause might be challenging. A scan tool can often reveal trouble codes that point directly to a faulty sensor or system. A mechanic with experience on these vehicles can be helpful in diagnosing the problem efficiently.
