Timing Related Issues (Even if you think it's right):
* Incorrect Timing: This is the most likely culprit. Even experienced mechanics can mistime a chain. Double and triple-check your timing marks. A single tooth off can prevent the engine from starting, or cause catastrophic damage if run. Consult a repair manual specific to your engine to ensure you have the correct top dead center (TDC) and camshaft alignment.
* Bent Valves: If the timing was significantly off before the repair, you might have bent valves. This is a common consequence of running an engine with incorrect timing. A compression test will reveal bent valves (low or no compression in one or more cylinders).
* Broken Timing Chain Tensioner or Guide: A faulty tensioner or guide might not allow the chain to maintain proper tension, leading to improper timing.
Non-Timing Related Issues:
* Distributor Issues (if applicable): On some S-10s, the distributor needs to be correctly aligned with the timing chain. Make sure the distributor is properly seated and the rotor is pointing at the correct cylinder for the #1 cylinder firing position.
* Crank Sensor: A faulty crankshaft position sensor prevents the engine from knowing where the crankshaft is, preventing proper ignition timing.
* Cam Sensor: Similar to the crank sensor, a bad camshaft position sensor will prevent starting.
* Ignition System Problems: Check the ignition coil, spark plugs, plug wires, and ignition module. A weak spark can prevent starting. Test the spark at each plug to confirm good ignition.
* Fuel System Problems: Make sure you have fuel pressure. Check the fuel pump, fuel filter, and fuel injectors.
* Battery and Starter: Verify the battery has sufficient charge and the starter is working correctly. A weak battery or faulty starter will also prevent starting.
* Security System (if equipped): Some vehicles have security systems that can prevent starting if there's a problem with the system.
* Neutral Safety Switch: This switch prevents starting unless the vehicle is in park or neutral. Make sure the transmission is in the correct gear.
Troubleshooting Steps:
1. Recheck the Timing: This is the absolute first step. Carefully verify your timing marks again.
2. Compression Test: This helps determine if you bent valves.
3. Check for Spark: Test each spark plug wire individually for spark.
4. Check Fuel Pressure: Verify fuel is reaching the injectors.
5. Inspect the Crankshaft and Camshaft Sensors: Check for damage or poor connection.
6. Test the Ignition Coil: Ensure it's putting out the required voltage.
If you're not comfortable performing these checks yourself, take it to a qualified mechanic. Diagnosing starting issues can be complex, and an incorrect diagnosis can lead to further damage or unnecessary expense. Trying to start the engine repeatedly with incorrect timing will likely cause serious engine damage.
