1. Compression Test: This is the most crucial step. If you have spark and fuel, but the engine doesn't fire, low compression is a leading suspect. A compression test measures the pressure in each cylinder when the engine is cranked. Low compression in one or more cylinders indicates issues like:
* Worn piston rings: Allowing compression to escape.
* Burnt valves: Preventing proper sealing.
* Head gasket leak: Allowing compression to escape into the cooling system or crankcase.
* Cracked head or block: A more serious mechanical issue.
2. Timing Belt/Chain: A jumped or broken timing belt (or chain, depending on the engine) will prevent the engine from firing, even with spark and fuel. This is catastrophic engine damage if the valves and pistons collide. Inspect the timing belt visually for damage; you might need special tools or a mechanic to verify its timing.
3. Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the position of the crankshaft. A faulty CKP sensor prevents proper timing of the spark and fuel injection. This is a relatively common failure point and easy enough to check and replace.
4. Cam Position Sensor (CMP Sensor): Similar to the CKP sensor, but for the camshaft. A faulty CMP sensor can lead to similar problems.
5. Fuel Pressure Regulator: While you say you have fuel, ensure the fuel pressure is correct. A faulty regulator might deliver inadequate pressure at the injectors. You'll need a fuel pressure gauge to test this.
6. Ignition Coil(s): Although you mentioned spark, weak or intermittent spark might be the issue. A multimeter can test the coil output.
7. Ignition Control Module (ICM): The ICM controls the ignition coil(s). A faulty ICM can cause intermittent or complete spark failure.
8. Airflow Sensor (MAF Sensor): A faulty MAF sensor can provide inaccurate data to the engine computer, leading to poor fuel mixture and a no-start condition.
9. Computer (ECM): Though less likely, a failing Engine Control Module can cause unpredictable issues. This is usually a last resort after other possibilities are ruled out. Diagnosing ECM issues often requires professional tools and expertise.
Before you start:
* Check the basics: Ensure the battery is fully charged and the battery cables are clean and tight. A weak battery can prevent the starter from cranking sufficiently, even if you have spark and fuel.
* Listen carefully: When cranking, does the engine sound normal? A strange noise (e.g., knocking, rattling) might indicate a more serious internal problem.
Recommendation: Start with the compression test. If the compression is low, you'll need to investigate further to determine the underlying cause. If compression is good, move on to checking the crankshaft position sensor, then the camshaft position sensor, fuel pressure, and ignition system components. If you're not comfortable working on the vehicle yourself, a qualified mechanic is the best option, especially if you suspect timing-related problems.
