* Crankshaft Position Sensor (CKP) or Cam Position Sensor (CMP): These sensors tell the engine's computer the position of the crankshaft and camshaft. If they're faulty, the computer won't know when to fire the spark plugs correctly, even if there's spark. The timing might be off or completely absent, leading to a no-start condition. This is a very common cause of no-start issues even with fuel and spark.
* Cranking Speed: While you say it has fire, is the engine cranking *strongly*? If the battery is weak or the starter is failing, the engine might not be turning over fast enough to ignite the fuel-air mixture reliably. Check the battery voltage during cranking. It should be above 10 volts.
* Fuel Injectors: While you have fuel pressure, the injectors themselves might be clogged, sticking, or not receiving the signal to open. A fuel pressure gauge only tells you if there's pressure in the rail; it doesn't guarantee the injectors are spraying fuel. A noid light (or testing with a multimeter) on each injector wire can confirm they are receiving the signal to open.
* Computer/ECM Issues: A faulty Engine Control Module (ECM) can prevent the engine from starting, even with the correct signals from other sensors. This is less likely but possible.
* Ignition Control Module (ICM): This component is less common on newer vehicles, but older GM vehicles sometimes have this component. It controls the spark. It could be malfunctioning even if there is spark in some cylinders.
* Air Intake System: A severely restricted air intake system could prevent sufficient airflow to support combustion. Check for clogs in the air filter or damaged intake tubing.
* Security System: If the vehicle has a factory or aftermarket security system, it might be preventing the engine from starting.
Troubleshooting Steps:
1. Verify Cranking Speed: Have someone crank the engine while you check the battery voltage. It should remain above 10V during cranking. A slow crank suggests a weak battery, corroded battery terminals, faulty starter, or a bad connection somewhere.
2. Check for Spark at All Cylinders: Don't just assume there's spark. Use a spark tester to verify a strong spark at each spark plug wire. A weak spark can be insufficient to ignite the fuel.
3. Check Fuel Injector Pulse: Use a noid light or multimeter to confirm that each injector is receiving a pulse signal from the ECM.
4. Inspect the CKP and CMP Sensors: These sensors are prone to failure. They're usually relatively easy to access and relatively inexpensive to replace.
5. Scan the OBD-II Codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the ECM's memory. These codes can provide valuable clues about the problem.
If you're not comfortable working on vehicles, take it to a qualified mechanic. Trying to diagnose this issue without proper tools and knowledge could lead to further damage. The problems listed above are possible, but without testing, pinpointing the exact cause is difficult.
