* Cranking speed: Is the engine cranking *fast* enough? A slow crank can prevent the engine from starting even with fuel and spark. Check the battery voltage and connections. A weak battery or bad connection will cause slow cranking. Consider testing the starter motor itself.
* Fuel pressure: While the pump primes, that doesn't guarantee sufficient fuel *pressure* at the fuel rail. You need a fuel pressure gauge to measure this. Low fuel pressure, even with the pump running, will prevent starting. A clogged fuel filter is a common cause.
* Fuel delivery: Even with adequate pressure, there could be a problem with injectors not spraying fuel properly. A clogged injector or a faulty injector control module (or PCM issue affecting injector control) could be the culprit.
* Crankshaft Position Sensor (CKP): A faulty CKP sensor won't allow the computer to properly time the spark and fuel injection. The engine will crank but not start. This is a common issue on these trucks.
* Cam Position Sensor (CMP): Similar to the CKP sensor, a faulty CMP sensor can prevent proper engine timing.
* Ignition control module (ICM): Although you mentioned spark, a weak or failing ICM could provide insufficient spark for reliable starting.
* Airflow sensor (MAF) or Throttle Position Sensor (TPS): A faulty sensor may send incorrect information to the computer preventing proper fuel/air mixture. This is less likely given that it cranks and the fuel pump primes.
Troubleshooting Steps:
1. Battery Voltage: Check the battery voltage while cranking. It should be above 10 volts. Low voltage points to a weak battery, bad connections, or a failing alternator.
2. Fuel Pressure Test: This is crucial. Rent or borrow a fuel pressure gauge and connect it to the fuel rail to measure pressure while cranking. The specification should be in your repair manual (or online).
3. Check Spark Strength: While you've confirmed spark, ensure it's strong enough. A weak spark may not be sufficient to ignite the fuel-air mixture consistently.
4. Inspect Fuel Filter: A clogged fuel filter restricts fuel flow and should be replaced if it appears dirty or damaged.
5. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored trouble codes. These codes can point directly to the problem.
6. CKP and CMP Sensors: If the fuel pressure is good and you have a good spark, these sensors are prime suspects. They're relatively inexpensive to replace.
7. Professional Diagnosis: If you're not comfortable with these checks, take it to a mechanic. They have the tools and experience to diagnose the problem efficiently.
Without a fuel pressure test, it's difficult to pinpoint the exact cause. Start with the battery voltage and fuel pressure tests; they're the most likely culprits based on your description.
