* Timing: The most likely culprit after a head gasket replacement is incorrect timing. The timing belt (or chain, depending on the year) might be a tooth or more off, rendering the engine unable to fire properly. Verify the timing marks meticulously using a reliable workshop manual. This is crucial.
* Camshaft Position Sensor (CMP sensor) or Crankshaft Position Sensor (CKP sensor): These sensors tell the computer the engine's rotational position. A faulty sensor will prevent proper fuel delivery and ignition timing. Check the sensor connectors for corrosion or damage. A scan tool can often detect CMP/CKP sensor problems.
* Ignition System Issues: While you mentioned spark, the spark *strength* might be insufficient. Weak spark plugs, failing ignition coil(s), or a faulty ignition control module can prevent reliable combustion. Test the spark with an inline spark tester for strength.
* Fuel Delivery Problems: Although you say you have fuel, verify fuel *pressure*. A weak fuel pump, clogged fuel filter, or faulty fuel pressure regulator can prevent sufficient fuel from reaching the injectors. A fuel pressure gauge is needed to check this.
* Vacuum Leaks: A significant vacuum leak can disrupt the air/fuel mixture, preventing proper combustion. Inspect all vacuum lines and connections carefully for cracks, disconnections, or loose clamps, especially those near the intake manifold and throttle body.
* Wiring Issues: During the head gasket replacement, it's possible that a wire was damaged or improperly reconnected. Carefully examine all wiring harnesses and connectors, looking for broken wires, loose connections, or corrosion.
* Incorrect Head Bolt Torque: If the head bolts weren't torqued to the manufacturer's specifications, the head could still be warped, even if it was resurfaced. This could cause leaks and affect compression.
* Interference during reassembly: Something may have been installed incorrectly (like a valve timing component) resulting in valve interference.
Troubleshooting Steps:
1. Verify Timing: This is the top priority. Consult a repair manual for your specific engine year.
2. Check Fuel Pressure: Use a fuel pressure gauge.
3. Inspect the spark: Use an inline tester. Don't just rely on visually seeing a spark.
4. Scan for trouble codes: Use an OBD-II scanner to check for any diagnostic trouble codes (DTCs).
5. Check Vacuum: Carefully inspect all vacuum lines.
6. Inspect Wiring: Look for any damage or loose connections.
If you're not experienced with automotive repair, it's highly recommended that you take the vehicle to a qualified mechanic. Incorrectly timed engines can cause significant internal damage. This systematic approach should help you diagnose the problem, but professional assistance may be necessary.
