This could be caused by several issues, ranging from relatively simple to more complex repairs. Here's a breakdown of potential causes, starting with the most common and easiest to check:
Likely Causes:
* Spark Plug: A fouled, damaged, or incorrectly gapped spark plug is the most frequent culprit. Inspect the spark plug for wear, fouling (black, oily, or white deposits), or damage. Replacing it is relatively inexpensive and easy.
* Ignition Coil (Coil Pack): The ignition coil for cylinder 5 might be failing. These coils often wear out over time and can cause misfires in the cylinder they serve. Testing the coil with a multimeter or replacing it is usually the next step.
* Worn or Damaged Spark Plug Wire: If your Tahoe uses individual spark plug wires (less common on some 5.7L engines, they often use coil-on-plug), a cracked, frayed, or poorly connected wire to cylinder 5 could prevent a spark.
* Injector: A clogged or faulty fuel injector in cylinder 5 prevents sufficient fuel from reaching the combustion chamber. This can be tested with a fuel pressure gauge and injector flow test.
Less Likely, but Possible Causes:
* Valve Problems: A burnt, bent, or sticking valve in cylinder 5 can interfere with combustion. This is a more involved repair requiring head work.
* Compression Issues: Low compression in cylinder 5 suggests a problem with the piston rings, valves, or head gasket. A compression test is necessary to diagnose this.
* Wiring Harness Issues: A damaged or shorted wire in the harness leading to the spark plug, coil, or injector could also be the problem.
* Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP): While less likely to cause a single cylinder misfire, a failing sensor can disrupt timing and lead to misfires.
Troubleshooting Steps:
1. Visually inspect: Start by inspecting the spark plug, wire (if applicable), and ignition coil for cylinder 5. Look for obvious signs of damage.
2. Check for codes: Use an OBD-II scanner to confirm the P0305 code and look for any other related codes.
3. Replace the spark plug: This is the cheapest and easiest fix, and often solves the problem.
4. Test the ignition coil: If replacing the spark plug doesn't work, test the coil for continuity and resistance. If faulty, replace it.
5. Check fuel injector: Test the fuel injector for proper operation.
6. Further diagnostics: If the above steps don't solve the problem, you'll likely need more advanced diagnostic tools and potentially professional help to diagnose issues like low compression, valve problems, or wiring harness issues.
Important Note: Always consult your vehicle's repair manual for specific instructions and procedures. Attempting repairs beyond your skill level can cause further damage. If you're not comfortable working on your vehicle, it's best to take it to a qualified mechanic.
