Here are some possibilities:
* Incorrect Spark Plug Gap: The most likely culprit. If the gap on your new spark plugs is incorrect (too wide or too narrow), it can lead to detonation (knocking). Double-check the gap with a feeler gauge and ensure it matches the manufacturer's specifications for your engine.
* Incorrect Spark Plug Type: You may have installed the wrong type of spark plug (heat range, reach, etc.). This can also cause detonation. Verify that the plugs you installed are the exact type specified in your owner's manual or a reliable online parts source for your specific Jeep Wrangler's engine.
* Loose Spark Plug: A spark plug that isn't fully tightened can cause a misfire and potentially a knocking sound. Check that all plugs are securely tightened to the manufacturer's specified torque. Using a torque wrench is essential to prevent over-tightening and damaging the threads.
* Damaged Piston or Connecting Rod: While less likely if the knocking started *immediately* after the spark plug change, it's possible that pre-existing damage was exacerbated by a misfire caused by an incorrectly installed plug. This is a serious issue requiring professional attention.
* Other Engine Issues: The spark plug change might have uncovered a pre-existing problem unrelated to the plugs themselves. Things like low engine oil, damaged bearings, or issues with the ignition system could all contribute to a knocking sound.
What to do:
1. Immediately stop driving the Jeep. Continued driving could cause significant engine damage.
2. Recheck your work: Verify that all spark plugs are the correct type, have the correct gap, and are properly tightened to the correct torque specification.
3. Check the engine oil level: Low oil pressure can cause knocking.
4. Listen carefully to the knock: Does it change with engine speed? Does it seem to be coming from a specific location in the engine? This information can help a mechanic diagnose the problem.
5. Consult a mechanic: If you've checked everything and the knocking persists, take your Jeep to a qualified mechanic for diagnosis and repair. Ignoring the problem could lead to expensive repairs.
The knocking is a serious warning sign. Addressing it promptly will save you time, money, and potential engine damage.
