Misfire Troubleshooting: The Tutorials

There are quite a few things that can cause a ‘dead’ cylinder. The next step is to check for the three basic things the cylinder needs to function, which are 1.) Spark, 2.) Fuel, 3.) Air.

To further help you along, in your troubleshooting, here are some more specifics:

  1. Ignition system problem. For example:
    1. Bad distributor cap (distributor equipped Jeeps).
    2. Bad coil-on-plug ignition coil (COP ignition system equipped Jeeps).
    3. Bad spark plug wire.
    4. Bad spark plug.
    5. Engine oil leaking onto the spark plugs from the valve cover.
  2. Fuel system problem. For example:
    1. Bad fuel injector.
    2. Fuel injector not being activated by PCM or due to a short in the wiring.
  3. Engine mechanical. For example:
    1. Low engine compression.

The above list may seem like troubleshooting a ‘dead’ (misfiring) cylinders is hard but with a good diagnostic strategy, you'll be able to find the root cause of the misfire.

Here are my suggestions (and the diagnostic strategy I use):

  1. Test the ignition system first.
    1. The Ignition System is usually the culprit behind most of the misfire (‘dead’ cylinder) conditions.
  2. Test the fuel injectors second.
    1. After eliminating the ignition system as the cause of the misfire, the next step is to make sure that the fuel injector is not fried internally.
    2. You can find an in-depth tutorial on how to do a fuel injector resistance test here: How To Troubleshoot A Bad Fuel Injector (Jeep 4.0L).
  3. Test the engine compression third.
    1. After making sure that the ignition system is providing Spark and the fuel injector is injecting fuel into the ‘dead’ cylinder, the next step would be to check that cylinder's compression.
    2. You can find an in-depth tutorial on how to test the ignition coil packs and spark plug wires here: How To Test Engine Compression (Jeep 4.0L).

The above list of tests can be modified to suit your particular diagnostic, troubleshooting needs (since there really isn't a specific cookie cutter way of diagnosing a car).

More 4.0L Jeep Diagnostic Tutorials

You can find a complete list of tutorials here: Jeep 4.0L Index Of Articles. Below, is a sample of articles you'll find in this index of articles:

  1. How To Test TPS Codes: P0121, P0122, P0123 (1997-2001 Jeep 4.0L).
  2. How To Test The MAP Sensor (1997-2003 Jeep 4.0L).
  3. How To Test Engine Compression (Jeep 4.0L).
  4. How To Troubleshoot A Bad Fuel Injector (Jeep 4.0L).
  5. How To Test The Crankshaft Position Sensor (1994-1996 4.0L Jeep).
  6. How To Bench Test A Starter Motor (Step By Step) (at: easyautodiagnostics.com).
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Jeep Vehicles:

  • Cherokee 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
  • Comanche 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992
  • Grand Cherokee 4.0L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

Jeep Vehicles:

  • Wagoneer 4.0L
    • 1987, 1988, 1989, 1990
  • Wrangler 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006