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Tiny
HANK123
  • MEMBER
  • 2003 JEEP WRANGLER
  • 4WD
  • AUTOMATIC
  • 25,469 MILES
2003 jeep wrangler we changed sparks plugs and coil pack and crakshaft sesor still has a miss
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Friday, July 15th, 2011 AT 7:44 PM

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Tiny
CARADIODOC
  • EXPERT
Has the Check Engine light turned on? If so, there should be a fault code indicating which cylinder is misfiring. Switch the injector with one from a different cylinder to see if the code changes to that other cylinder. Chrysler has extremely little trouble with injectors, but if you already changed the ignition parts, that just leaves fuel and compression.
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Friday, July 15th, 2011 AT 7:56 PM
Tiny
HANK123
  • MEMBER
It runs ok until you drive it alittle ways until it gets hot then it will satat missing
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Friday, July 15th, 2011 AT 8:01 PM
Tiny
CARADIODOC
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Misfires should be detected by the Engine Computer and that should turn on the Check Engine light. Regardless, you may want to see if there are any diagnostic fault codes set in the computer that will identify which cylinder is causing the misfire. Many auto parts stores will read the codes for you for free.

Did you use a spacer to set the critical air gap for the new crank sensor? It should have had either a thick paper spacer on the end or a thin plastic rib molded onto it.
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Friday, July 15th, 2011 AT 8:15 PM
Tiny
HANK123
  • MEMBER
It had a code at first said coil pack after we put
everthing in we cleared codes after we drove it scan it shows no codes we did not put a spacer between crakshaft sensor the jeep old crankshaft sensor did not have one either
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Friday, July 15th, 2011 AT 8:27 PM
Tiny
CARADIODOC
  • EXPERT
Put some punctuation in your replies so I don't misinterpret your meaning. It appears you're not getting any codes now with the new coil pack.

The old sensor won't have a spacer. It slides off as soon as the engine is started. If you reinstall an old aftermarket style sensor, you're supposed to cut the remaining part of its plastic rib off and use a new paper spacer from the dealer.

Did the previous code actually specify the coil or did it just refer to a misfire? If it was for the coil, you have to read that as the coil circuit which includes the wiring to it. The computer can only detect an open or shorted condition which can be caused by the wiring to the coil as well as the coil itself. In particular, look for any electrical connectors that could have corrosion in the terminals.

If the code was specific to a certain cylinder, think about switching injectors and performing a compression test. Loss of compression would be my last guess because it runs okay when it's still cold.

The next thing would be to visit a mechanic with a scanner that can read live sensor data while driving. Look at the "AIS Steps" which is the number of steps the computer has commanded the automatic idle speed motor to for proper idle speed. Normal is typically around step 32. When a single cylinder misfires, expect to see around step 50 or higher.

The oxygen sensor readings can provide some clues too. If one bank is staying lean longer than normal, suspect a blocked injector on that side of the engine. Fuel trim numbers will also be high positive for that side. A severely plugged air filter can increase manifold vacuum which is detected by the MAP sensor and will be interpreted as reduced load on the engine. The computer will respond by commanding less fuel which can lead to a lean misfire. That will usually show up as a "random cylinder misfire" code.
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Friday, July 15th, 2011 AT 8:54 PM

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