# Jeep misfries after tuneup

**URL:** <https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312>\
**Category:** Maintenance/Repairs\
**Created:** [May 11, 2009, 2:39pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312 "2009-05-11T14:39:57Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![jeep98](https://avatars.discourse-cdn.com/v4/letter/j/8edcca/32.png) [@jeep98](https://community.cartalk.com/u/jeep98)\
**Post date:** [May 11, 2009, 2:39pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/1 "2009-05-11T14:39:57Z")

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I have a 98 jeep with a straight 6.  
  
 Cylinder 1 misfires, I installed all new spark plugs, a new cap, new plug wires, and a new fuel injector for cylinder one.  
  
 What else is the problem? If I do a compression test what is that going to tell me, rebuild the engine?  
  
  
  
 Thanks

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**Author:** ![Xebadaih](https://avatars.discourse-cdn.com/v4/letter/x/d07c76/32.png) [@Xebadaih](https://community.cartalk.com/u/Xebadaih)\
**Post date:** [May 11, 2009, 4:11pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/2 "2009-05-11T16:11:37Z")

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Do a compression test on all cylinders. If #1 is low, put a little motor oil in it through the spark plug hole. Redo the test and if the compression is higher after adding the oil it is likely your rings. If the oil doesn’t change anything, it is likely a valve issue.

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**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\
**Post date:** [May 11, 2009, 5:29pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/3 "2009-05-11T17:29:36Z")

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Did the wires get attached to the right plugs? Are they properly attached or maybe one could be loose?

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**Author:** ![jeep98](https://avatars.discourse-cdn.com/v4/letter/j/8edcca/32.png) [@jeep98](https://community.cartalk.com/u/jeep98)\
**Post date:** [May 20, 2009, 1:17pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/4 "2009-05-20T13:17:36Z")

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Checked all the wires and plug everything is good.

In theory, the spark plug would have oil on it if the rings are bad.  
If the values are bad it back fire.

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**Author:** ![UncleTurbo](https://avatars.discourse-cdn.com/v4/letter/u/e9a140/32.png) [@UncleTurbo](https://community.cartalk.com/u/UncleTurbo)\
**Post date:** [May 20, 2009, 1:22pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/5 "2009-05-20T13:22:31Z")

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If you haven’t already done so, switch the number 1 plug with a plug in another cylinder, to rule out a defective plug. Was the Jeep running fine prior to the tune up?

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**Author:** ![Manolito](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/manolito/32/3070_2.png) [@Manolito](https://community.cartalk.com/u/Manolito)\
**Post date:** [May 20, 2009, 1:43pm UTC](https://community.cartalk.com/t/jeep-misfries-after-tuneup/30312/6 "2009-05-20T13:43:02Z")

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I don’t know what your engine uses for a crank pat osition sensor, or where it is located, but take a good look at the sensor and the tooth on the reluctor that corresponds to #1 cylinder. If that tooth is broken or there is a sharp edge on the reluctor near that tooth, it will cause a misfire. Also examine the electrical lead to the sensor. Failing insulation/shielding can cause electrical interference to get in to the sensor lead, causing a misfire.