# '98 Jeep Grand Cherokee Suddenly misfiring

**URL:** <https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288>\
**Category:** Maintenance/Repairs\
**Tags:** jeep\
**Created:** [July 16, 2011, 1:16pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288 "2011-07-16T13:16:20Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jroush](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jroush](https://community.cartalk.com/u/jroush)\
**Post date:** [July 16, 2011, 1:16pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288/1 "2011-07-16T13:16:20Z")

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Hi all,

I was driving my '98 Jeep Grand Cherokee Laredo (6cyl 4.0l 4 wheel drive) on the freeway when it, very suddenly, started shuddering badly. The check engine light came on and then started blinking. I pulled right over and shut it off. I stared it back up and the engine is misfiring badly. I had a code reader with me and it’s showing three codes. A random misfire, a cyl #5 misfire, and a Cyl#6 misfire. It will sit and idle (very roughly obviously).

There was no drop in RPMs, oil pressure, voltage or anything when it happened.

I got it home and replaced the distributor cap/rotor, all six spark plugs, and the plug wires but there is no improvement. I cleared the Codes and re-read them and got the same errors again.

Any suggestions from those wiser than I (that’s pretty much all of you here) on what it might be or what to check next?

Thanks, Jeff

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**Author:** ![nevadawrench](https://avatars.discourse-cdn.com/v4/letter/n/f1d935/32.png) [@nevadawrench](https://community.cartalk.com/u/nevadawrench)\
**Post date:** [July 16, 2011, 2:20pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288/2 "2011-07-16T14:20:51Z")

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Check compression. I wouldn’t be suprised if you had a blown head gasket between cylinders 5 & 6. If you don’t have a compression tester, it’ll cost about $20.

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**Author:** ![jroush](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jroush](https://community.cartalk.com/u/jroush)\
**Post date:** [July 16, 2011, 2:39pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288/3 "2011-07-16T14:39:41Z")

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I think I do have a compression tester around someplace. I’ll add that to the list of things to check. Thanks!

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**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\
**Post date:** [July 16, 2011, 3:48pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288/4 "2011-07-16T15:48:00Z")

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To have the trouble happen so quickly I would guess the trouble is due to either a fuel problem or a valve timing issue. I’m not sure if this engine uses a timing belt or chain. If the compression numbers show up low I would check the valve timing.

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**Author:** ![jroush](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jroush](https://community.cartalk.com/u/jroush)\
**Post date:** [July 23, 2011, 5:03pm UTC](https://community.cartalk.com/t/98-jeep-grand-cherokee-suddenly-misfiring/66288/5 "2011-07-23T17:03:13Z")

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Followup: Cylinder #5 indeed had no compression so, sounding like something way above my DIY repairs paygrade, off to the experts it went. Turns out it had a broken valve spring on #5. The misfire code on #6 was simply a ghost. I had the spring replaced and it runs better now than it has since I’ve owned it.

Thanks to the CT community once again for all your help.

Jeff