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Old 01-25-2010, 12:26 AM
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Question Engine knock and rough idle help

Hello everyone, ive been a lurker for awhile and have gotten some great advice reading the forum. I have a few noises comming from my tj that I can't figure out and was wondering if anyone could help me or has had similar problems.

First, I have noticed an engine knock that persists while idling until the engine warms up. It is not a clicking noise, but more of a solid 'knock' that is lower in pitch than the valves. It is slightly louder than the valves and when reving the engine it speeds up and becomes inaudible at around 2000rpm.

Second, I tried to fix this noise by replacing the spark plugs, but in the process created a new problem. Now my engine idles roughly until it is warmed up and the knock is still there. It shakes all over in the engine bay and intermittently bogs out a little bit. It's not that bad, but it did not do this at all before I changed the plugs. Also, a wierd thing, I don't think the plugs had ever been changed(has 97xxx miles on it), and the gap on the old plugs was like .09in. The plugs I put in I gapped to .035, would this have a significant effect on the engine?

Any advice on what to do next to try and diagnose these sounds would be greatly appreaciated!
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Old 01-25-2010, 12:57 AM   #2
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I'm not gonna be able to help you with the plug choices...but what plugs did you put in? Certain plugs don't run well in our engines. Might wanna run a search for recommended plugs and gaps.

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Old 01-25-2010, 07:43 AM   #3
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Champion Truck Plugs are recommended if you have a 4.0 direct coil setup. They should be gapped to .035.
Attleboro, MA
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Old 12-26-2010, 03:14 PM   #4
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I have the same "knock" noise at start up until my engine is warm. I have the 2.5 and just changed the plugs and wires but I don't have the rough idle. Did you double check the connections on the plugs, I found a few were difficult to get connected.
Cody G 2004 Rubi
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Old 12-26-2010, 03:37 PM   #5
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Yup - run a search - right under your hood. There's a label on the firewall that tells you what Jeep recommends because that's what they designed the head to use. It shows the brand, the number, and the gap.
It's no wonder the country is falling apart - stupidity abounds!
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Old 12-26-2010, 03:54 PM   #6
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anyone knows about the ticking sound when engine is running made by the vacuum regulator on the driver side behind the windshield washer bottle?

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