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Old 11-19-2013, 03:58 PM   #1
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Exclamation Spark Plug problem :/

Hey forum!
So last night change my spark plugs in my '98 TJ 4.0 because I thought it might help to acceleration. I replaced them with the Autolite AP985 single platinum's. Now its idling rough, like its shaking, not too bad, but it's noticeable. I don't recall my baby doing this before-hand so what could it be?

It's not misfiring, or stalling, or anything, it's just shaking bad at idle

You can check off:
-correct wiring ( i checked it with the diagram)
and
-gap (i gapped all the plugs to .35 in)

I'm relatively new to 4-wheeled vehicle engines so cut me some slack

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Old 11-19-2013, 04:01 PM   #2
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I'm not certain, but I was always told the standard copper plugs were best for these engines.

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Old 11-19-2013, 04:21 PM   #3
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^^^ I heard that same Rumor !

I'm sure YOU checked ALL VACUUM Lines being sure one didn't just happen to come loose or fall off it's Nipple ~~~~~~~~ RIGHT ┐
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Old 11-19-2013, 06:19 PM   #4
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Did you double check the wires to verify that they are securely attached to the plugs?
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Old 11-19-2013, 09:12 PM   #5
Knows a couple things...

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Quote:
Originally Posted by Reznor View Post
I'm not certain, but I was always told the standard copper plugs were best for these engines.
Whoever says that does not understand spark plug technology. They will often say that from having installed the wrong type of plugs & just go back to the stock plugs and then go on a mission to misinform the world that only standard copper plugs work properly.

The right platinum plugs perform well for 100k miles, the right iridium tipped plugs run well for upwards of 200k miles. Either will continue to fire in many conditions that would cause a conventional plug to misfire. And the right technology plugs depends on engine type, ignition type, and model year of engine. The right platinum plug for a 1997 4.0L engine, would not be the right platinum plug for the far more fussy 2000 and newer distributorless 4.0L engines.

CPRJeeper, that AP985 is the right plug and it works very (!) well in your model year and engine type. That misfiring you're experiencing can be from a broken plug, mis-gapped plug, bad ignition wire, miswired ignition wire, or maybe the distributor cap or rotor are not properly in place. I've been doing tunes in distributor equipped engines since the 60's and any of those can and do happen with even experienced mechanics. I'd just go over everything to find out what is causing the misfire... because it's not from the AP985 model plug you installed which is the correct model that performs very well.
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Old 11-19-2013, 10:35 PM   #6
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Quote:
Originally Posted by Jerry Bransford View Post

CPRJeeper, that AP985 is the right plug and it works very (!) well in your model year and engine type. That misfiring you're experiencing can be from a broken plug, mis-gapped plug, bad ignition wire, miswired ignition wire, or maybe the distributor cap or rotor are not properly in place. I've been doing tunes in distributor equipped engines since the 60's and any of those can and do happen with even experienced mechanics. I'd just go over everything to find out what is causing the misfire... because it's not from the AP985 model plug you installed which is the correct model that performs very well.
THANKS! Tomorrow is my day off and I will go over all of those things you mentioned, its not really like misfiring thing because it's accelerating excellently, its just a rough idle and shakes more than i noticed before hand, but i will check all of those things tomorrow and keep you all posted, but for tonight, I'm fishing!

P.S. I don't know if this means anything to the situation, but I did just have a new cat and muffler put on (professionally) that same morning.
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Old 11-19-2013, 11:22 PM   #7
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Thanks to Jerry B for his consistent and patient replies. I've heard Jerry on multiple occasions answer this same question about plugs for TJ's. He does so with the experience of a good teacher. It's good folks like Jerry B that make this forum what it is for the rest of us. Thanks again for hanging in there with those of us who are just beginning to experience the joys and challenges of Jeep ownership.

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