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Old 09-24-2012, 07:47 PM   #1
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Spark Plugs

I have a 2000 4.0 sport. I changed the plugs from standard copper champions to double platinum champion 7034s. It gets much better mileage now as the copper plugs were toast.

It runs great above idle but iis very rough at idle. Especially cold idle. Smooth as silk once you hit the gas though.

Any ideas? Does the spark rail ( may be wrong term) "snap" back on he plugs? It did not notice a " click" on any of the boots when connecting rail back to plugs.

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Old 09-25-2012, 09:21 AM   #2
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Old 09-25-2012, 02:15 PM   #3
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Any ideas guys?
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Old 09-25-2012, 03:21 PM   #4
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Whatever the issue is, those Champion 7034 spark plugs won't cause that problem if properly installed, properly gapped, and if all six boots on the coil rail made it over their respective spark plugs. A bad idle can be from a bad TPS (throttle position sensor), dirty IAC (idle air controller), pad 02 sensor, etc. but if those spark plugs were properly installed, I wouldn't worry about them. You didn't by any chance get any dielectric intended for the spark plug threads on their electrodes did you?
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Old 09-25-2012, 03:34 PM   #5
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I used a dab of copper anti seize on each plug but made certain I did not get near the electrodes. I did not use dielectric grease on the plug boots.

No idling problems before the plug change. I gapped to 0.035" before I installed. I did not torque the plugs but tightened sufficiently.

I do not think the plugs are the problem. Is there a way to seat the plug boots wrong, as in not push on far enough? I assume the bolts would pull everything together.
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Old 09-25-2012, 03:46 PM   #6
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I can guarantee it is possible to get one of the coil rail's plug boots so it's not over its spark plug when you tighten the bolts down. I managed to do that and didn't notice until I started the engine and it was running like crap. If yours are seated properly, and I don't doubt they are, perhaps there's an issue somewhere with one of the connections inside one of the boots.
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Old 09-25-2012, 04:24 PM   #7
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it is also possible when removing the wires you damaged them internally. ive seen it a lot, and even done it once before. its more common on wires that are very old and have been hot before ( run along near exhaust, intake, or other hard metal engine parts that get warm.) changing plug wires would be a good next step, provided that checking connections doesn't solve your problem.
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Old 09-25-2012, 04:50 PM   #8
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His 2000 4.0L is new enough that it uses a coil rail and no longer has ignition wires.
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Old 09-25-2012, 04:58 PM   #9
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my bad I forgot about those new fangled ignition. well then I'd check connections, if they are good, get a good obd2 scanner and read your computer at an idle. see which cylinder has the varying spark times or spikes in the pattern.
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Old 09-25-2012, 07:40 PM   #10
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Thanks everyone. I'll give it a good look tomorrow and make sure it's all buttoned up correctly. What would be the next step if everything is good? Just replace the coil rail? Not worry about it since after you hit the gas after initial start up its fairly smooth? Even after its warm at idle it is slightly rough. But under throttle, even light it runs great.
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Old 09-25-2012, 07:45 PM   #11
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Quote:
Originally Posted by WVU Mountainman View Post
Thanks everyone. I'll give it a good look tomorrow and make sure it's all buttoned up correctly. What would be the next step if everything is good? Just replace the coil rail? Not worry about it since after you hit the gas after initial start up its fairly smooth? Even after its warm at idle it is slightly rough. But under throttle, even light it runs great.
Re-read the suggestions already made in post #4 above. Especially about cleaning the IAC... then try replacing the TPS if cleaning the IAC with some aerosol throttle body cleaner doesn't cure it.

Cleaning the IAC well enough to restore it to operation can often be done without removing it. Just start the engine and feed some cleaner into the Idle Air Control Passage Inlet while keeping the RPMs up with the throttle control lever. The engine may die a few times while doing it but that's ok, just restart it. That will cause cleaner to get sucked in through the Idle Air Control Passage Inlet and clean its solenoid actuated plunger inside the meters air into the engine at idle. Let the RPMs idle as often as possible, that is the only time the cleaner will be sucked into the air passage inlet.
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Old 09-25-2012, 08:00 PM   #12
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Thanks Jerry. I'll try this soon.

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