clanking/knocking and misfire after spark plug change - JeepForum.com
 
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post #1 of 12 Old 07-26-2021, 08:15 AM Thread Starter
KevinTJ2000
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clanking/knocking and misfire after spark plug change

Installed new Champion 7034 plugs and there was an immediate loud metal on metal knock on start up followed by low level clanking, and within a few seconds it was misfiring. I inspected and reinstalled the plugs and it did the exact same thing on start-up; it did this twice in a row after installing the new plugs with identical failure characteristics. I verified the plug cable routing and confirmed the pistons are all still connected and moving freely when manual hand cranking. My insurance companyís OBD2 dongle is not reporting a fault code.

Last summer I had my first overheat and replaced the entire cooling system along with many other wear-out items preemptively. I was thinking my next step would be to camera endoscope the spark plug holes to see if a piston is cracked. I was sure I made a mistake with the spark plugs until I inspected and confirmed the plugs are undamaged. I did not look closely for debris around the sparkplug before removing them, but I didnít notice any interference hand fitting the sparkplug socket either. Also, the cables are new as of last year, but there is a small split in the insulator jacket end shroud. An electrical gremlin from the cable damage/shorting could be causing chaos in the timing, and what Iím hearing could be the valves knocking as the engine controller then tries to compensate the timing and resulting misfire. I had the distributor tower one tooth off many years ago, and it seems like this could (hopefully) be a timing issue based on how the engine will start and run for 20-30 seconds and then start misfiring.

I'm the original owner of the 2000 2.5l TJ with 183K, and I've done all the maintenance myself. I had everything fixed except for the rear transmission seal, which I was saving for the first clutch replacement. I was thinking I had ten more years of life in the Jeep until this, yikes.

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post #2 of 12 Old 07-26-2021, 08:36 AM
jtec
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IIRC -
7034 is wrong plug - platinum is not recommended.
RC12ECC is suggested a solid core. And less expensive

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 12 Old 07-26-2021, 01:02 PM Thread Starter
KevinTJ2000
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I replaced the spark plug cables and it can idle with some minor clanking, but I can't increase the RPMs very much without the engine shaking and misfiring with periodic metal on metal banging sounds. My new general grabber tires may have thrown a stone in the spark plug well and entered the plug hole during plug repacement, or the misfire from the damaged cable was enough to fracture the already cracked piston. Now the fun begins...
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post #4 of 12 Old 07-26-2021, 01:06 PM Thread Starter
KevinTJ2000
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I understand, thanks. I have 80k on the 7034, and it appears my problem is much bigger than a sub-optimal sparkplug.
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post #5 of 12 Old 07-26-2021, 01:54 PM Thread Starter
KevinTJ2000
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I got to spend some time on the phone with local Jeep dealer service dept, and they don't suspect a cracked piston or debris entering the plug hole during replacement. The engine controller will fix the misfire at higher RPMs when I let it idle, and then it idles like normal for several minutes. The dealer suspects a valvetrain issue, but this would suprise me since I used mobil one from day one. It seems like the next step is ordering a camera to inspect the cylinders; at least now I know the cylinders aren't washed down with unburnt fuel.
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post #6 of 12 Old 07-26-2021, 02:15 PM
Fourtrail
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First thing I would do is put the old plugs back in and see if the problem persists. Wouldn't be the first time I have seen bad champion plugs out of the box.

80 CJ-5, 74 CJ-6, 56 CJ-5
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post #7 of 12 Old 07-26-2021, 03:16 PM Thread Starter
KevinTJ2000
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Quote:
Originally Posted by Fourtrail View Post
First thing I would do is put the old plugs back in and see if the problem persists. Wouldn't be the first time I have seen bad champion plugs out of the box.
Thanks, I'm going to try this. I dropped the old plugs from height into a metal can, but I retrieved them. The plug box was damaged and oreillys auto parts has agreed to take them back in the morning. I'll install new plugs tomorrow as the optimal next step.
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post #8 of 12 Old 07-26-2021, 04:06 PM
jtec
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some thoughts - easy free.
how would the tires throw a stone into cylinder, the engine is OFF during change. IDK
WITH ALL plugs removed is there any change in sound when cranking?

Attached if firing order - an easy check
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 12 Old 07-26-2021, 05:51 PM Thread Starter
KevinTJ2000
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The general grabber tires are notable for picking up rocks, but I think this is an unlikely root cause. The initial bang on start-up after plug replacement had me thinking something could have gone inside, however I always hand-fit the spark plug socket and I didn't hear anything fall inside. Something falling inside is the worst case; I'm hopeful it's a defective plug. A misfire could have initiated something more serious, but as long as the pistons are attached I think I can fix it with the engine installed. The engine hand cranks (with plugs removed) smoothly with compression at single plug installations and no unusual sounds. I've double checked the cable firing order routing, and the engine does idle on all four cylinders.
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post #10 of 12 Old 07-26-2021, 06:27 PM
Jeepsr4me
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You can mix up the plug wires and that 2.5 will run,. It will not run good but it will run. Look at the wires and put your hand on from cap to plug.
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post #11 of 12 Old 07-27-2021, 11:04 AM Thread Starter
KevinTJ2000
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KevinTJ2000

The root cause was confirmed to be defective Champion 7034 spark plugs I purchased from O'Reilly Auto Parts (5220 15th Ave NW, Seattle, WA 98107). The box had significant crushing damage, and I should have known not to install them.

This is a first for me, and the effects of faulty/damaged spark plugs were not what I would have expected. I donít have the space or tools to pull the engine, so it was incredibly stressful to potentially see my beloved Wrangler die. Iím an avid mechanic, and Iíll try not to be a stranger; thanks for all your help.
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post #12 of 12 Old 07-28-2021, 07:26 AM
SwampDaddy
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That’s great that it was a simple and cheap fix.
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