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clanking/knocking and misfire after spark plug change

1K views 11 replies 5 participants last post by  SwampDaddy 
#1 ·
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 company’s 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 didn’t 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 I’m 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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#3 ·
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...
 
#5 ·
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.
 
#8 ·
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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#9 ·
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.
 
#11 ·
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 don't have the space or tools to pull the engine, so it was incredibly stressful to potentially see my beloved Wrangler die. I'm an avid mechanic, and I'll try not to be a stranger; thanks for all your help.
 
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