Misfire/Rough Idle/Shaking - Mustang Evolution

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Old 03-19-2013, 01:00 PM   #1
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Misfire/Rough Idle/Shaking

So I had a thread insert installed a few days ago on #3 (spark blow out) Everything went smoothly on the install. Car starts up fine but now has a misfire on that same cylinder. Checked plug/cop and it seems to be fine.

Car cold starts and idles good until the idle comes down to 800 rpm then it starts to shake (very noticeable) and you can hear some sort of pop on the exhaust. Although the rpms stay at 800 somewhat consistent. It's hard to notice if it actually dips a little perhaps 50-100 rpms at the most. If you go above 1k you don't feel the misfire at all and drives fine. I am worried it might be a damaged cylinder but that's beyond my mechanic skills. So I might be looking at some $$$$$ repairs

I might try to get a video later on.


02 GT
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Old 03-19-2013, 01:07 PM   #2
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When in doubt, replace the cop and check your gap.
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Old 03-19-2013, 01:37 PM   #3
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Does the exhaust make a sort of glubbing sound? Or is it more of like a back-fire popping sound? I know that my car mildy shakes at warm idle but i dont notice any missfiring.
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Old 03-19-2013, 01:39 PM   #4
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+1 I think mustang's are just known for a alight shake at warm idle mine does it and everyone I have ever known that had a stang has a slight shake. It may sound stupid bit make sure the thread insert is on there good and the plug is in the cyl tight it may have backed out just a little bit just enough to not fire right.
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Old 03-19-2013, 01:45 PM   #5
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Quote:
Originally Posted by GReese87 View Post
+1 I think mustang's are just known for a alight shake at warm idle mine does it and everyone I have ever known that had a stang has a slight shake. It may sound stupid bit make sure the thread insert is on there good and the plug is in the cyl tight it may have backed out just a little bit just enough to not fire right.
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Old 03-19-2013, 01:53 PM   #6
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Quote:
Originally Posted by Mustang936 View Post
Does the exhaust make a sort of glubbing sound? Or is it more of like a back-fire popping sound? I know that my car mildy shakes at warm idle but i dont notice any missfiring.
It's back fire popping sound. I've already made sure everything is tight and neat. This is a noticeable shake, it didn't use to shake at all before.
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Old 03-19-2013, 01:56 PM   #7
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I have no clue what to tell you man, i hope someone else on here has an answer for you.
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Old 03-19-2013, 02:13 PM   #8
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The injector may have been damaged pull it and swap with another cylinder
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Old 03-19-2013, 04:50 PM   #9
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Damn it took forever to load the video.

You can tell it start to shake around the 17 second mark.


and yes it's more like a gubbling sound at idle
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Old 03-19-2013, 07:11 PM   #10
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Well since you have the check engine light on take it to a auto parts store and have them read the code first then get bacteria to us on that.
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Old 03-20-2013, 12:43 PM   #11
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Mine glubs but its a very different glubbing sound than that, I'd say go get the codes run at an auto-parts store.
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Old 03-20-2013, 01:49 PM   #12
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I also had a plug blow out. Mine before the blow out had a misfire that popped/ backfire but it was only at idle he said.
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Old 03-20-2013, 01:59 PM   #13
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did you make sure to use tune up grease on the coil pack inside ? have seen it throw codes if you dont
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Old 03-20-2013, 04:33 PM   #14
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P303 cylinder misfire. Going to mess with it over the weekend. We shall see what the problem
Is
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Old 04-08-2013, 04:51 PM   #15
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Update:

Well some good and bad news

It seems I think I know what the problem is. After I got the new spark plug installed and tighten everything down, the car ran and idled flawlessly for about 15 minutes. The it started to misfire again and i can hear a slight tick around the #3 cylinder. I am assuming this tick is related to the spark plug as I had a similar but a lil bit louder tick before i had the blow out.

This is what I think is happening. New plug and tighten everything down. The problem is I believe i have compression leak through the Insert! This is causing compression to also leak out through the plugs and in the process making the plug back out or something causing a misfire. It also explains why the car ran flawlessly for a few minutes until the leaking compression took its toll.

What do you guys think? It sucks that I am busy with school and work. I'll see what I can do on the weekend. I am gonna attempt to see if i can get the insert out and try a new one.

Worst case scenario, I'll have to remove the passenger side head. Has anyone remove the head with the engine in the car?
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