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Discussion Starter #1 (Edited)
Ok guys having a weird issue here.. On acceleration or bump the trottle in neutral i can hear a rattling type sound. It doesnt get louder with rpms, if i unplug the #3 injector on the drivers side and rev, the rattling/tapping stops, and sounds like it should.. I pulled the plugs they look good, swapped injectors around and it still does it on that one cylinder... It almost spounds like a spun bearing but i dont think thats the issue, or hope it isnt anyhow. Whats ur thoughts?


Edit: just unplugged the coil pack for that cylinder, rev, no noise.. So no fire in that cylinder = no noise.. Perfect sound motor :(
Plug it back up, rev, rattle sound came back
 

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That means something in the bottom end is bad. It could be a rod bearing worn out, or maybe a bad wrist pin. Either way, time to pull the motor apart.
 

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Can you take a audio/video for us? Does sound like something like Mikey said although I've never heard a bad wrist pin. I've heard bad rod bearings and broken skirt causing piston slap several times though!
 

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yeah, sounds like something is loose in the rod on that cyl. without it dumping fuel its not firing and without the downward force it isn't knocking.
 

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Discussion Starter #5 (Edited)
Yeah ill do a video in a bit

I cant pick up the sound on my phone

& mikey thats what it sounds like to me too.
 

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Discussion Starter #7
so you have already exhausted all possibilities of this being a valvetrain issue? Who/when was this engine built and when did this noise show up?
Well, i was hoping for that issue other then a rod bearing lol Tappets went bad for the valves on that cylinder perhaps??
 

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A valvetrain issue would not go away when the cylinder is deactivated. That can only be a bottom end issue.
 

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A valvetrain issue would not go away when the cylinder is deactivated. That can only be a bottom end issue.
I agree with you for the most part. I was thinking a long-shot with a valve not seating properly under combustion pressure. Highly unlikely, I know, but with out compression test numbers at this point there's a 0.0001% chance it may not be bottom end related.

cobra R thunderbird, there are no tappets in a modular engine. Do a compression test if you have one available. If anything it will confirm that it is indeed a bottom end problem.

again: Who/when was this engine built and when did this noise show up? ?
 

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Discussion Starter #10
Its the one i built last year.
*lash adjusters is what i meant. Not tappets

The noise showed up after i raced it one nite. I may have over revved in my 1-2 shift. Not certain because i wasnt watching my rpms.. Too busy keeping the car on the pavement lol
 
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