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Discussion Starter · #1 ·
Hello all, I have a 2003 Mustang 3.8 V6, auto, basic Mustang with 122,000 trouble free miles. Well driving on Sunday the engine started to run very rough and a knocking sound can be heard. Had it towed to my house.

The oil level, coolant and all fluids are good to go. Check engine light showed P0340 code. I replaced the camshaft postion sensor and cleaned the idle air control valve. Still have the engine barley able to run and a knocking sound.

Unplugged the ignition and engine turns over very freely and no noise. I removed all the spark plugs and valve covers. Everything still looked good. I'm hoping it's not a rod or bearings, I'm looking for "other" possible causes before writing off the car. My next step is to do a compression test but looking for ideas...

Thanks,
 

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No water in the oil, engine turns over freely with no noise, are all good signs. I would check further before replacing the engine. You are on the right track, a compression test will tell. Good luck. The CEC code is an EGR problem. Check the EGR system for carbon build up.
 

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Discussion Starter · #3 · (Edited)
Well I performed a compression test and found #6 cylinder at 120 psi and falling. Did it twice to confirm. I thought a bad lifter or bent pushrods. I removed everything, got all the lifters out, rods, rocker arms, etc.. out all good. Nothing remotely wrong. Even removed the the camshaft synchronizer, all good and spotless. Camshaft lobs all good. Now what, no idea where or what to do next. I find it extremely hard to believe that a rod or spun bearing can happen for no reason. Any smart folks out there that have any ideas...? I'm at a stopping point now.
 
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