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420A Mysterious vibrations

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Zero6391

Proven Member
263
38
Apr 10, 2014
Roswell, New_Mexico
Hello, so its been awhile since ive posted on here and its mostly cuz ive been stuck figuring out this problem. So at idle the engine shakes and u can feel the vibrations thru out the rpm range just not badly, the only time u really notice is at idle at 1k rpm. The problem started one day when i passed at semi at 120mph on the freeway and it was only for like a min then cruised at 80 mph well when i got to the next town thats when i noticed this shaking. So thought i spun a rod but when i pulled the pan everything was fine and there was no metal flakes, checked timing and its fine, i checked fuel pressure holds at 50 psi, i checked compression and it was 160 across all cylinders dry tested, all spark plugs are firing, fuel injectors are opening and closing and im not throwing a cel code. The motor mounts were all replaced recently and still look good. I do get detonation evidence on the spark plugs but again im not throwing a cel, front o2 sensor was replaced as it went out and the manifold had leaks so i had that and downpipe replaced with stainless steel piping, vacuum checks out at -20hg, swapped ECU, Crank, and Cam sensor but still no fix. Been like this since february hoping a cel would get thrown but still nothing, car isnt smoking either..... soo what do u guys make of it??? Cuz im lost on this LOL
 
Ive checked the pulley and it seemed to be in good shape externally and while the engine is running it isnt visually wobbling. When i look at the engine tho it almost seem like the vibration are on the transmission side. If it is the harmonic balancer would it cause the detonation in the cylinders?
 
I can say from personal experience that I purchased a 1g (4G63 - 7 bolt) with a flex plate that cracked, leading to the torque converter making contact with the bolts on the block and shaving metal from the converter case. It got out of balance enough to strip the TQ converter bolts.
 
Dude that sounds gnarly but i looked in there and there wasnt anything out of the ordinary. And i read somewhere about the flywheel bolts but i used red loctite on them so they are on there practicallt permanently... ive heard things about using red on them making it almost impossible to pull them off even with an impact. Ive checkes the egr valve and the tube and it all looked fine there
 
How bad are the signs of detonation? Just keep in mind that although detonation is a bad thing if left unchecked, the 420a shouldn't be nearly as sensitive to it as a 4g63. I say you should test the vibration. Since it happens at idle, leave it in neutral and rev it up a little to see if the vibration changes frequency. If it does, the problem lies in your engine, if no change, it may lie in your transmission.
 
Depends on how hard i drive the car LOL if i ease the car everywhere staying about 35% throttle there is almost no signs of detonation but if i floor it everywhere then it starts showing the signs pretty bad and the vibrations continue whether the car is in drive or not and its thru out the rpm range
 
This was on my 420a NA eclipse, my talon is the only one turbo'd. I did a leakdown but eveything checked out, yesterday i swapped fuel injectors but no change as far as the plug conditions. The sensors checked out working along with fuel, spark and air but for some reason the computer is advancing or retarding spark too much and/or injector duty cycle or so ive concluded
 
Well ive checked the harmonic balancer and its fine with no cracks or anything. Started thinking tho what if maybe a faulty ISC valve is faulty causing it to mess up air/fuel ratios either by being stuck open or closed however i have no problems maintaining a certain idle and it doesnt die or anything. Idles at a steady 700 rpm, does anyone know of any other sensor that might control ignition or injector timing besides the crank and cam sensor?
 
well the only things that could cause vibration like that would be: your tires unbalanced or worn with flat or dimple spots, also vibration could be caused by worn brakes pads and or rotors, if your alinement is off that could cause vibration, or if your clutch plates starting to go or is worn enough it will cause vibrations the only other thing i could think is if like a motor mount was loose or missing your motor would probably cause it to shake
 
Yea a lot of people thought tires but it does it at idle, not moving, in neutral so that eliminates the tires and balancing. All motor mounts are in good condition, none are cracked or sagging. Been driving for 3 months now everyday and gone out of town a few times but still isnt throwing a cel and isnt getting worse but it isnt getting better LOL its almost time for an oil change again so ill pull the pan and see if anything is in there after 3 months but i doubt that will turn up anything
 
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