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Weird oscillatory vibrations at various RPMs
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trekvana
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Sep 24, 2012, 6:51 PM
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Weird oscillatory vibrations at various RPMs
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1998 chevy s10 2.2L 2WD 162K miles
i started feeling some vibrations coming from the engine when decelerating but i wasn't sure if it was from an unbalanced drive shaft so to eliminate the drive shaft i put the truck in park and here is what i found out. when i rev up the engine to about 1500 rpm i get this oscillatory vibration coming from the engine. the engine will vibrate for 2 seconds and then it will go away for 2 seconds, vibrate again for 2 seconds, go away...., etc.
i get these type of vibrations throughout the RPM range. the higher the RPMs the faster oscillatory vibrations I have - around 2500 rpm the vibrations last around 1 second. there are some RPMs were it doesn't vibrate at all. its as if the engine is hitting some harmonic frequency throughout the RPM band.
any guess as to what this may be? bad harmonic balancer perhaps?
thanks
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nickwarner
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Sep 24, 2012, 6:56 PM
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Re: Weird oscillatory vibrations at various RPMs
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Visually inspect the balancer. If the rubber in the middle is heavily cracked or bulging out in places you will need to replace it. Another thing to consider is something in the accessory drive. Does this have electric fans or a clutch fan? If a clutch fan take off the belt and repeat the test you talked about to see if the oscillation remains. It could be a fan clutch on its way out thats kicking in and out or even has a bad bearing.
By the way, nice job on the description and initial testing.
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Discretesignals
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Sep 24, 2012, 7:03 PM
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Re: Weird oscillatory vibrations at various RPMs
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Was there any repair work done before you noticed your symptoms?
How about the engine fan? Any blades cracked, broken, or missing?
If the harmonic balancer checks out and removing the belt doesn't alleviate the problem, you could be getting vibrations from the engine that you wouldn't normally feel due to broken or worn motor mounts or even grounded exhaust parts.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 24, 2012, 7:05 PM)
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trekvana
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Sep 24, 2012, 8:28 PM
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Re: Weird oscillatory vibrations at various RPMs
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No repair work done recently aside from new plugs and wires about 2000 miles ago. I get a intermittent p0342 code from time to time. Just to make sure, when you guys say to take the belt off you mean the whole sepentine belt? The engine has no accesory belts. If i take the belt off, wont the car die since alternator not charging? Also i have a pulley for the fan. Does this mean its a clutch fan?
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Discretesignals
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Sep 25, 2012, 5:10 AM
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Re: Weird oscillatory vibrations at various RPMs
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The accessory drive belt is the belt that drives the alternator, water pump, power steering pump, and ac compressor. You just want to run the engine without it long enough to determine if the vibration goes away. We are not recommending you to drive the vehicle without the belt on it. The vehicle will run without the belt on it because the battery will supply power to the electrical system.
The fan clutch is attached to the water pump pulley. You don't appear to have very much experience with vehicle repair.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
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Sep 25, 2012, 5:31 AM
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Re: Weird oscillatory vibrations at various RPMs
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Just glance at the moving belt with engine idling. It should be smooth operating, all pulleys line up and no wobble seen. If any seen then you will need to point that out SOON and have that fixed. If nothing noted it still should be witnessed by a tech or diagnosed at least by a tech in person,
T
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trekvana
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Sep 25, 2012, 7:56 AM
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Re: Weird oscillatory vibrations at various RPMs
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Ooops my bad. Thanks for the clear up discrete. I thought the serpentine belt was different from the accessory belt. Was too tired to think straight last night. That's what I figured when you guys meant just take it off and run the engine for a few seconds to see if the vibration went away. Just wanted to make sure. Dont know what was I thinking.
Discrete-what do you mean by grounded exhaust parts? I feel stupid asking this, but do you mean some electrical connections may be shorting to ground via the exhaust pipes?
Ill take the belt off and see what happens.
Thanks to all for the help so far
(This post was edited by trekvana on Sep 25, 2012, 8:00 AM)
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Discretesignals
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Sep 25, 2012, 4:03 PM
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Re: Weird oscillatory vibrations at various RPMs
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Means make sure the exhaust isn't touching anything such as the frame or other items that could allow engine vibrations to be passed on through the body.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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trekvana
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Sep 26, 2012, 8:17 AM
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Re: Weird oscillatory vibrations at various RPMs
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discrete when i read your response the first thing that came to mind once you read my message was you doing this. link deleted..............not allowed
doh!  glad to report that none of the exhaust parts are grounded.
aside from that i have an update. i looked at the fan and aside from some light surface rust it looks good. it doesn't wobble when i push/pull the fins and it offers slight resistance when i manually turn it - it goes about 1/2 revolution and stops. looking at all the other pulleys, they all look rock steady. there is very very small wobble in the crankshaft pulley. i mean you have to stare at it very hard to see the wobble in the pulley so i assume that this small wobble wouldn't be the cause for the vibration.
i'll take the belt off this weekend and see what happens. any chance that a misfiring cylinder can cause this (possibly due to a poor performing cmp sensor - i get an intermittent p0342 code)?. i dont have any misfire codes but iv'e read that you can still have a misfire without getting a cel.
(This post was edited by Hammer Time on Sep 26, 2012, 9:16 AM)
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Tom Greenleaf
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Sep 26, 2012, 8:45 AM
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Re: Weird oscillatory vibrations at various RPMs
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Quote ">>there is very very small wobble in the crankshaft pulley.<<"
I don't know what slight means but not thrilled with that,
T
(This post was edited by Tom Greenleaf on Sep 26, 2012, 8:45 AM)
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trekvana
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Sep 26, 2012, 9:13 AM
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Re: Weird oscillatory vibrations at various RPMs
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Good point T. By slight I mean if you were to look at the pulley from the side and imagine a protractor over it, with rock steady being 90 degrees vertical, then what im seeing with mine about 0.5 degrees maybe even less out of vertical wobble when its running - hopefully that helps. i attached a picture showing what i mean.
With the engine off, if I try to move it with my hand but its rock solid. When I increase the rpm the crank pulley does not wobble any less or any more. It stays the same throughout the rpm range.
(This post was edited by trekvana on Sep 26, 2012, 9:41 AM)
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Hammer Time
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Sep 26, 2012, 9:18 AM
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Re: Weird oscillatory vibrations at various RPMs
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OOOOH boy. That's the most technical but totally useless information I ever heard.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
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Sep 26, 2012, 9:25 AM
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LOL
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
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Sep 26, 2012, 12:00 PM
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Re: Weird oscillatory vibrations at various RPMs
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Sport - you don't need to work that hard. You have this intermittent vibration based on RPMs and no doubt unseen is loads on things anywhere.
This pulley is a Harmonic Balancer. Inside hub and outside where belt drives are separated by rubber vulcanized together that made Goodyear famous! Raincoats + Boots - not tires!
What it needs is a tech to look at it and pry on it and I'm not suggesting you to do it. It should behave and not move much (another techno measurement term) and if so it gotta go as that sucker can come off and render you a pedestrian and a bill for what got wrecked in doing so.
When you are observing it the 1/2 degree wouldn't cause alarm but you've also said it doesn't do it all the time and at just then you aren't watching it. It may be fine! Any noise or feeling that is new or out of ordinary is worth investigating and you are.
Noises and vibrations are somewhat hard via the web vs being there.
If/when that is ruled out those frequencies can happen in drivetrain items, exhaust even if not touching anything or who knows yet?
T
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Hammer Time
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Sep 26, 2012, 12:14 PM
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Re: Weird oscillatory vibrations at various RPMs
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If that balancer hub is moving any amount in any direction, it a a problem that needs to be resolved.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Sep 26, 2012, 12:14 PM)
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