revving and rubbing vibration

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  #1  
Old 08-18-10, 06:30 PM
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revving and rubbing vibration

There are two things that concern me with my '06 Trailblazer. I bought it a year ago, and I'm pretty sure these two things weren't happening. Am I too sensitive, or are these legitimate concerns that I should have checked out?

1. Sometimes the engine will sound louder, like it is revved up. When this happens, there doesn't seem to be the same power when I push the gas pedal. It doesn't feel like the transmission isn't in gear, because it does accelerate, just not with the same thrust. It straightens itself out within a minute or two. Could it be related to the weather? It has been really hot and muggy.

2. Sometimes there is a vibration (feels like a vibration like if something is rubbing, or the vibration you feel when someone turns the bass up really high on the stereo) in my gas pedal. I've been trying to isolate when it happens...seems like it only happens at 40 mph or above. I don't feel it in the steering wheel or anywhere else, just the gas pedal.

So, can anyone tell me if I am overly sensitive, or if something is up that should be checked?

Thanks for the help.
 
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Old 08-18-10, 07:23 PM
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When the engine is "revved up", is the engine cold and you just started the engine?

Do you have an accessory on like the A/C?

Do you have a large electrical load on like headlights and fan on high?
 
  #3  
Old 08-18-10, 07:34 PM
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Is there a possibility this is just the thermostatic fan cluth engaged??? I know they make a lot of noise & when engaged,, they take a lot of power,, If the fan clutch bearing is siezed,, it should sound like this always,, but normal operation the sound will come & go,,, I hope this helps,,, Roger
 
  #4  
Old 08-19-10, 08:42 PM
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In response to Bill190: Sometimes when it is cold-just started, sometimes accelerating from a stop light. Yes, the
AC has been on, and yes, the headlights and fan have been running at the same time.

In response to Roger: I've never heard of a thermostatic fan clutch. From what you said, sounds like a possibility.

Hmm...no response from anyone about the vibration in the gas pedal.....don't know what to do with that one.
 
  #5  
Old 08-20-10, 07:16 AM
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These days anything which places an additional load on the engine is routed through the engine computer. And that includes large electrical loads which place a load on the alternator.

The engine computer will adjust idle up higher when these things are on.

Also when a vehicle is cold, they will typically idle at a faster speed until warmed up.

You could experiment a bit. Let the engine warm up a bit before driving off (if cold engine).

And turn off large loads and see what that does.

Might be normal operation.
 
  #6  
Old 08-27-10, 11:51 AM
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The Louder engine noise in conjunction with the reduced accelration is normal. These straight six motors have rather large clutch fans or cooling fans at the radiator. These fanse are hooked to a clutch and then to a pully on the engine and the pully is turned by the serpentine belt. When it is hot enough or cold enough, then fan will be engaged and put an added load on engine. These fans fully engage at idle and slowly disengage as you accelerate, at 35 miles an hour the fan should be completely disengaged and you will then feel a sudden jump in speed and power. this is absolutely normal. Vibrating pedal could be two things. Your mind, or possibly a bad motor mount. These engines have liquid filled insulators on the motor mounts to eliminate vibration. These insulators can sometimes melt or tear, and loose their internal fluid. That results in metal to metal contact at the mount which can cause the transferance of engine vibration into alot of different areas such as the firewall where the throttle pedal linkage passes through. However, when this is usually the case you will get the occasional really loud bang when you rev the motor in park and usually happens around 100,000 miles. Would not be concearned to be honest
 
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Old 08-27-10, 08:03 PM
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Thank for your clear explanation. I feel much better.
 
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