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Discussion Starter #1
I've got a knock at idle that I can't identify on my 2003 Toyota Tacoma V6 manual. It's got 38k miles on the odo.
When the noise is audible (it's not very loud), I'm unable to pinpoint it with a stethoscope from any area of the crankcase, the cams, or from the flywheel or clutch assembly. The stethoscope picks up no knocking from the water pump or any of the accessory drives either, including the AC Compressor. There is no change in the noise when the AC Compressor cycles on and off.

It's a slower knock, almost one knock per second, which suggests the bottom half of the engine. It seems to emanate from the front of the engine compartment but I cannot distinguish top or bottom, due to the noise of the fan and the engine running.
I'll be damned, I cannot track it down! It's intermittent...it comes and goes. I've been able to get a real good audio peek into the crankcase thanks to this stethoscope, but there is absolutely no knock in there, even when I'm hearing it ambiently from outside the engine.
My best current guess is that it's emanating from the harmonic balancer or one of the front pulleys, which explains why I can't pinpoint the noise with the stethoscope (I can't stick the scope on a moving pulley). There is some visual eccentricity to the balancer, I'm not sure how much is normal.

Any advice on any other tests I could perform would be appreciated. Brainstorm my friends!

Eventually I'll probably get to the point where I should just pay a technician to take a look, but I'm not there yet.
 

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I've got a knock at idle that I can't identify on my 2003 Toyota Tacoma V6 manual. It's got 38k miles on the odo.
When the noise is audible (it's not very loud), I'm unable to pinpoint it with a stethoscope from any area of the crankcase, the cams, or from the flywheel or clutch assembly. The stethoscope picks up no knocking from the water pump or any of the accessory drives either, including the AC Compressor. There is no change in the noise when the AC Compressor cycles on and off.

It's a slower knock, almost one knock per second, which suggests the bottom half of the engine. It seems to emanate from the front of the engine compartment but I cannot distinguish top or bottom, due to the noise of the fan and the engine running.
I'll be damned, I cannot track it down! It's intermittent...it comes and goes. I've been able to get a real good audio peek into the crankcase thanks to this stethoscope, but there is absolutely no knock in there, even when I'm hearing it ambiently from outside the engine.
My best current guess is that it's emanating from the harmonic balancer or one of the front pulleys, which explains why I can't pinpoint the noise with the stethoscope (I can't stick the scope on a moving pulley). There is some visual eccentricity to the balancer, I'm not sure how much is normal.

Any advice on any other tests I could perform would be appreciated. Brainstorm my friends!

Eventually I'll probably get to the point where I should just pay a technician to take a look, but I'm not there yet.
I had a similiar problem with my taco a few years ago and it turned out to be the crank pulley (harmonic balancer), it got so bad it started to rub on the front cover and would have worn through if I didn't change it. Only difference is my Taco has the 4cyl 2.7
 

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Discussion Starter #3
Found it!
I isolated the knock to the timing belt area with a stethoscope, and Toyota replaced the timing belt pulley/tensioner no charge, under warranty!
Feels good. Thanks, stealership!
 
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