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3.4L Engine Knock when warm & under load, below 1200rpm (NOT the typical 3.4 ticking)

Howdy...

I recently purchased a 2004 Tacoma TRD SR5 V6 (3.4L) and it has developed a knocking in the engine. A mechanics stethoscope has been used but its extremely difficult to pinpoint where its coming from.

I know that Tacoma's typically have a louder idle & valve noise, but this is not that at all (listen to clip below). The engine only has 47k miles on it and the timing belt, water pump, and serpentine belts were replaced at 46k (due to a leaky water pump).

The engine has been meticulously maintained and the truck was never beat on.

The "knocking" only occurs when the truck is in drive or reverse, at operating temperature, at RPMS less than 1200, and is even more audible when the A/C is on. So its something that occurs only when a load is placed on the engine.

The truck still drives great and sounds perfectly normal above 1200 rpm.

Here is a link to the sound: http://www.youtube.com/watch?v=qWnBI6yDoqI&list=UUM2LjFt6h7LhpsXdgTUtsyw&index=1&feature=plcp .

Whats weird is that it goes away after 1200 rpm, which tells me its not bearing/piston/crank related but I'm not sure.

Please let me know what you think. We're going to try a tensioner soon to see if that has any impact.
 

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Discussion Starter #2
Anyone?

Pistons are very clean, thrust bearing is w/in spec, and knock is still there.

Seems to be loudest around oil pan drain bolt area...
You can feel it the thump slightly in the shifter when sitting in the cab and in drive w/ a/c on.
 

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I can't tell anything by listening to that recording.

Hints:

The crankshaft turns twice as fast as the cams and valve train. You should be able to think about it a little and narrow down your search by the frequency of the noise.

If you have any bad bearings on the crankshaft, there will be trash in the oil.

Try draining the oil into a clean pan and inspecting it. After a motor is properly broken in, there should not be any "Metal Flake" look to the oil. If there is, it's eating something.

There should not be any "chunks" in the oil at all. If you find any, it's eating something.

you might try removing the drive belts to eliminate the alternator and stuff from the list of things it might be making noise.

Hope it's something you can fix... Good Luck!
 

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Howdy...

The engine only has 47k miles on it and the timing belt, water pump, and serpentine belts were replaced at 46k (due to a leaky water pump).
Were the timing belt, water pump and accessory belts replaced before you owned the truck, or after? Was the sound present before the work was done?
 

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Discussion Starter #5
Before I owned it.

Previous owners claim it didn't have any knock before or immediately after, but who knows.
 

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Can anyone chime in on this? My '02 3.4 just started having a noise very similar to this. I haven't had a chance to inspect in detail yet but it is definitely coming from the passenger side and sounds like the upper engine. I also have a cylinder 5 misfire although I can't feel anything nor have I lost my performance or gas mileage. I have already tried swapping coils, plugs, and injectors but the misfire stays on cylinder 5. Mechanical issue causing misfire? Seems to slow to be the crank and too deep of a sound to be a valve. I was thinking maybe a cam?
 

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I'm currently working on a 99 Taco with the 3.4. The client was told at another shop that the flywheel was cracked. Lo and behold, no cracks. Listened and found the noise in the front under the timing cover.

Removed the upper timing cover and the noise was still present. Noise was louder on the bolts for the fan pulley bracket.

We then removed the belts from the engine and the knocking is gone.

Snatched the crank pulley, but it looks good. The fan pulley however, does click when you grab and try to move it.

Still trying to pinpoint it, will update after it's fixed.
 

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Keeps coming back with the accessory drive belts on. We replaced the fan pulley bearing, harmonic balancer, and timing tensioner to no avail. Please, can someone tell me what the hell this noise is?!?!
 

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A/C idler pulley? Those are known to make noise when they age or get muddy since they are the lowest in the drive belts.
 
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