3.4L Engine Knock (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.

 

If it only makes that sound in drive/reverse, its probably not the engine. Just my two cents.

 

sounds just like mine, no clue what it is and i have over 200,000 miles

 

Talked to a mechanic who had the same problem with his 3.4 a while back and he said it turned out to be carbon buildup on the pistons.

Once he took care of that, the knocking has completely stopped since.

Thoughts on if this could be it?

 

Seafoam your engine

Check out here for more info on seafoam: http://www.tacomaworld.com/forum/1s...y-how-thread-compiled-list-helpful-links.html

With less than 50k on your engine, I find it hard to believe that is your problem.

 

Cleaned pistons of all carbon, knock is still there. Thrust bearings are w/in spec by the way.

Its loudest from the oil pan around the drainbolt area... Any other thoughts?

 

Take the oil pan off . Are you sure its not coming from your tranny? Im not expert but reason tells me that if it only knocks in drive/reverse, the knocking is something other than the engine.

Maybe have to mech take a stethoscope to your torque converter or transmission.

 

Maybe I'm old & my hearing is fucked but it kinda sounds like an exhaust leak to me...

 

Did you ever find out what it was? Mine does the something similar.

 

mines been doing that for 11 years.

 

I've been doing a bit of research on several forums and it looks like the v6 with automatic has an issue with the flex plate cracking. Most times it develops on high mileage vehicles, which isn't your case but may be worth looking into.

I think that's what is wrong with mine. I couldn't pin point the noise with a stethoscope either.

I don't hear the noise when I first start it. It's only when its idling at operating temp and in drive or reverse. And when I shift from reverse to drive I hear a clunk sound. Does yours do that?

I removed the inspection plate and didn't see anything funny but the cracks are usually towards the center. I'm going to try a get a small camera in there to get a closer look.

 

If it is a cracked flex plate it usually where it bolts to the crank. I just had my trans out about 6 months ago with about 180k and no cracks. I have that noise and have no idea what it is. Been around long enough i don't even worry about it anymore.

 

Is'nt that clunk or ding the u-joints? Couple trucks and SUVs I've had always did that.

 

This still hasn't been resolved ?? Damn I swear the more I listen the more it sounds like an exhaust leak.. Wonder if OP checked the cross over exhaust pipe behind the heads on top of transmission

 

Mine does the same but not near as loud. i just assumed mine was the famous tacoma tick

 

What I'm hearing is def. not the "tick" ( I'm lucky enough not to have it) But more of "faap faap faap" , not so much a metallic sound to it, I'm damned curious now as to what it is....

 

From about 8 seconds to the end it def sounds like exhaust , but theres other ticks too,a little head scratcher....

 

After listening again it does kinda sound like exhaust. It's hard to tell though

 

Actually that is just the opposite. If it makes the noise when put into gear, it will most likely BE an engine noise. When you put it into gear, you are applying a load on the engine which is not there in idle.

OP, you mentioned that the thrust bearing is ok, but that would be my largest suspect for what you are describing, as usually a knock noise in gear tends to BE the thrust bearing. How did you eliminate it from being suspect? The only proper way to verify would be to remove the engine and measure the thrust bearing play. I think you should place the stethoscope tip right at the engine block, near the back of the engine, not on the oil pan. The oil pan, being a thin metal, can amplify and alter the apparent direction of a noise.

 

Remove the spark(not plug) from each cylinder, one at a time, while it's making the noise. When it stops, that's the cylinder with the problem. If it continues through the whole test, it's not the pistons, or the rods.