yotanut

Greetings,

I just recently purchased a 2004 Tacoma 4x4 2.7L w/ Auto ~ 95k miles. Now that the mornings are starting to cool down, I have noticed for the second time now a distinct knocking sound.

- Start Truck
- At Idle, sounds great - No Knocking
- After about 1 minute - put in "D" - Knocking begins
- Put it in "N" - Knocking goes away
- Put back in "D" - Knocking starts again
- In "D" - Knocking is consistent at first, but then begins to "cut-out" and eventually after about 30-45 seconds disappears

I never noticed this before on warmer mornings (around 50 degrees F), but the mornings are starting to get down into the 30 range. About 2 weeks ago, I had Toyota replace my tranny pan (drain plug stripped), flush w/ Toyota Type IV, drive belts replaced, battery replaced, and water pump replaced. The fluid was blackish in color before they flushed. Does anyone know what this could be coming from? I haven't been able to pinpoint the noise yet since I cannot let off the brake as it only does in when the transmission is engaged (i.e. D or R).

Thanks.

toyota4x4907

Well, set the parking brake (technically its supposed to hold the vehicle still in a drive gear with no throttle applied). And block the tires. Then you can get out and listen.

When you put it into D or R, how low do the RPMs fall? Idle in P or N should be like 750-800 rpm and in D or R should be about 600. How does the oil pressure look in all the gears? (If you have that gauge)

What does the knocking sound like? Metal on metal? Metal on plastic? Plastic on plastic? High or low pitch? When was the engine oil changed last? Does it have 5w-30 or 10w-30 or ?

yotanut

I was able to finally get a recording of the knocking noise. The audio file starts with the phone underneath the vehicle. Then about half way through I popped the hood and put the phone near the valve cover. That is when the knocking noise seem to intensify and eventually disappear. It sounded like it was coming from the engine but I cannot be certain.

Note: I started up the truck, 5 seconds later put it in D. Engaged the parking brake and began recording.

https://soundcloud.com/yotanut/toyota-knocking

Jomoka

Going away makes me think pistons slap - the pistons are a little loose in the bores until they warm up. Which really isn't a big deal - just don't go romp on it or rev it that high until a minute or so until they're warmed up.

Might also be a flat lifter or two slowly pumping up? But those would start of clattering and then go away after a bit, not appear after the engine slows down a tiny bit as it's put under a slight load.

Probably not a rod bearing knock, that wouldn't go away as the engine warmed up, it would get worse if anything.

Sounds nice and tappy, but it's hard to get a good feel for a noise from a cell hone recording. Tiny mics pic up higher tones well, not so much the deeper portion of a more solid clunking.

Kiroshu

X2 on possible piston slap. Piston slap is most prominent on a cold engine and usually almost disappears on warm-up. Most Toyota engines use forged aluminium pistons which under excessive unusal/wear piston slap appears. Piston slap from a forged piston usually comes from an oblong shape in the piston which more or less "tips" back and forward in the cylinder bore as it goes up and down. Or it could just be an engine with excessive wear with excessive piston to cylinder wall clearance. The engine obviously should be repaired but you can probably use the engine for a very long time with that piston slap.

I forget exactly what causes a forged aluminium piston to become oblong causing piston slap. I believe it has to do with engine operation with dramatic temperature changes.

Of course this is all speculation.

Verify good proper oil pressure and correct engine oil and weight. Possible its a bleed off in oil pressure from a worn bearing but difficult to say for sure.

Possible balance shaft bearings worn.

Crankshaft main bearing(s) worn.

Deeper investigation may be necessary for diagnosis.

yotanut

Thank you guys for the analysis. I have had it at Toyota for an entire week trying to have them replicate, and they cannot. It does not always do it, but seems to happen more often in cold weather. I might just have to wait until the temps drop some more. Other than this noise the truck runs good.