Metallic grinding sound under acceleration

[WallyWest]

UPDATE

So I managed to fix this issue, it was the heat shield(s) on the cat. On mine there are two, and on the rear one there were two corners that were loose. I used some heavy duty paperclips, the black ones that are basically a small clamp, to hold the corners together. There are holes at that point through the two parts of the shield, so you could run a bolt through there, I just used what I had on hand.



Sounds as if it's coming from the engine bay, but hard to tell. It's faint, but I don't have to strain to hear it. I've only had the 4runner for a few months, but this is definitely new. Haven't heard it before today.

Best thing I can compare it to is a metal fan blade making a tiny bit of contact with a metal shroud. Just enough to give you this raspy, buzzing metal on metal sound. It's not the radiator fan though, I can definitely hear the difference when that is on.

It's not constant, I can hear a tiny bit from a stop as I begin to accelerate then it stops and comes back a little louder around 2k rpm. Definitely related to acceleration though, it's not there when just coasting or even cruising along at 45 - 50. I didn't get it any faster than that, so I'm not sure if it would be there at 65+ when the rpms get back to 2k or so.

The accessory belts are new, just replaced them a month or so back. I get a slight belt squeak when starting it, especially if it's wet out, but it goes away almost instantly. I have not inspected the timing belt yet, but I assume it is original and in need of replacing. I've got a list of stuff to do and that's near the top, but I haven't got the parts yet. Could this be the water pump, tension pulley, or something in there?

I was convinced that it was engine related, but when I parked and put it in neutral I don't hear it at all just revving the engine up. Maybe with no load on the engine it doesn't quite make it happen? Not sure.

The pitch didn't seem to change with speed, sounded the same in any gear.

This is a 2002 sport edition with 155,000 miles. Recently purchased, and based on what I've seen so far I highly doubt that any routine maintenance has been done on it.

So any ideas?

 

[jgue467]

Engine and tranny mounts good? Some flexing maybe taking place allowing some contact of moving parts. Just a thought. :cowboy:

 

[WallyWest]

Engine and tranny mounts good? Some flexing maybe taking place allowing some contact of moving parts. Just a thought. :cowboy:

They seem fine, I do have some rust but this being PA that's to be expected. I've crawled around underneath it and it doesn't look bad. My previous car had to have a frame replaced (under warranty thankfully) due to rust issues, so I know what bad looks like, lol.

And this is a very recent thing, didn't do it up until today. I guess I'll just see if it gets worse, try to figure out exactly where it's coming from.

 

[98OzarksRunner]

This is pretty common. Mine has done it for the last 40,000 miles. Resonates at 2K, 3K, 4K . . . Mine is worse when it's cold outside. Something vibrating, probably in the exhaust. Several threads about this. If you figure it out, let the rest of us know.

 

[WallyWest]

This is pretty common. Mine has done it for the last 40,000 miles. Resonates at 2K, 3K, 4K . . . Mine is worse when it's cold outside. Something vibrating, probably in the exhaust. Several threads about this. If you figure it out, let the rest of us know.

Ok, well good to know that I'm not going crazy and my 4runner isn't falling apart.

Gotta be vibration of something or another. I will duct tape and/or JB Weld everything in sight and report back. LOL

 

[gamefreakgc]

If you're sure it's coming from the engine, what your describing is probably spark knock or pre-detonation. Much more common on distributor ignitions systems since people accidentally advance timing a lot but still possible on this engine if something is out of whack.

How's your maintenance?

P.S. timing belts don't squeak, they are grooved horizontally to fit in the gears. If you hear belt squeaks then one of your new belts is loose.

 

[chimpy]

I had a ZR2 Blazer that had the same symptoms as you describe. I found out that the "honeycomb" inside the catalytic converter was coming loose and was vibrating.No check engine light btw. It wasn't completely loose which could cause a clogging issue so I immediately bought a universal converter for it and had a friend of mine at a local muffler shop install it. The sound was gone and it ran like a new truck. Just a suggestion.

 

[WallyWest]

If you're sure it's coming from the engine, what your describing is probably spark knock or pre-detonation. Much more common on distributor ignitions systems since people accidentally advance timing a lot but still possible on this engine if something is out of whack.

How's your maintenance?

Just bought it, so no idea. I'm doing timing belt, water pump, plugs, wires, etc... in the near future.

P.S. timing belts don't squeak, they are grooved horizontally to fit in the gears. If you hear belt squeaks then one of your new belts is loose.

Well, there are other things like the tensioner and water pump that run off the smooth side of the belt. I would think that a wet timing belt, from say a leaky water pump, would squeak a bit.

I've checked the new accessory belts and they seem plenty tight. But in any case I'll be removing all that stuff in the near future.

I had a ZR2 Blazer that had the same symptoms as you describe. I found out that the "honeycomb" inside the catalytic converter was coming loose and was vibrating.No check engine light btw. It wasn't completely loose which could cause a clogging issue so I immediately bought a universal converter for it and had a friend of mine at a local muffler shop install it. The sound was gone and it ran like a new truck. Just a suggestion.

That's what I was thinking today. At times it kinda sounds like it's coming from directly below me. I did remember the last time I was under there that the metal shrouds (whatever they're called) on the outside of the catalytic converters were somewhat loose. I think they may have been missing some of the bolts/clips/whatever that hold the two pieces together. I'm gonna check that out this weekend.

 

[gamefreakgc]

If your water pump is leaking, you'll see coolant dripping out of the drain hole of the timing belt cover at the bottom. But I suppose it's all a moot point anyway if you're doing the whole deal soon anyway.

 

[Dephcon]

That's what I was thinking today. At times it kinda sounds like it's coming from directly below me. I did remember the last time I was under there that the metal shrouds (whatever they're called) on the outside of the catalytic converters were somewhat loose. I think they may have been missing some of the bolts/clips/whatever that hold the two pieces together. I'm gonna check that out this weekend.

Heat shields have a tendency to break welds (since there just tacked on), but they make more of a vibrating sound. Have you greased up the U-Joints on the front and rear drive shafts? Its a part that doesn't move during stand still idle and I do believe the front one still spins when 4wd is not engaged.

 

[WallyWest]

Bump for update.