Toyota Engine Knock

[kschachn]

Recently my '99 Toyota Sienna (1MZ-FE engine) has developed a noticeable knock when operating at certain RPMs. You can make the noise by reving up to about 2600 RPM and then it will make a louder knock when backing off just a bit. It goes away at higher RPMs. The location of the noise is hard to pin down but sounds as though it is coming from the top of the engine and only appears when warmed up.

I have used Mobil 1 in this engine since new and have changed the oil every 4500 miles or so, the engine has 150,000 miles on it now.

I did some searching here as well on Usenet but only found people posting similar questions (no real answers). Does anyone have any thoughts on what this might be before I take it to the dealer for a diagnosis?

I have a hard time believing it is wear of some sort with my OCIs and use of synthetic, but who knows. What about a bad knock sensor? I generally use 92 or better octane gas (the manual "recommends" this octane) but different gas seems to make no difference. It sure isn't what I remember "pinging" to sound like, it is much more of a deep-seated knocking that doesn't sound very nice

 

[chrome]

Could be a timing belt tensioner going bad, that would make a knock. Its hard to tell you what is wrong based on your description.

The knock you describe doesn't sound like its ignition related. "Pinging" is more high frequency, and occurs mostly when the engine is loaded when accelerating the car etc.

Things to also check for is whether the EGR system is fully functional, and also whether there is carbon fouling of the piston crowns.

Is there a CEL coming on?

 

[Drew99GT]

Timing belt tensioner would make a drowning/whining type sound from the bearing (similar to the sound of a bad alternator bearing), I would think.

Pinging would be heard more under load, in hot weather such as climbing a hill or accelerating in a higher gear.

When you say it makes the noise when you let off from 2600, that sounds like valve lash or a stretched out timing belt. My 94 Corolla made a very similar sound when decelerating until I changed the timing belt and adjusted the valves.

 

[chrome]

I am not too sure about the toyota V6 engines, but in my car (Mazda V6), the timing belt tensioner is actually spring loaded and dampened hydraulically. Over time, the spring pre-load gets weaker, and this allows the timing belt to develop some slack, which sometimes causing a knocking/low slapping sound to occur. But yes, a bad bearing will cause a whirring sound...

 

[kschachn]

Well, thank you for all your replies. On the way home from work today I stopped by the local Toyota dealer and they were very helpful, even sending out a tech to listen to the noise. He said he thought it was a bad timing belt tensioner (or idler) pulley and not a bearing noise. He said bearing noises generally occur throughout the RPM range and with the maintenance I have done, he's never seen a bad bearing in this engine. He suggested I pull the right upper motor mount and remove the timing belt cover, which I did tonight. After doing that and listening again I am about 95% sure he was right - the noise is easier to locate now and I can see the belt "jump" ever so slightly when the noise is being made.

BTW the idler pulley is bolted directly to the head which would amplify the sound a lot if that's the one that is bad.

When I replaced the belt 80,000 miles ago I did not replace the tensioner and idler pulleys, nor the water pump. He strongly suggested I do that now (along with a new belt of course) and see if that corrects the problem. Since I now have a little over 150,000 miles on the vehicle that is a good idea anyway. Looks like I know what I will be doing this weekend.

 

[kschachn]

One more question - anyone think this is a bad idea?

http://tinyurl.com/mkrmm

An online OEM dealer I usually buy from would be about $100 more. Aisin is the OEM supplier, and I think that Bando is also.