High RPM vibration, 1999 v6

I'm looking for guidance on what might be bad. My 1999 v6 5-speed with 187k miles is very smooth, until around 3500 rpm where I get a really strong vibration from the engine. It makes all the pedals and steering wheel buzz. It's definitely the engine, it happens in any gear and in neutral. The vibration is strongest between about 3500 and 4000rpm, it goes away a little as you rev beyond 4000rpm, and below 3500rpm it's very smooth. Does the harmonic balancer go bad on these things? Any other suggestions what it might be?

 

Mine also ...waiting for what others say

 

I did some more experimenting on the way home from work today, and the vibration is strongest at almost exactly 3400rpm. A little higher or a little lower and it's smooth, and the vibration is much worse when letting off the gas than when on the gas. It definitely feels like something out of balance or resonating, but I'm stumped as to what it is?

 

Check motor mounts? I wouldn't be surprised if the rubber is pretty much gone on at least one of them, and you're just feeling the normal engine vibrations resonating through the frame/cab.

 

You might be onto something, I wouldn't be surprised if that was it. Are the motor mounts easily replaced? I might swap them just to see the result.

 

Yes, but it is very rare. The rubber bond between the inner and outer parts breaks down and the outer pulley "creeps" around the inner hub showing up as timing marks that are inexplicably way off. Again this is rare and not usually associated with vibration.

Much more common is loosening of the pulley bolt. This can cause your vibration symptom and in extreme cases can damage the end of the crank along with the pulley.
Check the torque on that bolt, it's up there at 217 ft/lbs. Standard thread direction.
No guarantee but worth a check.

 

Not super easy, you need to jack the engine up a bit to get the weight off them. Get in there with a bright light and an inspection mirror and you can probably tell if they're shot, you can also wedge a tanker bar or a crowbar in there and jack it around a bit, see how much relative motion there is. Careful what you're leveraging on though. There are two on the block on either side of the frame, and one under the transfer case.

 

Thanks for the info. I checked the crank pulley bolt this morning and it's tight. Ironically I just replaced the timing belt a few weeks ago and didn't have a torque wrench that big, so I just put it in as tight as I could possibly get it. THEN I learned the bolt was not re-usable, arg! So I have the new bolt sitting in my garage, I just have to find time to swap it. I'll rent a big torque wrench when I do. But thinking back, I've had this issue for quite some time, well before I swapped the timing belt. It happens at such a narrow RPM band that it definitely feels like resonation, so I'll check out the motor mounts next.

 

Well carry on. I wouldn't sweat the "old bolt" thing other than the torque but what the heck you already have a new one. I would guess 90% of folks/shops do not replace it. Originally I replaced them but have not for quite some time.

Other than visual/jacking on the mounts a quick initial check is to put a torque load on them and see what happens. In low range hold the brakes or emergency brake and give her "momentary" shots of skinny pedal. Do this in increasing amounts and observe what the engine does, don't get carried away. Also this should not be a substitute for a good inspection.
Unless the rubber has deteriorated/torn to the point there is some metal to metal contact in the mount I doubt they would cause a resonation in neutral, but stranger things have happened.

 

That's good to know the bolt is typically OK if not replaced. I'm not sure why it's officially not-reusable, but the new bolt did come with some sort of thread locker already applied to it. Do you see that bolt coming loose often? I don't spend much time at 3400rpm so it's less that it bothers me, and more that I just want to be sure nothing is getting ready to come apart. But I would like to fix it if I can, so I appreciate your help and all suggestions are certainly welcome!

 

I give the bolts a good clean up and inspection for any kind of distortion and apply a drop of medium strength thread locker.
It's not uncommon for the bolts to loosen but I attribute that more to the installation, like low torque, lack of thread locker or general lack of cleanliness etc.

FWIW, for the first several years the 3.4 crank bolt torque spec was a bit lower and at some point the bolt itself was upgraded so apparently Toyota felt there was at least some issue. The last of the upgraded bolts I bought did not have thread locker but that was around 8 years ago.

Are all your accessory belts/pulleys running true? AC on/off make any difference?

 

Now I'm nervous because I didn't use thread locker and I've got a 2000 mile trip coming up, lol. Guess I should replace that bolt before the trip! I wonder if I can pull off the swap without having to remove all of the accessory belts and the fan and shroud? From memory, I think that pulley is far enough on the shaft that it will stay put when I remove the bolt.

The belts are all brand new and everything's running strait as an arrow. The vibration is there when the A/C is on and off. It's high frequency and lots of energy, which makes me think it originates with something with lots of rotating mass, like the crank shaft or the alternator. If I run it up to 3400rpm or 3500rpm, the vibration is there but not super strong as long as I'm on the gas, but the moment I take my foot off of the gas it gets much stronger for a second, then fades to nothing very quickly as the motor slows down. 3400rpm is definitely the rpm where it resonates, and it's definitely stronger when my foot is off the gas.

 

You should be able to R&R the bolt from below without much trouble. Remove skid and unclip the bottom piece of the shroud and work between the fan blades. The pulley will not go anywhere. Of course this will depend on the method/tool you like to hold the crank.
Speaking of fan blades, are they all there/intact?

 

Yes the fan is in good shape. I was able to get a wrench on the pulley bolt this morning from the top to check it, but very limited room to move. Hopefully there is more room from the bottom, I'll have to give it a try. It's the 5-speed manual, so to hold it still I just put the truck in 5th gear with the parking brake on tight. That worked for tightening, I removed it with an impact wrench (air wrench), hopefully there's enough room to loosen it using a breaker bar since the air wrench definitely won't fit.

 

I picked up a new adequately sized torque wrench and replaced the bolt. I was able to do it from the bottom after only removing the rock guard. A deep socket kept the torque wrench out of the pipes along the frame, and the fan shroud was flexible enough that it just flexed out of the way. It was difficult to get enough torque on it though, due to all of the flex in the drive train. I put the truck in 5th gear and the park brake on hard, and when pulling on the bolt the motor would spin pretty far before there was reasonable resistance, then when you let off of the wrench the motor would spin back the other way as the drive train unwound. But I finally got enough on it to make the wrench click, 3x to be sure! Thinking back, I probably should have put it in 4wd and had my wife stand on the brake to reduce the flex in the system.

Anyway, the vibration is still there after replacing and properly torquing the bolt.

 

I vote for the clutch / pressure plate / throw-out bearing. Will it do it setting still? If so it's not the clutch plate. If not then you might have a piece of clutch material that has came loose from the plate causing the balance issue.

 

My friend and I have been working on this same problem on my truck. Spark plug #4 is missfiring. So tomorrow we are going to change the fuel injector in that cylinder. Even after all new plugs, wires, belts, filters, etc. it still shakes a lot unless I excellerate or coast at high speeds: 70 and 80 (I commute to work).