Possible engine vibration from 3500-4100 RPM under load (1 Viewer)

[Aaron04]

As the title states, I have a slight vibration under acceleration/load that starts about 3500RPM and goes to 4100RPM. It doesn't vibrate in neutral when trying to replicate the issue. I've had it happen in multiple gears and different speeds, even at high speed the vibration goes away when the RPM's drop. So it seems tied to the engine.

It's on a 03 LX470 with 140k miles. Timing belt has been changed.

My current guess is spark plugs, dirty fuel system, or possibly something transmission related.

Thoughts??


SOLVED!!!!

Skid plate that hangs off of the rear portion of the transmission was contacting the bottom of the transmission. Harmonic frequency of this plate humming against the transmission with engine vibration. Bent back to proper position and the sound is gone.

 

[Trunk Monkey]

Motor mount maybe.

 

[Aaron04]

^ Is this a common issue?

 

[Trunk Monkey]

They're rubber, they can crack over time. Just a suggestion to check.

 

[Aaron04]

I'll have a look at them, I'm not thinking that's what it is. It's more of a soft vibration, not a clunking vibration.

 

[Aaron04]

Still looking for suggestions. It is a bassy whirring sound like a drying machine.

Sounds like it is coming from the middle or rear of the car.

Definitely 3500-4000rpm only, any gear.

I've done a good check of the engine mounts. Possibly a transmission mount?

It is very rpm specific but no vibration in neutral. And not speed specific.

 

[ponytl]

that is exactly what it felt like when the fan bracket bearing went bad that I am replacing now... I think my bearing is just starting to go and even runs smooth at times but at certain points it will vibrate and I can see the wobble BUT i can not push pull on the fan and feel or see it... I drove it 15 miles from home to my shop and only noticed it a few times...

 

[Aaron04]

Interesting. Have you felt the vibration in neutral? Or just under load.

Mine is like clockwork.

 

[benc]

Typically any vibration under load is drivetrain related. U-joints would be my first guess, have you greased your drive shafts lately? To much grease in the rear slip can destroy the transfer case bearing and cause a similar vibration.
Good luck.


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[2001LC]

Under load at high RPM does sound like drivetrain. Try going down steep long hill, get up to RPM with vibration present, shift into neutral and coast. Is it gone? if so then I'd lean more to engine or trans as issue, if mounts in good shape.

One thing to consider is ignition coils. I say this only because of some info I've seen just lately. Condition happens once warmed up as heat builds in coil(s) creating spark issue. This will also damage spark plugs (foul).

At minutes ~10:39 is where he speak about this condition.


Fuel issue is also a possibility, as high RPM demands more fuel & air. A can of 44k run thought a tank of gas (10 gallon min). Then due a tune-up, make sure you check all vacuum lines & gas cap as well, and disconnect battery for 30 minutes while cleaning MAF sensor and T-body to reset PCM (computer) as part of the tune-up.

Lastly have you flush transmission regularly, all 16qt's?

 

[Aaron04]

I think I will be taking the time to flush everything out and get a good baseline. I have not done the transmission or diff's since owning the vehicle. While I don't think its the issue, it couldn't hurt.

I've also discovered that its not necessarily only under a load, but specifically at 3500-4000 RPM's. Even in 1st gear it does the same sound.

I'm starting to think that I could have bumped some exhaust pieces and its causing a harmonic resonance. It is a washing machine/helicopter blade sound. Pretty quiet and very minimal physical vibration.

I think driveline is out of the picture due to it stopping in neutral.

The transmission mount will be inspected, and I will also flush the transmission.

I have also thought to remove the "flux capacitor" beam to see if it changes the sound.

How regular and exact the vibration makes me think harmonics and not mechanics for right now, but I haven't ruled out the fan either.

Thanks for all the suggestions!

 

[2001LC]

Note on Flex capacitor. Some have a bracket in frame that will move if no bolts to hold it. Some have welded nuts.

 

[benc]

You say it's rpm related but you also say it stops in neutral? Drive line/ u-joint vibration can almost disappear in neutral.


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[benc]

Was there an issue before you laid it over?


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[SWUtah]

I don't think I ever get mine up to 3500 rpm's?

 

[Aaron04]

Was there an issue before you laid it over?


Sent from my iPhone

Yes, I can't pinpoint when it started exactly.


As for the RPM vs Driveline issue. In my experience, there isn't much in the driveline that will have an engine RPM dependent vibration. Driveline increases with speed and not engine RPM.

This issue happens at any speed and in very specific RPM ranges. I guess it could be something transmission related, but it does not worsen with higher rpm or speed, its about the same sound from 3500 to 4000.

 

[Aaron04]

I don't think I ever get mine up to 3500 rpm's?

Do you never get on the highway or get up to speed with urgency? I'm having a hard time believing this.

 

[benc]

I guess where I'm confused is you say it is rpm specific but it stops in neutral.
You are right, driveline vibe would change with speed.
Good luck! Vibrations can be a pain to diagnose.


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[Aaron04]

I guess where I'm confused is you say it is rpm specific but it stops in neutral.
You are right, driveline vibe would change with speed.
Good luck! Vibrations can be a pain to diagnose.


Sent from my iPhone

Yes it's quite strange. But it is only a vibration at that specific RPM (in gear and driving), not heard or felt from that RPM range in park or neutral.

 

[Aaron04]

SOLVED!!!!

Skid plate that hangs off of the rear portion of the transmission was contacting the bottom of the transmission. Harmonic frequency of this plate humming against the transmission with engine vibration. Bent back to proper position and the sound is gone.