Engine vibration/resonance

[OregonLC]

For the last 500 miles or so been getting some kind of resonance I can feel in my feet at the 1400 rpm point. Doesn't happen in N. However, it happens at all speeds, all gears, and with the TC locked and unlocked. So I'm pretty confident it's engine and not trans. Mostly noticeable at light/mid throttle pulling away from a light. Although you can feel it cruising in 2nd/3rd as well, but just at those RPM's. Can't hear anything,. Can't feel it in the wheel, only with your feet or hands on the shifter. It's not horrible, just a little annoying now that I'm looking for it.

Any ideas? Engine/Trans mounts look fine. Happens both with and without the harmonic balancer mounted. Happens with and without AC on. I did read one TSB about the LX spare tire being the cause, the solution being to reposition the spare and move it rearward. No CEL and power is unchanged so don't think it's a coil or anything ignition related.

 

[spressomon]

Not u-joint and/or driveshaft related?

 

[OregonLC]

Not u-joint and/or driveshaft related?

Would have been my guess, but I can induce it when stopped by power braking. Can't induce it, however, in N at the same RPM so it is correlated to engine load. Nor does it occur at the same RPM when coasting. Seems like an engine harmonic that's resonating which makes me think more like mounts. I suppose it cold also be something up front that's vibrating but you'd think that wouldn't go away in N. And it's actually right at 1600 rpm, not at the 1400 I had originally posted. Again, very minor just annoying when you have a slightly OCD personality.

 

[3D FJ]

Perhaps heat shield is loose around the exhaust somewhere?

 

[OregonLC]

Perhaps heat shield is loose around the exhaust somewhere?

Could be, but those usually express themselves as noise. This is vibration that is felt not heard.

 

[Gottagetone]

Did you remove this?

If so, thats is most likely the source! From what I understand it is supposed to cut out vibrations....

 

[Brock]

It cuts some vibrations and more are picked up from exhaust system as well....some people cant tell difference when removed. I am leaving mine on for now...

 

[OregonLC]

Did you remove this?

Happens both with and without the harmonic balancer mounted.

Tried both. And it doesn't feel like an exhaust noise, but more like the vehicle is picking up the resonance frequency of the engine right at the 1600 rpm point.

 

[RobRed]

How about your engine cover?

 

[OregonLC]

How about your engine cover?

It's in the shed!

The vibration/resonance is really something more felt in my feet than anything else. And it's not something you might even notice on a test drive unless you're looking for it. But you know how those things go... once you're radar has locked on you feel it every time.

Engine/trans mounts look fine, but do they perhaps harden over time? I really don't think it's TC or trans b/c a) it happens when stopped, b) it's directly related to engine speed, not vehicle speed, and c) it happens both when the TC is locked and unlocked. But I'm planning to drain/drop pan/flush trans this weekend anyway along with front diff, cv boots, driveline grease.

 

[SHAGGY101]

That is about the RPM that my exhaust is the loudest/ most resonate. This also happened to be when my silverado was the loudest as well (4.8L). It could be just the V8 in general. If it is a small vibration I would not worry about it. Just grab onto your transfer case shifter if you want to feel real vibrations!

Also, if you have done or have had some recent work done to the vehicle you could just be hypersensitive to the way the vehicle is behaving and could have been like that when it rolled off the line.

 

[RobRed]

It's in the shed!

There's your problem.

I'm hunting for a similar resonant sound. It's as if the skid plate is loose and rattling against the frame. Happens only when driving and is not the cats.

 

[lexi4darin]

You guys and your silly mods. Leave it stock like I did and you'll be fine.

Oregon - might as well try the MPG booster, post #6 for pic. Also might as well try engine cover.

After that, maybe a pulley or balancer? Try watching the serp belt while someone accel/decels the throttle in and out of the RPM range.

 

[OregonLC]

When I was flushing the trans I had the front plate off and was able to inspect more components. The front diff support bushing looks like it's about 80% through its useful life - starting to gap at the bottom. Wonder if this could be a contributor.

 

[lexi4darin]

You get this replaced or inspected further?

 

[OregonLC]

You get this replaced or inspected further?

Nope. I'm probably just going to live with it. I don't think anything is necessarily broken, it's just that the body is picking up a harmonic from the engine right at exactly 1600 rpm (and under load) At 1500 it's buttery smooth. At 1700 buttery smooth. It's just at that one point that I can feel it. I'm going to try snugging down the body mounts, engine mounts, trans mounts, etc. As I noted above, I may have a front diff mount that's getting tired.

 

[lexi4darin]

Might be easier to try putting the MPG booster, post #6 has a pic for reference, back on the truck. If this solves the problem, then there you go... and a great write up opportunity for the FAQ. If it doesn't solve the problem, then you're out 4 minutes of your life ... 2 for installing the device and 2 for removal.

 

[OregonLC]

Might be easier to try putting the MPG booster, post #6 has a pic for reference, back on the truck. If this solves the problem, then there you go... and a great write up opportunity for the FAQ. If it doesn't solve the problem, then you're out 4 minutes of your life ... 2 for installing the device and 2 for removal.

As I posted above, I've tried it both with the harmonic balancer and without. It make zero difference either way.

 

[lexi4darin]

Post #8. My bad.

Is there anything wrong with the idling or smoothness of the engine itself? I'd be looking for something similar to a gurgling/burping of the engine performance in that RPM range. Else, something is loose as a goose.

 

[OregonLC]

Post #8. My bad.

Is there anything wrong with the idling or smoothness of the engine itself? I'd be looking for something similar to a gurgling/burping of the engine performance in that RPM range. Else, something is loose as a goose.

Nope it's buttery smooth. And it's really more of a resonance in the chassis/body than in the engine. Only happens under load at that specific rpm regardless of vehicle speed or gear.