Rhedalert

iTrader: (21)

My engine has a bit of a vibration when I keep the rpm at between 1200 and 2000. I notice that in park or neutral it's much more pronounced than when in drive (though I will feel it). Doesn't matter if the car is moving. Now the only thing I see out of the ordinary is my belt tensioner shakes, as if a pulley is out of round. Well everything looks good except the harmonic balancer, which shakes some. Think this may be related? I've had harmonic balancers be not quite perfect on other cars, yet I wouldn't get a symptom like this. How common is it for the LS1 harmonic balancers to come out of round, or shake when rotating? It's all original w/ 111k on it. Thanks in advance for any help.

Bad Blue WS6

iTrader: (41)

Bump for the info,,i think mine kinda wobbles to....hard to tell as the engine kinda moves,,,so i dont know if my eye is seeing that movement,,or if it really wobbles.

99NMB

iTrader: (7)

my car does the same thing, i have no idea what it is... its really f'n annoying... mine has done it ever since i did the 6.0 swap. sorry i .

3.4camaro

iTrader: (1)

motor mounts might be shitty or one of your pulleys is bad. That's the only thing I can think of.

Rhedalert

iTrader: (21)

Other than my p/s pulley having a small chunk broken off, they're all perfect and spin smoothly (except the crank pulley)

Rhedalert

iTrader: (21)

I'm gonna bump this up. The vibration is especially pronounced when you're going, say, 60mph and I drop it from OD into 3rd. In OD it's spinning about 1500 rpm's and it smooth. In 3rd it's about 2200 rpm and will vibrate like crazy. If I speed up to about 70 and get the RPM's over 2500 it goes away. I doubt it's the accessory side of the motor but I'm wondering if it's the flexplate?? The transmission, converter, and everything else should all be original to the car.

TLewis4095

iTrader: (10)

The LS based engines are internally balance so there is no harmonic balancer, but a vibration dampner is in the place of it. Yes, it is very common for them to fail & the vibration may be caused by the failure.....VERY common.

Your tensioner may wear out as well & it should not be shaking....but a bad dampner may be the cause.
Take a powerfull flashlight & look at it at an idle & you will see. If it looks out of round at all, replace it ASAP. The harmonics & sonic vibrations can destroy a crankshaft so it is nothing to ignore.

Good Luck!

Tracy

Rhedalert

iTrader: (21)

gonna bump this up again with an update. I've gotten some PM's about this vibration, so I know I'm not the only one with similar symptoms.

As I mentioned before, the vibration is most pronounced when at around 2200 rpm and the torque converter is locked up. Furthermore, if I hold about 3500 rpm at highway speeds (usually holding 2nd gear) I will almost instantly get a P0300 code. Keep in mind at anything over 2500 rpm, NO vibration is felt. It really does seem to be more of a harmonic vibration but I am unsure where it's coming from.

Relevant info:

- After getting the P0300 code, I pulled all plugs to inspect condition. All seem to be okay, showing no signs of trouble
- Performed a compression test which came up good, all cylinders at around 150 psi
- Fuel trim data is fine, no signs of unburnt fuel crossing the O2 sensor
- O2 sensors are oscillating fine
- I replaced the chipped P/S pulley anyway with an aftermarket billet piece.
- Crank pulley seems to be alright. It doesn't visibly wobble, although I do see the belt tensioner shake around a little. I ran the motor briefly in park without a belt, and the engine vibration was still there.
- Motor mounts *seem* okay. Haven't checked the trans mount.

After all this, I still can manage to trip the P0300 code when holding somewhat high RPM while driving. I have HP Tuners and did a log (hope I am logging it correctly) and during a normal drive, nothing shows up in history. Tomorrow I'm going to log instant misfire detection (previously I did history) and see what's going on. Is there any way to view freeze frame data with HPT?

I'm only harping on this because I am planning on driving this car ~1000 miles on vacation next week.

RevGTO

iTrader: (12)

A friend had his car in my other friend's shop for this problem. You could isolate a very definite vibration (feel it in the steering wheel) under no load at about 1200 rpm. We scanned and went through every conceivable swap and test as you did and could find nothing wrong. An "internal balance issue" was the conclusion.

In the time since, I've tried to isolate the same vibration on several cars - including mine. Most will do it; some more, some less.

On all these cars however, nothing is felt at speed under load. Only in park or neutral unloaded.

I think I started a thread about it and got no replies. The vibration dampner theory mentioned above might be an important lead.

Rhedalert

iTrader: (21)

Oh yeah, I'm not gonna rule out the harmonic balancer/crank pulley either. I'm going to check the condition of the tranny mount ASAP since I noticed a lot of people complained about a similar vibration, at similar RPM, resulting from either a bad mount or from using a solid mount. If my mount is bad and riding on the metal part of the bracket, that may be causing this. It doesn't explain the P0300 but then again I haven't had the chance to scan for misfire history (will try tomorrow)

Also, I took notice that the vibration is much worse in 3rd gear than in 4th at the same RPM, which again kind of leads me to a mount issue.

Rhedalert

iTrader: (21)

Did a scan this morning to determine why the PCM is setting P0300 random misfire. Here's the summary:

- Misfires are detected at higher RPM's (2500-4000, holding 2nd or 3rd gear while driving) and low to medium throttle (5-30%)
- All cylinders show a misfire at around the same time, no one cylinder is "at fault" or has an astronomically larger misfire count than the others

At least I can safely rule out an actual misfire occurring. The engine does otherwise run great and I have plenty of power.

I really want to say that this is a trans mount issue since I do "feel" vibration of the powertrain throughout the car at all times. I really thought this was the nature of the F-body (plus running a Hooker cat-back) but maybe I'm wrong.

GStam66

Honestly, my 99 Stang had the same issue, wound up being the torque converter being loose. Weird ****. :\

greatskiiiier

iTrader: (10)

if you destroy your crank you can always get a 383

Rhedalert

iTrader: (21)

LOL, true!


I truthfully hope it's nothing weird like that. The car has 131k miles on it and it's mostly all original/unmodded.

Dewey

iTrader: (1)

really out of date post but, i've replaced the crank pulley and balancer on my 5.3 and the vibration stays for me at about 1650 rpm, in or out of drive.
i also notice a tapping noise at idle when in gear. this leads me to believe that my torque converter may be loose as well. how does one go about tightening a torque converter without ripping the vehicle apart?

Rufusmagoo

Did this ever get resolved? I'm dealing with the same thing in my 2008 Sierra with 183k miles. So far it's all pointing to the lifters for the AFM/DOD. Can replicate the vibration in my garage while in park/neutral and all the mounts are new. Ordered a new oil pressure sensor filter and will eventually replace to see if the old filter is restricting oil pressure to the AFM solenoids.

Rhedalert

iTrader: (21)

Ended up selling the car before going further. Ironically I can detect a similar feel ever so slightly in my Trailblazer 5.3.

Rufusmagoo

You should look into deleting the AFM/DOD if it has it. GM will never admit a problem with it, but then why did they change how the cylinders shut down in 2016?! New for 2016, all cylinders shutdown randomly via programming, not hydromechanical spring loaded lifters. Hopefully I'm able to figure it out before one of those "special" lifters fails and shaves a lobe off my cam!! I'll keep everyone posted if I do figure it out. And thanks for the quick reply.

mjcrank42

My '02 Z28 has a vibration at 1400 that sounds similar to other posts in this thread. I may have missed it, but I don't see a resolution. Any re-direction would certainly be appreciated....before the local dealer finds something expensive.

If not, I can add to the symptoms: The car has is an unmodified LS1, 6-speed with 114K miles. I recently bought this car having no experience with this engine or transmission so it took a few days for me to decide that it wasn't normal and to make the symptoms repeatable. The vibration occurs:

- at 1400 RPM, in neutral, clutch engaged, and,
- during deceleration in gears [1,2,3,4] starting at 1400 and smoothing out at about 1200. Fifth and sixth gear were not checked.

I don't notice the vibration on acceleration. Also, I could have stopped the car, parking brake on, clutch disengaged, and transmission in any gear; this would have coupled the input shaft to the stopped wheels so that I would know that there was no rotating machinery except the engine. That was my reasoning anyway—but I forgot to do this.

These symptoms pointed to motor mounts, and maybe to a single motor mount as it shows up in deceleration only. The Chevy dealer came to the same conclusion and the mounts were replaced. In both mounts, the rubber was dry and broken. The same vibration persists and with the same symptoms and intensity.

The dealer is now going to use their 'pico-scope' for the next try. Apparently this is an expensive tool that acts like a stethoscope that provides a graph. That graph is hoped to localize the vibration. Whatever they find, I'll post here.

UPDATE:

The pico-scope points to the harmonic balancer. While it was running on the rack, they found a drip from the water pump. They wanted 1300$ for this work. The irony here is that I brought them the car three weeks ago for a pre-purchase checkout to avoid the avalanche of immediate problems I'm now paying for. There's more to this story but it's probably good that the first edit here was lost-- writing it was cathartic.

I have questions:

1: How does a harmonic balancer fail? From the factory 114K miles ago? Normal aging? Does the problem present itself as I described above? Will the crank—or anything else-- be compromised by this vibration?

2: I haven't been working on cars for 30+ years so I don't know which shops to trust anymore. Can anyone point me to a good resource near Denver, CO?

3: after 114K miles, and given the recent and current problems, is it time for a new engine? Will an LS3 crate engine go in easily? That engine is only about 5 times the cost of this water pump and balancer and who know, they could next say that the crank is damaged.

4: the forum has several threads about the troubles with harmonic balancers. Is it so difficult?

I'd like to hear reasoned opinions. Any help is appreciated

Redrokit8

Please note that this post is 2 years after the last.
I also have similar vibration issues as stated above. I have had a pestering P0420 code which will initially lead one to say it's a catalyst issue. In my case that may be true due to the fact a prior owner street raced the car and I'm pretty sure he dumped either race fuel, aviation fuel or alcohol as a cheater tactic. 2002 SS with 45,00 miles and I suspect the mileage was put on 1/4 mile at a time. No stone chips on paint or windshield and plenty of burnt rubber in rear fender wells. It is possible the internal catalyst is broken and partially blocking the smooth transition of exhaust on one or both sides. I am hoping that is the case as I do not get any other malfunction codes and fuel trims are all very acceptable with no misfires. If anyone is interested, at this late date, I will report back when the tear down is completed hopefully within a week of now. We'll see.
BTW, I installed a Magaflow exhaust system and at least one half of the vibration disappeared.