Engine So I know this has been beaten to death, but... I have a 3k vibration

Sep 3, 2018
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Ok, so as the title states, recently I have been noticing I have a vibration that starts at about 3k and seems to drive out after 4K. So, tested at idle and vibration is there so I am pretty sure it is engine related. Previous owner had poly engine and transmission mounts installed. i know nothing about the clutch and flywheel set up. I have a balancer on the way but is taking forever to get here... my Currently balance doesn’t look awful but that doesn’t mean it couldn’t still be the case.

my issue is this... if it was a harmonic balancer issue, why would the vibration disappear after 4K?

I have seen people suggest that the exhaust could be too close to the body causing a vibration there. I do feel it mostly in the seat. But I can’t see a spot it would be contacting

open to discussion on the situation because. Just kind of curious. Thanks
 
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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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This could be a number of things. Unfortunately you will need to chase everything.

For example. A Misfire could cause this. I had a dead fuel injector and didn't know it. Car has a slight vibration at idle and 3K and would smooth out athigher RPM. Can ran strong otherwise. Pulled my codes and performed the cylinder balance test and found one cylinder was not firing. Fixed the injector and that vibration was all gone.
 

Boostedpimp

15 Year Member
May 8, 2003
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First thing I would do is remove that poly transmission mount and put a $15 stock rubber one in. The poly engine mounts are fine but that poly trans mount will give you soo much vibration you'll feel a night and day difference. May not totally be your issue but well greatly improve it and help allow you to trace down the true source if it still exist.
 
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Sep 3, 2018
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Thanks guys, for the quick response. The tranny mount is cheap enough and worth a shot. I’m not terribly annoyed by the vibration if it’s ‘normal’ hahaha. But I don’t want to cause anymore issues. I’d like to tackle the steering if I don’t need to worry about putting a motor in it.

So let me throw out a little more information. I recently installed a Holley terminator x kit, it is untuned right now, new plugs, and injectors at the time. The vibration was there prior. So I pulled the plugs after about 200 miles and they are clean as a whistle. Cylinder 8 looked the worst which I thought might be normal due to location and excess heat. Did a compression test last year (not that it couldn’t change) and they were all within reason of each other. Now I have been a VW tech my whole life and v8s are not common and we don’t have any pushrod motors so the way I know a misfire typically feels makes me question that it would even clear up after 1000rpms. If that makes sense. Maybe a dirty nozzle or poor spray pattern…

I am not doubting anything, just trying to discuss and talk through my issues on the car as well as always being open to a good solid explanation. Thanks afain
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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I drove around a full summer driving season on 7 cylinders and never realized it. Injector was dead dead dead. No resistance across it's coil.

It felt like a slight vibration mostly off idle and around 3K RPM. Car would still light up 2nd gear even on 7. I thought it was a vibration due to a bad balancer, or something in the flywheel/clutch area.

Don't rule anything out right now.


Poly trans mount is a known source of excessive vibrations as well. It doesn't create the vibs but transmits the more to the vehicle
 
Sep 3, 2018
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Also, because this is a forum and I know there is always that one guy. Let me specify, that there has not been a pushrod motor since I have been at the dealership. I am aware that air cooleds are all pushrod motors. Hahaha
 
Sep 3, 2018
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Colorado
I drove around a full summer driving season on 7 cylinders and never realized it. Injector was dead dead dead. No resistance across it's coil.

It felt like a slight vibration mostly off idle and around 3K RPM. Car would still light up 2nd gear even on 7. I thought it was a vibration due to a bad balancer, or something in the flywheel/clutch area.

Don't rule anything out right now.


Poly trans mount is a known source of excessive vibrations as well. It doesn't create the vibs but transmits the more to the vehicle
How is everyone testing on this motor for a dead cylinder?

also, I want to note, I believe this vibration was present prior to the new parts/efi. I just assumed it was driveline the last time I drove it and since it sat for a few months during the install wrote it off until I was back in the car this summer
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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With the engine idling, pull a plug wire off each cylinder and if the rpms drop that cylinder is good, no change in idle, likely the offending cylinder but I would swap the trans mount out too.
 
Sep 3, 2018
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So I did this with the injectors today. And I will definitely give it to you guys. A miss on a V8 is harder to feel then on a 4cyl. Anyways noticed an idle change on all the injectors I could pull off while running. I’ll try the spark plug boots tomorrow. From dizzy or plug side? Lol
 

96pushrod

I think they're a little easier to get off
May 15, 2018
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I see some recommend against the poly trans mount, but I’ve ran poly engine and trans mounts for years and never had vibration issues. I have had trans mount bolts which I forgot to tighten down once cause some vibration, which tightening them solved that - obviously.

I’d start by confirming the balancer and flywheel/flex plate are the proper balance. Then checking the condition of the u-joints in the driveshaft. Checking for a misfire is easy, just use a cheapo infrared thermometer or some water sprayed on the header primaries.

I Also experienced a vibration on my car (was a 96 I swapped a 5.0 into) and it was caused by a driveshaft that was out of balance. Just Like you it went away after about 3500rpm or, but was pretty pronounced before that.
 
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Sep 3, 2018
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I see some recommend against the poly trans mount, but I’ve ran poly engine and trans mounts for years and never had vibration issues. I have had trans mount bolts which I forgot to tighten down once cause some vibration, which tightening them solved that - obviously.

I’d start by confirming the balancer and flywheel/flex plate are the proper balance. Then checking the condition of the u-joints in the driveshaft. Checking for a misfire is easy, just use a cheapo infrared thermometer or some water sprayed on the header primaries.

I Also experienced a vibration on my car (was a 96 I swapped a 5.0 into) and it was caused by a driveshaft that was out of balance. Just Like you it went away after about 3500rpm or, but was pretty pronounced before that.
Yeah, I mean I get the whole reason against poly mounts but for some reason I love a stiff/tight feeling rattle box. So I am not to eager to replace the mount.

awesome idea on header primary temp change. Honestly never would of thought of it.

I can’t imagine it’s the DS with it vibrating but anything is worth a shot.
At this point though nothing seems conclusive just yet. I don’t want to throw a part at it but I suppose that’s what I was doing with ordering a balanced. Hahaha
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
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if you're still running an older TFI module it may be the cause....they can develop a miss a higher rpm.
 

2000xp8

SN Certified Technician
Aug 8, 2003
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The driveshaft is easy to rule out.
If the car vibrates while parked in neutral, it's not the driveshaft.
And while i like rubber bushings too, i'm with 96 pushrod, if there is a vibration, all the poly bushing will do is magnify it, i doubt it will physically cause it.

I'm a big fan of just replacing any questionable balancer, when those things really let go you are in for serious trouble.
 
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Sep 3, 2018
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Yeah the vibration is definitely there in neutral. My balancer is taking forever to get her but my fingers are crossed that it shows up today.
I’m really hoping this is the real typical, expected balancer vibration and I would like to get the car to the tuner. Just doesn’t seem worth it if I need to pull the motor apart
 

ThinBlue502

Advanced Member
May 7, 2019
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I went through this awhile back. Mine was a combination of harmonic balancer and driveshaft. Aluminum driveshaft was what finally stopped it.
 

2000xp8

SN Certified Technician
Aug 8, 2003
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I doubt you need to pull the motor apart.
If the balancer was completely shot, you would know it, the engine would be like one of those old school washing machines on spin cycle that shaking so bad it moves around the floor. Even at idle you are in the danger zone when that happens.
 

Bree

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Jan 12, 2021
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If it is the balancer in the process of going bad. If you follow what I mean? As the ballancer gets increasingly worse, the more the vibration will start to show up. Cyntrifical force is funny that way! Think about a tire, if you knock off a small wheel weight, it only manifests it's self at certain speeds. Hit like 65, and you have a vibration, keep going to 70mph, the vibration clears. However, the bigger the wight, the quicker the vibration shows up, and the longer it stays.
 
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ThinBlue502

Advanced Member
May 7, 2019
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I doubt you need to pull the motor apart.
If the balancer was completely shot, you would know it, the engine would be like one of those old school washing machines on spin cycle that shaking so bad it moves around the floor. Even at idle you are in the danger zone when that happens.
With mine, it was VERY noticeable at idle. Quite scary to see, actually.
 
Sep 3, 2018
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So replace the balancer… here is the worst of it. Vibration is still there though. Window seems to have gotten smaller from ~3300-3800 is which seems odd on its own. I did find that I was at 16 advanced to I pulled it back to 12. Maybe it is a misfire in that RPM range. Checked cylinders for misfiring at idle and didn’t notice one. Also? Checked primary temps and all are within 10 degrees of each other… already have an aluminum driveshaft, not that I think this is the case as it’s there while standing still and reving…
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