Slight Vibration… looking for suggestions
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
Slight Vibration… looking for suggestions
01 C5 6spd (stock)
Suddenly I have slight vibration between 900-1300rpms which I can’t locate. And engine “maybe” very slightly down in HP. What I’ve done:
- Changed plugs and checked wires… old plugs looked ok.
- NO PCM codes
- No exhaust issues that I can see
- LTFTs are 3-7% lower (depending on rpm range) from year ago
- Motor mounts seem good, but not 100%
Bought new O2 sensors, but I doubt this will help.
I’m thinking maybe catalytic issue, but nothing’s obvious. How can I check this? Bank to bank LTFT discrepancy is minimal <2%.
Any thoughts what to check?
Suddenly I have slight vibration between 900-1300rpms which I can’t locate. And engine “maybe” very slightly down in HP. What I’ve done:
- Changed plugs and checked wires… old plugs looked ok.
- NO PCM codes
- No exhaust issues that I can see
- LTFTs are 3-7% lower (depending on rpm range) from year ago
- Motor mounts seem good, but not 100%
Bought new O2 sensors, but I doubt this will help.
I’m thinking maybe catalytic issue, but nothing’s obvious. How can I check this? Bank to bank LTFT discrepancy is minimal <2%.
Any thoughts what to check?
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
vibration is in neutral or in gear when starting from a stop. Not really noticeable when underway.
Actually after changing O2 sensors seemed to improve it greatly. But right after plugs also had the same impression then came back... so I'll give it a little time. And datalog again after some driving to compare trims and O2 switching.
Last edited by Joshboody; Sep 13, 2016 at 11:19 AM.
Racer
Joined: Aug 2003
Posts: 290
Likes: 8
From: 60 miles from BGKY
Yes--mileage is important.
Expect fuel trims to change, they do a fantastic job of adjusting for normal wear and tear (dirtier injectors and air filter for example). When I'm using HP Tuners it can be affected by a temperature swing in the same day--so expect a shift after a year.
Going to assume you've checked the basics.
If your baby is higher mileage like mine, over 100K, this may wake things up, costing a few hundred in parts:
1. Remove/clean intake manifold (you will be shocked how much oil is coating the runners). I cleaned the oil out inside the head as well. Replace the gaskets.
2. Professionally clean/balance injectors
3. New O2 sensors--mine were getting lazy according to HP Tuners, and replace MAP sensor
4. I replaced knock sensors with newer style (mine is a '98)
5. Installed a cheap DIY catch can--amazed how much oil it collects
Made a nice difference for me, and the exhaust tips have never been cleaner. Looks good in HPT. It's still not where it was once upon a time, and believe it's the 19 year old cats restricting airflow. I should have done the catch can years ago.
Expect fuel trims to change, they do a fantastic job of adjusting for normal wear and tear (dirtier injectors and air filter for example). When I'm using HP Tuners it can be affected by a temperature swing in the same day--so expect a shift after a year.
Going to assume you've checked the basics.
If your baby is higher mileage like mine, over 100K, this may wake things up, costing a few hundred in parts:
1. Remove/clean intake manifold (you will be shocked how much oil is coating the runners). I cleaned the oil out inside the head as well. Replace the gaskets.
2. Professionally clean/balance injectors
3. New O2 sensors--mine were getting lazy according to HP Tuners, and replace MAP sensor
4. I replaced knock sensors with newer style (mine is a '98)
5. Installed a cheap DIY catch can--amazed how much oil it collects
Made a nice difference for me, and the exhaust tips have never been cleaner. Looks good in HPT. It's still not where it was once upon a time, and believe it's the 19 year old cats restricting airflow. I should have done the catch can years ago.
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
- Same clutch in or depressed. And in gear starting to move.
- rpm range is idle 750ish to 1000... don't feel anytime >1000rpms. Mainly when slight rev up cause difficult to hold steady 900 to 1000rpm. But hold steady at 1200 or revving >1000 do not feel it.
- intermittent... today very noticeable at stop lights and from a stop during 20min drive to store. Then on start up and on my home not there (or very slightly noticeable).
- Do NOT feel in shiftier... more in dash, consul, body.
kinda seems like exhaust resonance thing. Doesn't really seem to be engine related.
Us vette owners are very sensitive, so feel anything different... this is driving me little nuts.
Last edited by Joshboody; Sep 13, 2016 at 10:31 PM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Get the car in the air and do a hand over hand to the entire exhaust system. Shake it and look for contact points and loose hangers. damaged rubber mounts and broken brackets. Shake the entire system and see if you can feel any body or suspension contact.
Bill
Bill
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
Think I found it... front leaf spring maybe touching oil pan. So I'll change motor mounts soon.
Jacked up the engine then started... but should have started first, then jacked up engine. Seems needs some time to settle again to confirm it.
Jacked up the engine then started... but should have started first, then jacked up engine. Seems needs some time to settle again to confirm it.
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Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
For changing mounts I'm planning to remove exhaust manifolds and just jack up engine... should this be sufficient, or need to drop subframe?
Its a HPDE car and was planning to replace with low cost $15ea aftermarket mounts... ok? Or should I consider GM (ACdelco) or maybe pricey poly?
Its a HPDE car and was planning to replace with low cost $15ea aftermarket mounts... ok? Or should I consider GM (ACdelco) or maybe pricey poly?
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
I an idiot
I be wrong again. It was the bow in the spring
Checked it on ramps today.
But can jack up engine maybe 1/3"... seems sloppy for engine mounts. May change them anyway and at same time can play with exhaust.
Had track day Sat and car performed well, so trying not to worry about it... but difficult.
Checked it on ramps today. But can jack up engine maybe 1/3"... seems sloppy for engine mounts. May change them anyway and at same time can play with exhaust.
Had track day Sat and car performed well, so trying not to worry about it... but difficult.
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
Unless you have a ridiculous amount of power, I wouldn't bother with the poly mounts. But ymmv.
You say you're looking for a vibration, but you're looking at all sorts of things that are more likely to cause a miss.
How about vibration dampener? Is it wobbling a little? Pulleys on the motor running true, no noises?
Does it seem like it's in the driveline? Torque tube couplers possibly worn out?
I can think of a lot of things I'd investigate before changing O2s for a 'vibration'
You say you're looking for a vibration, but you're looking at all sorts of things that are more likely to cause a miss.
How about vibration dampener? Is it wobbling a little? Pulleys on the motor running true, no noises?
Does it seem like it's in the driveline? Torque tube couplers possibly worn out?
I can think of a lot of things I'd investigate before changing O2s for a 'vibration'
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
Thanks for the notes. I changed O2's because easy and planned to anyway since have 100k miles.
Balancer is marked and not slipping. And has always seemed to wobble since owning the car but think more illusion.
For driveline it's the same in gear, neutral, and clutch in... so FW or PP is possible. Maybe weight fell out, which I can check when doing the mounts.
Feels like exhaust resonance to me, but can't find anything. Ordered cheap motor mounts and will replace sometime. I'll update if I ever find it.
Balancer is marked and not slipping. And has always seemed to wobble since owning the car but think more illusion.
For driveline it's the same in gear, neutral, and clutch in... so FW or PP is possible. Maybe weight fell out, which I can check when doing the mounts.
Feels like exhaust resonance to me, but can't find anything. Ordered cheap motor mounts and will replace sometime. I'll update if I ever find it.
Racer
Joined: Jan 2013
Posts: 470
Likes: 58
vibration analzer
GM dealerships are issued a vibration analyzer, which is supposed to be sophisticated and able to zero in on the source. Talked to a local mechanic who said nobody ever uses it, it's covered with dust. I went to a bigger city and had a GM Certified mechanic use his, and GM told him the vibration was within factory tolerances, even though it evolved since I bought the car. Conventional wisdom seems to be let it go and when/if it gets worse, then diagnose it. Seems primitive this day in age, but that's what I was told.
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
GM dealerships are issued a vibration analyzer, which is supposed to be sophisticated and able to zero in on the source. Talked to a local mechanic who said nobody ever uses it, it's covered with dust. I went to a bigger city and had a GM Certified mechanic use his, and GM told him the vibration was within factory tolerances, even though it evolved since I bought the car. Conventional wisdom seems to be let it go and when/if it gets worse, then diagnose it. Seems primitive this day in age, but that's what I was told.
This whole thing about telling him the crank is bent is bs. The people at the dealership need a good kick in the nuts.
Racer
Joined: Jan 2013
Posts: 470
Likes: 58
I have a really nice vibration analyzer here. It's called eyes. If I see the thing running out .015, then it needs replaced. It really ain't rocket science.
This whole thing about telling him the crank is bent is bs. The people at the dealership need a good kick in the nuts.
This whole thing about telling him the crank is bent is bs. The people at the dealership need a good kick in the nuts.
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
That's not an illusion... And no, it should not look even one bit like it wobbles. It needs replaced. I bet if you put an indicator on it and turn the crank (obviously by hand), you'll see it'll be off by roughly one mile.
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 786
Likes: 46
From: Tucson, AZ
I've marked both the bolt and the outside of the balancer with NO movement. I assume a wobble comes from either walking on the crank or outer ring bond slipping?
Part of me wants a bad balancer, cause then I can do cam/heads
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
I'll look into this. But it has looked the same for maybe 15k miles including 20+ track sessions. The vibration is a very recent thing.
I've marked both the bolt and the outside of the balancer with NO movement. I assume a wobble comes from either walking on the crank or outer ring bond slipping?
Part of me wants a bad balancer, cause then I can do cam/heads
I've marked both the bolt and the outside of the balancer with NO movement. I assume a wobble comes from either walking on the crank or outer ring bond slipping?
Part of me wants a bad balancer, cause then I can do cam/heads
That balancer weighs 15 pounds. If it's no longer rotating concentric around that crank snout, it's going to vibrate the car. If you can see it wobble, it's bad. No balancer wobbles. yet is in balance. It might not be out far enough to shake the hell outa the car yet, but that day is coming.
Melting Slicks
Joined: Nov 2008
Posts: 3,146
Likes: 203
From: Edmonton Alberta, Canada
I am not as tech savvy as previous responses. I had a vibration experience and it drove me crazy. Well it was the water pump bearings piling up, no leaks or wobbles only some occasional belt noise. I would check all belt driven components first. Good luck.