Exhaust vibration??

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josegumby
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Exhaust vibration??

Post by josegumby » Wed Jan 08, 2020 2:27 am

Hello, I've recently made the purchase of both a WPS-500X as well as the starter NVH kit. I decided to start learning it on issues currently presented on my car, and my wife's car. My wife's car is a 2001 Honda Civic with a manual transmission, which we've had since it was brand new. Over the last year or so, it has developed a really loud and annoying rattle which seems to start around 2500 RPM and seems to get louder with higher RPM. 3000 RPM seems to be the sweet spot. I *swear* it sounds like it's coming from the exhaust, but it's really difficult to reproduce with no load with in my driveway.

At first, I started testing in-cylinder with the WPS-500, looking for back-pressure. And then went into the exhaust manifold where the O2 sensor would normally go. While I DO see some back-pressure, especially during a throttle-snap, I am unsure about the results, as I just can't seem to make heads or tails of the results. The front catalyst was replaced about a year ago due to cracks in it causing a P420. I wonder if pieces of the front catalyst fell out and are now rattling inside the front of the rear catalyst. Or maybe the leaking manifold caused a false lean reading on the O2, calling for more fuel, and partially melting one or both CATs... Hmmm....??

So I decided I'd try the NVH kit, since I AM dealing with a really bad rattle/vibration. I didn't expect to see any smoking gun, as the rattling noise sounds seem very random to the human ear. But first I need to explain my setup before talking about the results:

1. The cheap USB-to-OBDII connecter that works for my Honda Element, doesn't seem to work for the Civic (I'm on the fence about getting the mongoose from drew-tech, but worried that it, too, might not work on the Civic). Perhaps it's not working because the Civic doesn't use a CAN bus, but only a K-Line (where the Element uses a CAN bus). So anyways, I connected Channel D to the PCM *control* wire for the 3-wire cylinder#1 COP (0-5 volt square wave). I would not have done this if it were a 2-wire coil.

2. Since this wire will only pulse once for every TWO engine rotations, it's reporting exactly HALF the actual RPM. The software will not allow me to define half (0.5) pulses per RPM. To get around this, I clicked the "add vibration button", and unchecked everything, and added 4 custom vibrations, EN1, EN2, EN3, and EN4, using E1 as the source and a correction factor of 2, 4, 6, and 8, respectively.

3. Without a speed signal from the OBDII connector, I only have RPM info, but the rattling does seem somewhat related to engine RPM, as far as volume goes, starting at around 2500 RPM.

4. I placed the accelerometer on the passenger seat rail, in a vertical orientation.

I was a little surprised seeing the results. The rattle DOES seem to coincide with a second order engine speed. During most of the drive, the EN2 marker is coinciding with the blue (fore/aft) channel raising in amplitude. Also during this time I do NOT hear/feel the vibration. But near the end at higher RPMs, where I dropped a few markers, I noticed the GREEN (lateral) channel increasing in amplitude very dramatically, simultaneously and exactly when the offending vibration occurs. When switching to the 3-D frequency, since the TIME domain is also shown with the amplitude, the green peaks line of *perfectly* with the EN2 vibration.

There are two exhaust pressure pulses for every engine rotation, which makes me feel like an exhaust vibration is plausible; however, I'm confused by the fore/aft vibration, switching to a lateral vibration as soon as the rattling noise starts. What sort of things under the hood (at E2 frequency) would be causing the lateral vibration especially?

This is my first week using the NVH tool, looking back, I realize I was already at the PCM, and I could have just connected in at the crank sensor, instead of the coil trigger (doh!).

I will attach the NVH file, as well as all of my PSDATA files for in-cylinder and in-manifold back-pressure captures, just in case anyone is interested. As well as a few pictures that illustrate my setup.

Thank you in advance for any help pointing me in the right direction.

Thanks,
Curt
Attachments
wps500x_in_o2_throttle_snap.psdata
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wps500x_in_o2_idle.psdata
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wps500x_in_o2_3000_RPM.psdata
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WPS500x_in_cyl_3_throttle_snap_possible_exhaust_restriction.psdata
(480.31 KiB) Downloaded 21 times
WPS500x_in_cyl_3_at_idle.psdata
(311.94 KiB) Downloaded 21 times
200107_VibrationAnalysiser_003.pddata
(4.29 MiB) Downloaded 30 times
20200107_195446.jpg
20200107_195033.jpg
20200107_194906.jpg
20200107_194409.jpg

Steve Smith
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Re: Exhaust vibration??

Post by Steve Smith » Fri Jan 10, 2020 5:29 pm

Hello and thank you for the post, there is a lot to get through here for sure

Tackling the exhaust back pressure first, you mentioned front catalyst replacement due to P0420, did we establish/confirm a cause or was this due to age/mileage? (You mentioned a leaking manifold)

Could you confirm if the original catalyst had broken up?

Could you hear any rattling prior to the replacement of this catalyst?

How was the power output of the vehicle prior to and after catalyst replacement?

Do you feel as though the vehicle is lacking in power now?

I ask this because of the focus on exhaust back pressure.

If the vehicle appears to perform correctly and achieve maximum rpm under full load (in a sensible time frame) then we can move our focus away from exhaust back pressure.

We could also qualify this with airflow figures if the vehicle incorporates an airflow meter? The following forum posts discuss MAF at WOT here and and here and will help to qualify your engine is breathing correctly for its given power specification

Sorry for all the questions Curt but it does help build a picture of historical events

Looking at “WPS500x_in_cyl_3_at_idle” I do not see any errors with valve timing as the formation of the four-stroke cycle looks “normal” and exhaust back pressure is minimal. The following articles will help with the evaluation of the four-stroke cycle using the WPS500
Pressure School Part 1 and Pressure School Part 2

Peak exhaust back pressure was captured at 4368 rpm in capture “WPS500x_in_cyl_3_throttle_snap_possible_exhaust_restriction” where you acquired 854 mbar
IMAGE 1.png
Image 1
Again, this is quite normal and would need to be qualified against a comparison vehicle. I don’t believe at this stage we have an issue here, especially if your vehicle is performing correctly under acceleration with the correct airflow?

The following forum post will help explain why we have this back pressure which essentially boils down to “Time

If we take a look at the peak back pressure measurement before the catalyst “wps500x_in_o2_throttle_snap” we have 237 mbar at approx. 4000 rpm which suggests the 854 mbar exhaust back pressure measured within the cylinder is predominately due to Volumetric Efficiency (VE) or inherent inefficiency of the engine (assuming engine power delivery is normal)
IMAGE 2.png
Image 2
I hope the above helps as there is a lot to digest within the included links

Moving onto NVH, great work here thank you.

The issue surrounding the inability to enter 0.5 pulses per revolution (for engine speed input) has been added as a New Feature Request for the software team to review and no doubt this will be included in future builds. Well done using the ignition coil IGT as your NVH engine speed signal and then amending the vibration orders to align with your revised speed input. It’s a good tip to share with others, thank you.

Looking at your NVH capture we appear to have a lateral vibration (Channel C Green) at the higher rpm from around 200 seconds onwards where EN2 (second order engine vibration) would appear to be the source but not necessarily the responder.

Given the engine is under hard acceleration here, E2 (EN2 here) is characteristic of a 4-cylinder engine. Not so much the lateral vibration, but an engine vibration occurring due to combustion events (2 disturbances per revolution of the crankshaft)

The following forum posts explain this engine order phenomena under acceleration here and here
IMAGE 3.png
Image 3
Based on where your markers are positioned in the signal history above, we can see that the noise occurs on approach to peak rpm during acceleration and again during the return from peak rpm during deceleration (foot-off-gas pedal)

The amplitude of EN2 does not appear excessive (under acceleration) however, it certainly brings about a vibration/rattle from something, but what?! Can we confirm no lateral movement of the engine and exhaust system?

My gut feeling is that we have a resonance from a component brought about by engine speed & load as we can hear the rattle on the approach to the recorded peak rpm and on its return from peak rpm. These are challenging (but not impossible) to find as the engine is required to be loaded and the vibration frequency from the offending component is often not linked to the frequency of any rotating component!

Think of an aerial mast resonating at its natural frequency as a result of the air flow about the mast, this is neither linked directly to road or engine speed but caused by the loading placed on the mast via wind speed and direction. More information on resonance can be found here

Dare I say it, looking at your NVH capture and the vehicle history, the symptoms you describe are typical characteristics of an exhaust system resonance and may well originate from within the replacement catalyst (was this an original replacement part?)

Exporting accelerometer data in audio format

I have exported approx. 30 seconds of audio from your capture (approx. 190 to 220 seconds) where we can listen the data captured by the accelerometer. See this process here

Below we have the audio from Channel B (Vertical) & Channel C (Lateral) axis of the accelerometer; I cannot hear the rattle from Channel C (Lateral) but I believe I can hear something from Channel B which is intriguing!
HONDA SHORT_B.wav
CH B
(248.96 KiB) Downloaded 23 times
HONDA SHORT_C.wav
CH C
(248.96 KiB) Downloaded 22 times
Looking at the photograph of your setup, channel A and B are connected incorrectly at the NVH interface. The blue cable connects to the X input on the NVH interface box and the red cable to the Y input of the NVH interface. This is not really an issue as the axis of interest is the lateral, which is Channel C connected to the Z input. (Remember ABC to XYZ)

Would it be possible to repeat this test using the microphone mounted inside the cabin, ideally with the accelerometer still in position on the seat rail? (For this you would need 2 x NVH interfaces)

This will allow the software to capture higher “audible” frequencies and perhaps allow for a closer fix on the offending frequency of the rattle. If you only have 1 x NVH interface use just the Mic which can be attached to any of the 3 NVH interface box inputs (X, Y or Z)

The process of capturing this resonance may come down to identifying the offending frequencies inside the cabin, and then locating the zone of the vehicle that emit these frequencies with the highest amplitude during the complaint condition. Repeat road tests and thorough documenting of microphone position for each test will be required.

Remember, if you relocate the mic to the engine compartment you much change the “Location” setting of the mic from “Passenger Compartment” to “Engine Compartment” during the Set-up. (Add "Notes" too, to remind you of the location of the mic for each test)

Once we have found the offending zone, we then examine components within this zone based on accessibility and probability.

I hope this helps Curt and please feedback when you can for any clarification on the items above or information on your continued diagnosis

Take care.....Steve

josegumby
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Re: Exhaust vibration??

Post by josegumby » Mon Jan 13, 2020 12:35 am

Hi Steve, thanks for all the information and insight. You have given me a LOT to go over. Once I get a chance to go over this, I'll replay with the requested information. I took the car on a test drive today, and it really wasn't cooperating much with the noise, which is a little unusual; so I will try again throughout the week, and hopefully have some more useful information.

Thanks,
Curt

josegumby
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Re: Exhaust vibration??

Post by josegumby » Tue Jan 14, 2020 9:13 pm

Okay that was a lot of info. I think you've just about dispelled my restricted exhaust theory, you have also sparked some memories about the vehicle history which may be relavent. But first, let me answer your questions:

Could you confirm if the original catalyst had broken up?
When I had the catalyst off to inspect it, it did not appear to be broken. Externally, it had cracks (holes) where the ports came together, but the internal "honeycomb" did not appear broken. I ultimately had a shop replace it, as one of the exhaust bolt holes in the aluminum cylinder head was stripped (thanks to the shop that replaced the head gasket years ago), and repairing stripped threads on a cylinder head was a little outside my comfort area, so I let a shop both fix the threads and replace the catalyst (I've been fixing my own cars for over 30 years now, but once in a while, I just prefer letting someone more experienced do certain jobs, this being one of them). Oh, not sure if I mentioned it before, but even at idle, there seems to be an air "whooshing" sound, as if compressed air is escaping somewhere. One of the things that had me thinking restricted exhaust at first.

Could you hear any rattling prior to the replacement of this catalyst?
Yes, the first I recall hearing the rattling was around Jan 2017 (the catalyst was relaced early 2019). The water pump was leaking, and while I was in there replacing the water pump, I also replaced the leaking front main seal, and the timing belt. I triple checked the cam/crank alignment using a mirror, and have since verified with the picoscope against known good waveforms. The lower timing belt cover's "seal" had completely deteriorated from the oil leak past the front main seal. I'm not sure when the noise started happening, but *I* noticed it shortly after this water pump / timing belt service (this is my wife's car). A new lower timing belt cover was purchased from Honda and I installed it shortly thereafter. I still noticed the noise afterwards, seemingly coming from the lower front of the engine underneath and forward of the driver's seat. The exhaust also runs along this path. On November 7th, 2019, I decided to take off the timing covers again for inspection. Half-expecting the timing belt to be shredded (if you only heard how it sounds in person), I had another new timing belt (from Honda again), on hand just in case. The old timing belt looked perfect. While I was in there, I also replaced the tensioner, since it wasn't done the first go-around. I also installed the new timing belt since I had already purchased it (now I have a spare, but not likely to ever use it since the car has almost 250,000 miles on it). While putting everything back together, I noticed the new timing belt cover I installed from the first go-around with this timing belt had a broken tab that holds it to the block (it's plastic). I am starting to wonder if this pesky timing belt cover is the source of my rattling/buzzing noise.

How was the power output of the vehicle prior to and after catalyst replacement?
Only the front catalyst was replaced, not the rear. The power output seemed the same.

Do you feel as though the vehicle is lacking in power now?
I have to be honest. The lack of power could very well be subjective on my part, as this isn't my car. And whenever I hear the buzzing/rattling noise, I tend to let off the gas, as I envision the timing belt rubbing on something. Even though this has proven not to be the case. It is able to accelerate ok, nothing too far out of the ordinary. It just seemed quite a bit "peppier" years ago. This could simply be that I drive a different car day-today (this is my wife's car). Using the pressure transducer and the Pico Diagnostics, all the cylinders were contibuting equally, and if I remember correctly, about 236 PSI.

We could also qualify this with airflow figures if the vehicle incorporates an airflow meter? The following forum posts discuss MAF at WOT here and and here and will help to qualify your engine is breathing correctly for its given power specification
This car does not have a MAF, only a MAP sensor. Although those articles are very fascinating, and I clearly need to spend more time in the other PICO forums. If there is a clever trick to somehow ascertain airflow using measurements from the MAP sensor, that would be pretty cool, although I suspect there isn't.

The following forum post will help explain why we have this back pressure which essentially boils down to “Time”. If we take a look at the peak back pressure measurement before the catalyst “wps500x_in_o2_throttle_snap” we have 237 mbar at approx. 4000 rpm which suggests the 854 mbar exhaust back pressure measured within the cylinder is predominately due to Volumetric Efficiency (VE) or inherent inefficiency of the engine (assuming engine power delivery is normal)
I had always understood that the max back-pressure at idle should be 0.5 - 1.0 PSI. and that the maximum back pressure at 3000 RPM was 3.0 PSI. Sorry for changing units, being in the U.S., I think in terms of PSI. If you can validate that during my throttle-snap, a lot more air is allowed to enter, as compared to holding at 3000 RPM with no load, and this is why I'm seeing 237mbar (3.4 PSI) during the throttle snap, and this would be considered normal (characterisitc of needing time for the air to exit the exhaust system), then I have learned an important lesson, and I can start looking away from restricted exhaust.

Looking at your NVH capture we appear to have a lateral vibration (Channel C Green) at the higher rpm from around 200 seconds onwards where EN2 (second order engine vibration) would appear to be the source but not necessarily the responder.
Perhaps the lower timing-belt cover could cause a lateral vibration. I'm unclear on whether it's the cause/vs. responder, but from reading in the NVH forums, I'm guessing the engine is the cause, and the timing-belt cover, if it is in-fact causing the noise, is the responder.

Given the engine is under hard acceleration here, E2 (EN2 here) is characteristic of a 4-cylinder engine. Not so much the lateral vibration, but an engine vibration occurring due to combustion events (2 disturbances per revolution of the crankshaft)
I've been having difficulties reproducing the noise with heavy throttle lately, but also of note, is that as long as I'm in the RPM "sweet-spot", I can reproduce the noise during light throttle, although not as loud.

The amplitude of EN2 does not appear excessive (under acceleration) however, it certainly brings about a vibration/rattle from something, but what?! Can we confirm no lateral movement of the engine and exhaust system?
The exhaust seems tight. The rubber hanger in the front is getting old (spongy), but still completely intact and holding. I gave it a good lateral shake the other day, and no rattle, however there is a very "timid" squeak. Which seems like it's just from the pipe being flexed. I checked it out very thoroghly, and all the heat shields, around both catalytic converters and in tact, as well as the O2 sensors and wiring are in tact and not in danger of rubbing anything (this is a Florida car, so very little rust due to warm winters). As far as whether the exhaust is shaking laterally whilst the car is under load, I am not sure, I don't have access to a dyno, much less a lift.

My gut feeling is that we have a resonance from a component brought about by engine speed & load as we can hear the rattle on the approach to the recorded peak rpm and on its return from peak rpm. These are challenging (but not impossible) to find as the engine is required to be loaded and the vibration frequency from the offending component is often not linked to the frequency of any rotating component!
I have considered something going on with the VTEC system, as it is my understanding that it is supposed to engage around 2300 RPM, pretty close to the 2500 RPM that I start to notice the rattle. I haven't looked too much into this, as the sound seems to be coming from the front lower portion of the car. On another note, the noise I am hearing sounds rather minuscule when recorded with the microphone. I have ordered the NVH upgrade kit to get a second NVH, and perhaps we can figure out how to get a better recording by going into the engine compartment. Perhaps there is something creative we can do by measuring vibration in the engine compartment as well.

Dare I say it, looking at your NVH capture and the vehicle history, the symptoms you describe are typical characteristics of an exhaust system resonance and may well originate from within the replacement catalyst (was this an original replacement part?)
Okay, so maybe not rule out the exhaust completely, but keep it in the back of our heads. If only there was a secure way to mount a good camera in the engine bay looking at the timing belt cover and/or exhaust. I'm not sure if it's an OEM exhaust of not, but then again, the rattling/buzzing noise was present before the exhaust manifold/catalyst was replaced.

channel A and B are connected incorrectly at the NVH interface
Gah!! How did I miss this?

Would it be possible to repeat this test using the microphone mounted inside the cabin, ideally with the accelerometer still in position on the seat rail? (For this you would need 2 x NVH interfaces)
I have ordered the NVH upgrade kit, so once that arrives, I'll re-run the test. I was really torn between the NVH upgrade kit and the Mongoose pro (budget only allows one at the moment). But for now, I can continue *carefully* backprobing at the PCM, so the NVH kit wins! I may go back to the ignition coil signal, as I seemed to have a poor/loose connection at the crank signal.

Would it be possible to repeat this test using the microphone mounted inside the cabin, ideally with the accelerometer still in position on the seat rail? (For this you would need 2 x NVH interfaces) This will allow the software to capture higher “audible” frequencies and perhaps allow for a closer fix on the offending frequency of the rattle. If you only have 1 x NVH interface use just the Mic which can be attached to any of the 3 NVH interface box inputs (X, Y or Z)
I did this the other day, but with the car not cooperating, the results, listening to the NVH capture were rather lackluster. I can upload them if you want, but I think we may be better off waiting until I can get both an accelerometer and a microphone going at the same time, and with any luck, the car will cooperate.

Other vehicle history: Too many small things over the years to list. Following are the possible "front-runners":

1. Lots of issues with the front lower mudguard (currently removed from car entirely), but a lot of loose plastic in the very front lower of the car, now that I think about it. Hmmmm...

2. June-2019, I purchased a used manual transmission from ebay, and rebuilt it, replacing every bearing, and synchro ring, using Honda parts. The clutch and clutch plate were also replaced. Although the noise in question occurs before and after the transmission replacement. Based on the gear ratios, the new transmission is from either an LX or a DX (this car is an HX). (The transmission rebuild class I took years and years ago finally paid off!)

I dare not list all the history, as it has had a LOT over the years to keep it going almost 250,000 miles so far, and I don't want to overload this thread with too much information.

Thank you very much for you help in the meantime. And do let me know if there's any other information that would be useful.

Curt

josegumby
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Re: Exhaust vibration??

Post by josegumby » Wed Jan 22, 2020 3:12 pm

Steve,

Success!! (I think). I think I have an idea of what might going on now, however, I'm going to keep my theory to myself for now as I'm interested in your interpretation and don't want to sway your opinion.

So... It occurred to me, that I would not be able to use the RPM squarewave/tach whilst using the accelerometer (using all 3 channels), AND the microphone all at the same time (not enough scope interfaces... I wonder if the 4823 8-channel scope would work, hmmmm). Although I could've told the software I was using two single-interface NVH units, and foregone one of the axis, I took the plunge and ordered a second NVH unit AND a mongoose pro. I'm glad I did.

I connected the microphone to the head-rest post, and I moved the accelerometer to the actual bolt on the seat-rail, in order to avoid any wobbling back and forth on the rounded rail itself.

My drive was over ten minutes, so the original PDDATA file was very large (about 128 MB) in size, and very sluggish to start playback, so I cut it in half to make the file smaller. There are four time-periods that the noise presented itself, and rather than trying to find that small (+) "add signal marker" icon while driving (which could be a little dangerous), I opted to vocally annotate when I was hearing the noise.

The noise presented itself during the following time-frames:

102 - 114 seconds
165 -180 seconds
218 - 239 seconds
255 - 270 seconds

Even after splitting the PDDATA file, it is too large to attach here. So I will attempt to share it with Onedrive here: https://1drv.ms/u/s!Aixu37bgTE4upyFFrvqACu9ntd3h?e=HCqE4Z

If this link doesn't work let me know and I will try to split it into four short files where the noise is heard and hopefully they will be small enough to attach here.

Thank you,
Curt
Attachments
20200122_074847.jpg
picoscope physical setup
20200122_073456.jpg
microphone placement
20200122_072708.jpg
accelerometer placement

josegumby
OneWave
OneWave
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Joined: Sun Aug 27, 2017 3:46 am

Re: Exhaust vibration??

Post by josegumby » Mon Jan 27, 2020 2:02 am

Well last week I posted the results of my test drive after the purchase and delivery of the mongoose pro ISO2 OBD2 adapter, as well as an additional NVH unit. Now that I'm able to see tire-order vibrations, a more complete picture comes into focus. I noticed what appeared to be a T3 vibration showing up whenever I heard the noise. So... reading the help files that come with the NVH software, one of the things that can cause a T3 is bad inner CV joint. If this were the cause, it would certainly make sense from the perspective of where the noise seems to originate from. It's practically right next to both the timing belt area as well close to where the exhaust runs, both areas that this rattle/vibration had me concerned with in the past, based on my perception of the origin of the noise. Also this would possibly explain the quick "burst" of a rattle every time I disengaged the clutch between shifts, something I previously attributed to exhaust pressures changing. I find it interesting how we as humans can be very creative in imagining circumstances to fit the symptoms, yet still be wrong. This is one of the things I really enjoy about having a scope. We can now shift from being subjective, to being objective. Black and white results. Now it's just a matter of whether or not we interpret those results correctly; not just "it sounds like that issue I had last month".

So I put the car on ramps today and gave the CV shafts a shake, near the inner tripod joint. Sure enough, there is a decent amount of play on both inner joints. I took a short video (listed below) and put it on Youtube. Besides the knock noise I can make just by pushing it up and down, there's a small visible amount of movement. I also held the inner-most part of the joint that locks into the transmission with the other hand, and I definitely feel the shaft moving separately from the inner joint. I'm not a professional mechanic, but I'm pretty sure there shouldn't be play there.

CV joint excessive play

So I ordered two new OEM CV shafts from Honda, and will be replacing the old ones once the new ones are delivered. Cross your fingers that this is it. I will post an update after the repair.

Thanks,
Curt

Steve Smith
Pico Staff Member
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Re: Exhaust vibration??

Post by Steve Smith » Mon Jan 27, 2020 5:29 pm

Hi Curt, thank you for the continued feedback and sharing your NVH journey as this will help others.

Rest assured I will follow up with you but I am a little consumed at present, sorry for the delay

Take care......Steve

Technician
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Re: Exhaust vibration??

Post by Technician » Fri Feb 07, 2020 7:49 pm

In your case this might not be the root cause of the problem, but I see many Honda's with exhaust noises causing concern, which has always been the centre exhaust silencer vibrating and touching the offside chassis/body during driving, it is positioned very close to the chassis when you look up at the silencer from underneath on a ramp.

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