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Old 05-27-2022, 11:44 PM   #26
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Would you be able to elaborate on this a little bit so I can understand better? When you say testing the frequency, how would I go about that? Are there other symptoms I could see that would indicate misfire? And when you guys say 2nd order, are you talking about the order of a modeling ODE or something else?
Monitoring O2 sensor output (even better if you have additional wide-band one with the gauge) can help to register a misfire. Misfire will show as lean condition or very low voltage output.
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Old 05-28-2022, 12:05 AM   #27
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Models with larger stiffer driveline use a rubber damper on the rear of the driveline (even the odd m51 v6 cars) or the guibo flex disc thing on m47 240s and all but early inline 6 700 diesel manual models.

The rear rubber vibe damper never seems to go bad in normal use before other parts fail/break in my experience on the large driveline M46 models & you don?t really notice it being so mushy on the clutch take-up like the flex disc on the trans output flange (tho stiffer discs are available & used on some Volvo models, even but I was thinking if the M5 thing?) , but no way to really service or replace the damper on models with rear section driveline damper,either?
3rd engine mount in rubber doesn?t seem to add vibes except on initial startup/ cranking?

Some of the 1980 model 242s I?ve had/driven were built crooked?but that was a road speed resonance thing?

Some late model cars had some noise from the axle & had rubber weights clamped to it. You see that on mid-late cycle cars sometimes?Volvo had some problems with them in warranty?.

I went thru noise shens with the SR5 to GT-S AE86 bits (factory T50 which is a lot like a tighter tolerance Japanese copy of a borg warner T5, but smaller trans over-all) until I installed the rear rubber damper GTS driveline (same u-joint sizes except rear for the GTS LSD axle I had for it) but the SR5 driveline was much the same otherwise?
I think I remember seeing a rubber damper on the driveline of the later model, m47 240 that I took some parts off of. At the same time, I?m confident that the root of my issue is driveline independent, though I?m sure the mounting setup is amplifying the issue. I?m going to install a rubber version of the mount I?ve been using to see if that smooths things out.
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Old 05-28-2022, 12:11 AM   #28
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Monitoring O2 sensor output (even better if you have additional wide-band one with the gauge) can help to register a misfire. Misfire will show as lean condition or very low voltage output.
If the misfire was intermittent would a wideband gauge be able to respond to the rapid change in ratio fast enough to register? I?ve had an aem wideband installed for a while now ever since I had lean running issues soon after buying the car. I?ll try starting the car again tomorrow and really carefully watching the gauge while I hold the car at its ?beach boys? rpm.
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Old 05-28-2022, 12:12 AM   #29
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?beach boys? rpm.
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Old 05-28-2022, 02:50 AM   #30
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Pinion angle?
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Old 05-28-2022, 09:46 AM   #31
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Originally Posted by TheLoganZilla View Post
Would you be able to elaborate on this a little bit so I can understand better? When you say testing the frequency, how would I go about that? Are there other symptoms I could see that would indicate misfire? And when you guys say 2nd order, are you talking about the order of a modeling ODE or something else?
Even order harmonics (half, double, etc) would indicate the vibration is directly related to the engine rotating, but sympathetic (something shaking, tapping, droning in a separate part) or geared up or down at double or quadruple, or half (etc) speed. Even frequencies mathematically.
I worked in a few shops way back thad had a reed tachometer, kind of expensive but will show the frequency. If the engine was at 3000 and the shake was 50hz, that is 1:1, or first order. It?s probably a flywheel or balancer on the front of the crank in a car sittind still, or also possibly the driveshaft if in a 1:1 gear while moving. (3000/60sec=50) If it was half that, or 25hz, in a car moving in a 1:2 gear ratio, it is the driveshaft. Half speed could also be a misfire in a 4cyl, but it feels different and gets harsher under load.
You can also get even order vibrations in a broken motor mount or even a bolt or nut jammed in between 2 parts that should be isolated.
Random (unrelated mathematically) vibrations can be an odd gear ratio. Real slow mathematically related vibrations are usually wheel/axle, due to the final drive reduction.
Odd order vibrations that change order with rpm usually fall into the unattached random parts waving around due to rom or road shake or whatever.
Higher freq is usually a lightweight parts (cat shroud), lower freq is usually heavy (long exhaust pipe) when it comes to rando parts.

When picoscopes started getting popular i took some classes and we messed around with transducers. You can do up to 4 channels (i think?), and plug in a speed sensor, crank, pressure, shake, whatever. It?s pretty cool, but i never pulled the trigger on buying one.
https://www.picoauto.com/products/no...g/nvh-overview
Is the link to a vid about it.
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Old 05-28-2022, 10:38 AM   #32
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Originally Posted by TheLoganZilla View Post
Would you be able to elaborate on this a little bit so I can understand better? When you say testing the frequency, how would I go about that? Are there other symptoms I could see that would indicate misfire? And when you guys say 2nd order, are you talking about the order of a modeling ODE or something else?
There are phone apps where you can clamp the phone to something somewhat firm on the car and it will tell you the frequency of the most prominent vibration. I used one recently to diagnose a very intermittent rumble on the highway in my truck-- it turned out to be one of the wheels. It takes some math to figure out the frequency of the wheels, engine, driveling rotating. and like stated, it could be a harmonic of something.
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Old 05-28-2022, 12:52 PM   #33
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We have the Pico NVH kit with a magnetic base three axis accelerometer. The sensor gets mounted to the driver seat track.

I've also used a reed mechanical device to determine frequency of a vibration.
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Old 05-28-2022, 02:23 PM   #34
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Pinion angle?
With the entire driveline of the car removed, the buzz is still present at the same rpm, so I?m confident the transmission, driveshaft, and diff are all not the cause, nor are any of the angles between them. I am sure that reinstalling the transmission will make the problem more noticeable, but that?s due to the polyurethane bushing I believe.
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Old 05-28-2022, 02:27 PM   #35
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Originally Posted by esmth View Post
There are phone apps where you can clamp the phone to something somewhat firm on the car and it will tell you the frequency of the most prominent vibration. I used one recently to diagnose a very intermittent rumble on the highway in my truck-- it turned out to be one of the wheels. It takes some math to figure out the frequency of the wheels, engine, driveling rotating. and like stated, it could be a harmonic of something.
This sounds very interesting. I?ll have to look into the math and methods behind using frequencies to determine where my vibrations come from. How accurate are the phone apps compared to the expensive pico equipment to anyone?s knowledge, mikep, esmth, ZVOLV?
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Old 05-28-2022, 02:38 PM   #36
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Vibration thread:

http://forums.turbobricks.com/showthread.php?t=352028

I haven't used a phone to diagnose a car. The Pico software is pretty neat. You enter tire size, rear axle ratio, and plug the laptop into the data link connector for a speed input. Connect the accelerometer to the seat frame, go for a drive, and it does all the math for you and spits out a bar graph showing whether the vibrations are Tire, Propshaft, and/or Engine vibration.

Spend some time on Youtube watching NVH videos.
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Old 05-28-2022, 06:42 PM   #37
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Originally Posted by esmth View Post
There are phone apps where you can clamp the phone to something somewhat firm on the car and it will tell you the frequency of the most prominent vibration. I used one recently to diagnose a very intermittent rumble on the highway in my truck-- it turned out to be one of the wheels. It takes some math to figure out the frequency of the wheels, engine, driveling rotating. and like stated, it could be a harmonic of something.
I?ll have to look into that, thanks.
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