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Old 2nd December 2020, 20:38   #1
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Default Offending harmonic vibration in a diesel engine

Folks, posting this on the behalf of my close friend who is not part of TBHP community.

Vehicle: Tata Safari Storme (updated)
DOM: October 2017
Milage: 40K Kms.
Version: EX (4x2)

Symptoms: offending vibrations that peaks in between the RPM band of 1000 to 1100.

My friend is facing this problem from day one of the purchase. According to him, it was his blunder not to take test ride during pre-delivery inspection phase before sign on the dotted line.

The problem, as described by him: Car is very smooth at idling (850 RPM). Pickup is also very smooth and vibration free but when RPM needle crosses 1000 RPM, car starts vibrating and there is audible boom inside the cabin. As RPM middle crosses 1100RPM (and above), car again become vibration free. This happens in all gear positions and also during coasting.

During city stop and go traffic condition, RPM needle frequently crosses 1000 RPM so it becomes difficult to ignore offending vibrations.

Immediately after the car purchase, this problem was reported to concord dealer. He was told that this problem would be solved in first free service.

Concord service centre tried changing following parts from his brand new car to solve this problem.

1. Drive shaft
2. Engine mounts
3. Flywheel
4. Clutch plates

But the problem remained unloved. I request TBHP members to give their valuable expert opinion to solve this problem. Also Iím interested in knowing the root cause of this vibrations.

Note- Please refer screen shot. In order to remove subjectivity, my friend measured in cabin vibrations on the steering wheel using built in app of the iPhone.

Procedure: iPhone 6S plus is attached to the steering wheel using electrical insulation tape. iNVH app can measure vibration intensity using built-in accelerometer sensor. Pl. note, vibration intensity peaks at 1000 RPM. Vibration frequency is 26.12 Hrs.
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Offending harmonic vibration in a diesel engine-img_6428.jpg  

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Old 2nd December 2020, 22:02   #2
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Default re: Offending harmonic vibration in a diesel engine

Very interesting to measure the frequencies this way. Good thinking!

If you google a bit on frequencies / vibration in cars you will find several articles.

26 Hz is a bit border line. As a very generic rule of thumb, audible noise in the range of 30 - 300Hz tends to come from body resonances, usually exited through various engine harmonics.

15- 30 Hz usually comes into play on suspension components. But they are designed to transfer much lower frequencies to the body/chassis. But then again a faulty suspension component could cause this as well. But tends to play up at a given speed, rather than a specific RPM in all gears.

Given that it happens in all gears at the same RPM I think the first one, body resonance, might be your problem. It can be a real bear to verify it though.

Try and see any vibration in the body panels. So either, very carefully, have somebody check outside the window whilst driving at 1000RPM and the sound audible. Preferably put a hand on the various panels, BE VERY careful!

Try and open the doors (VERY CAREFUlly) whilst driving etc. Anything that changes the configuration of the body balance by opening something/pushing against it etc, might help to .

Good luck! Let us know what you find!

Jeroen
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Old 3rd December 2020, 09:09   #3
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Default re: Offending harmonic vibration in a diesel engine

Quote:
Originally Posted by Jeroen View Post
26 Hz is a bit border line. As a very generic rule of thumb, audible noise in the range of 30 - 300Hz tends to come from body resonances, usually exited through various engine harmonics.

15- 30 Hz usually comes into play on suspension components. But they are designed to transfer much lower frequencies to the body/chassis. But then again a faulty suspension component could cause this as well. But tends to play up at a given speed, rather than a specific RPM in all gears.
That rpm band is very specific - just past the idling speed. There's an idle air control valve that is a prime suspect in such cases. Or a fuel temperature sensor.

Was the vehicle scanned for errors at all?
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Old 3rd December 2020, 09:37   #4
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Default re: Offending harmonic vibration in a diesel engine

While I have never driven Tata Safari (or any diesel for that matter), commenting here because this felt interesting.
You've said that the vibration intensity peaks at 1000 RPM & it's ~26 Hz at that time.

A simple Hertz to RPM calculation shows this frequency to be 26 x 60 = 1560 RPM.
Could there be any other component which is running at 1560 RPM when engine is at 1000 RPM? e.g. a Power steering pump or the AC compressor?
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Old 3rd December 2020, 10:01   #5
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Default Re: Offending harmonic vibration in a diesel engine

Very interesting and i must compliment your thinking of using an Iphone and an App for measuring the frequency. Although its definitely not the correct way of measuring vibrations, it sure brings out the problem. Forget the frequency that you measure using this method as it is inaccurate since vibrations are a 3D phenomenon.

The theory of vibrations goes something like this : When two systems vibrating with independent frequencies are joined togather, the frequencies would change till both start vibrating at same frequency and that's when maximum energy transfer happens. This is called as resonance. This is what is used in radio.

In a car there are two systems: The engine and the body. Both have vibrations and natural frequencies. When the two frequencies match then there is a resonance and the audible boom is the result of that. As the engine rpm increases, the frequncies go out of sync and the resonance disappears.

Check the engine mount rubber pads and all place where the engine is connected to the body. You need to stop the engine vibrations from transmitting to the body.

Last edited by srini1785 : 3rd December 2020 at 10:08.
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Old 3rd December 2020, 11:10   #6
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Default Re: Offending harmonic vibration in a diesel engine

Try removing the belts for engine auxiliaries like PS pump, AC Compressor etc. and check.

Also, it wasn't clear from the post whether the noise occurs when the vehicle is not in motion and the engine is revved to 1000-1100 rpm. Could be an out of balance shaft.

Last edited by --gKrish-- : 3rd December 2020 at 11:11.
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Old 3rd December 2020, 12:40   #7
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Default Re: Offending harmonic vibration in a diesel engine

I am facing a similar issue on my Jetta TDI. There's an eery resonance coming in at 1500-1600rpm and staying till 2000rpm. The service centre refuse to acknowledge it but both me and my dad can clearly hear it. This occurs under all conditions, in gear, with the clutch engaged or disengaged and at all speeds.

I found the exact same phenomenon occuring in another 2.0 TDI on YouTube. Here's the video:



The owner who uploaded this video also found the cause to the problem sometime later. It was basically the air intake plumbing which was resonating most probably due to the fact that it had come a bit loose at its joints due to age. Here are the images. I plan to do something similar to my car too.

Offending harmonic vibration in a diesel engine-screenshot_2020120312380601.jpeg

Offending harmonic vibration in a diesel engine-screenshot_2020120312380001.jpeg

In short, I would suggest you take a fine comb and go through each and every part in the engine bay to solve the issue rather than replacing parts right of the bat. It might be an extremely minor issue like this one.
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Old 3rd December 2020, 13:24   #8
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Default Re: Offending harmonic vibration in a diesel engine

I have a similar issue in my Nano XTA and did not know how to put it in words. The moment I start my car there is humming sound from the engine bay. It worsens as soon as the AC is put on.
Unable to put a finger on where it is coming from. Funny thing is, if I roll up all the windows, the humming sound is even more clearly audible.

I have already removed and fixed both the rear panels through which the engine bay can be accessed. Additionally, I have made sure there is no metal to metal touch, like the seat belt rubbing against the body etc.

Any clue to solve this would highly help!
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Old 3rd December 2020, 15:22   #9
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Default Re: Offending harmonic vibration in a diesel engine

Resonance occurs in every mechanical structure - including cars.
What happens is that either we don't notice it or the resonant peak occurs at non frequented conditions.

1) Anyone on this forum who has the exact same make/model/version of the vehicle: if they can verify that the same happens or doesn't happen in their vehicles.

2) Resonance effects are felt more when the frame loses rigidity or when two different systems get coupled strongly. Check if the engine mounts are worn out, suspension bushes etc.

Last edited by alpha1 : 3rd December 2020 at 15:27.
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Old 3rd December 2020, 16:02   #10
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Default Re: Offending harmonic vibration in a diesel engine

Check the air intake as he says, and also the idle air control valve

Quote:
Originally Posted by vishy76 View Post
I am facing a similar issue on my Jetta TDI. There's an eery resonance coming in at 1500-1600rpm and staying till 2000rpm. The service centre refuse to acknowledge it but both me and my dad can clearly hear it. This occurs under all conditions, in gear, with the clutch engaged or disengaged and at all speeds.
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Old 3rd December 2020, 16:09   #11
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Default Re: Offending harmonic vibration in a diesel engine

Quote:
Originally Posted by vishy76 View Post
I am facing a similar issue on my Jetta TDI. There's an eery resonance coming in at 1500-1600rpm and staying till 2000rpm. This occurs under all conditions, in gear, with the clutch engaged or disengaged and at all speeds.
Hi
My 2014 Jetta TDI has exact same issue between 1400-200 RPM.
How did you address this issue? Please share the pointer to the thread, where the solution has been provided.
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Old 3rd December 2020, 16:49   #12
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Default Re: Offending harmonic vibration in a diesel engine

The resonance starts around the time the engine is coming off idle and increasing revs. At this point the engine is asking for more air and fuel - its not getting enough of it perhaps.

Drive behind this vehicle in city traffic and observe any intermittent black smoke( it would confirm the above - if at all that is the case) , also get rid of the engine cover for the time being to make sure that is not the source.
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Old 4th December 2020, 09:15   #13
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Default Re: Offending harmonic vibration in a diesel engine

Quote:
Originally Posted by hserus View Post
and also the idle air control valve
Do diesel engines have IAC valve?
https://mechanics.stackexchange.com/...-control-valve
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Old 4th December 2020, 09:32   #14
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Default Re: Offending harmonic vibration in a diesel engine



I donít have an answer for this but why will someone get so many parts changed on his new car?

Perhaps, thatís the old TATA way of doing but in my opinion absolutely wrong way to diagnose or rectify a problem.

Sorry, but if this would have been a Toyota, the max they would have done was to give the car a wash or checked the mats.

If the manufacturer is not sure of the parts it put in a new car, they should simply stop production until they are absolutely sure of the quality of what they are going to assemble.

Quote:
Concord service centre tried changing following parts from his brand new car to solve this problem.

1. Drive shaft
2. Engine mounts
3. Flywheel
4. Clutch plates
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Old 4th December 2020, 10:30   #15
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Default Re: Offending harmonic vibration in a diesel engine

Sound whether it occurs in a narrow band frequency as here or otherwise, is one of the most difficult problems to diagnose. Concorde has done the right thing in substituting the usual suspects in the Safari Storme and it has eliminated the replaced components.
May be they should add dampeners where the sound probably originates. If it lowers in an area, that is where they should concentrate further.

A long time ago, the Ambassador car I was driving developed a grating sound from the front at any speed. The FNG chap suspected the clutch and he replaced it to no avail. I had fitted an Isuzu diesel engine earlier and I was anxious to rule that out. I friend took a ride in my car one day and he heard the grating sound as usual. He pulled out the front panel and adjusted the cable connecting to the speedometer. The sound vanished after that.
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