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Postby rudolf » Tue Jan 23, 2018 3:01 pm

Dear colleagues,

I would like to ask for some advice, interpreting the NVH. I'm new to it, and can't yet fully understand it.
The car I'm having problems with is a Volvo V50, MY 2008, 1.6 diesel engine, code D 4164 T, MT.
Owner says, the problem exists since his timing belts were changed.

Stationary, the engine, around 1300 RPM sends an annoying vibration, which can be felt through the chassis and steering wheel.
In transit, this vibration is felt between 1400-1800 RPM, in all gears.
All engine mounts have been replaced with new ones.

I have attached the NVH file, sensor was in the engine bay, on the chassis, in the middle, under the windshield, X facing forward.

Could you please give me a hint regarding the interpretation of the vibrations?

Humbly yours,

180117_VibrationAnalysiser_002 pe motor.pddata
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Re: Interpretation

Postby Steve Smith » Wed Jan 24, 2018 11:20 am

Hello Rudolf thank you for your post.

Looking at your captured data we have a considerable E2 (Second order engine vibration)

This is characteristic with 4 cylinder engines but certainly not at this level (Unless the accelerometer was mounted on the engine itself)

You mentioned in your post the accelerometer was mounted on the chassis; this should be insulated from such high vibration levels.(approx 500 mg in your capture)

Can we ensure there are no foul or alignment conditions with your engine to the chassis?
I am thinking here of a foul condition where a transfer path has been created between the engine and the chassis.

Can I ask, how was the vibration level before the timing belt installation?

Has there been any additional work carried out to the engine?
For example transmission, cylinder head, or injector removal.

Can we confirm we are 100% happy with the valve timing?

I ask this because of the Diesel Injector pump arrangement which I believe should also be timed?

I mention this because we also have a very high E0.5 vibration level which is typical of components rotating at half engine speed or a typical characteristic of a misfire (combustion anomaly)


Any feedback would be most welcome

I hope this helps, take care.........Steve
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Re: Interpretation

Postby rudolf » Fri Jan 26, 2018 11:00 am

Dear Steve, thank you for taking the time to help.

Apologies for my hastiness, you are right. The sensor was on the engine.
The measurement with the sensor in the middle, under the windshield is 180117_001, and another with the sensor on the passenger seats bolt ( LHD ) 180120_006.
I have not made measurements before the timing belt change, I didn't even think that the engine would have any problems.

We did not work on the cylinder head, but I did send the injectors to be checked, and the result was 2 injectors are underperforming.
With the help of the waveform library ( which has helped me alot ) , I could confirm that the camshaft and crankshaft are properly aligned, but measuring the current of injector #4, it seems that it is behind by 5 degrees. I have checked in TEXA, and couldn't find a way to reprogram the pump.
I will change the nozzles on the injectors and post the results.

Thank you for the support!
Wish you a carefree day!
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Re: Interpretation

Postby Steve Smith » Mon Jan 29, 2018 12:33 pm

Hello Rudolf and thank you for the feedback, no need to apologise I know what it’s like
Forgive me here as I am just trying to clarify the following:
We are unable to confirm if this vibration was present before the repairs?

Given the customer is complaining of the vibration in the cabin, lets stick to file 180120_006 where we have this E0.5 vibration which should not be present.
The image below highlights this peak E0.5 at approx.18 mg (1397 rpm)
My gut feeling is this is combustion related.

Forum E0.5.jpg

The peak at 50 Hz could be from your PC or vehicle charger (Disconnecting from the mains should remove this peak)

You mentioned injector removal, was this because of the vibration or another issue?

Have the injectors remained sealed and upright during transportation/storage etc.?

Have the underperforming injectors been replaced with the correct specification/quality and if so any relevant coding/initialisation been carried out?
My concern here is if “nozzles” are not the offending injector component

The results from injector 4 sound very odd (5 degrees retarded) does the vehicle experience excessive smoking or diesel knock? Could you supply a psdata file?

Sorry for all the questions Rudolf but it will help

With regards to the pump, my understanding is programming (if applicable) is not our concern, it’s the physical timing of the pump drive gear in relation to cam and crank as the High Pressure pulse delivered to the common rail from the Diesel Pump is critical for smooth running and balance.

Given this is looking more and more like combustion, can we confirm relative compression to be correct and then obtain the crank sensor signal over 500 ms/div at 1397 rpm (sweet spot of vibration) Keep PicoScope set at 1 Million Samples or more if possible. A single waveform should be fine where we can then graph the rpm

Can we include injector 1 for sync and injector 4 so as to evaluate cylinder contribution to crank acceleration and injector 4 timing?

Thank you again for the feedback, take care……Steve
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Re: Interpretation

Postby rudolf » Tue Feb 06, 2018 2:33 pm

Dear Steve,

Yes, I'm afraid I have only the word of the owner, who said that the vibrations exist since the repairs.
The physical timing of the belt is correct, we double checked it.
I have taken out all 4 injectors, because of the vibration, installed new nozzles and recalibrated them.
The shacking on the engine, in the engine bay, on the chassis, has gone down considerably, but it is still there. Inside the cabin, it can be barely felt.

I will post 3 captures:
-with sensor on the engine, near the flywheel
-with sensor in the engine bay, above the right side shock absorber
-with sensor on the rail of the right side seat

I didn't have time to make more, because the owner was in a hurry.
Volvo V50 rec inj right side seat rail.pddata
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Volvo V50 rec inj right shock absorber.pddata
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Volvo V50 rec inj on flywheel.pddata
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Re: Interpretation

Postby Steve Smith » Mon Feb 12, 2018 1:12 am

Hello Rudolf and thank you for the feedback.
It looks like you have got a result and the E0.5 vibration order has dropped dramatically.
I can still see it is slightly evident but this could now be down to characteristics,
If our customer is now happy, we are happy.

To help with an explanation of E0.5 I think its best we discuss at E1 and E2

E1 can be considered our fundamental engine frequency measured in Hz. (Hz x 60 = RPM)
E1 at idle is typically 850 rpm / 60 = 14.16 Hz

E1 is our first order engine vibration frequency and is hopefully low throughout the rev range.
Any excessive vibrations here could be attributed to engine balance or components creating a single disturbance per one revolution of the engine.

Alternatively it could be a vibration from an auxiliary component running at the same frequency/speed of the engine causing one disturbance per revolution of the engine. (E.g. Crank pulley, AC Compressor pulley etc.)

If E1 is one disturbance per revolution of the engine E2 (Second order engine vibration) is 2 disturbances per one engine revolution. The most common of which is due to combustion.

A 4 cylinder 4 stroke engine will experience 2 x combustion events per one rotation of the crankshaft.
The shocks /disturbances from our combustion are "felt" within the crankshaft and can be detected in the cabin by our accelerometer.

It is perfectly normal to see E2 higher than E1 when combustion is evident and the level (amplitude) of E2 need only be investigated if this becomes abnormal for the customer (Back to Back comparisons with other vehicles will help here)

You can confirm your E2 is attributed to combustion by accelerating the engine.
With the engine under load and combustion taking place your E2 level will be high.
Take your foot of the gas pedal and E2 should plummet as we experience over run fuel cut where no combustion is taking place.

If our E2 level remains high during over run fuel cut, we have a vibration from a component running at twice engine speed/frequency (E1)

So what about E0.5? This could be a component driven at half engine speed /frequency (E.g. Camshaft) or characteristic of a combustion anomaly.

Think back to E2 above (2 disturbances per one engine revolution due to 2 consumption events)
A single cylinder misfire (sorry combustion anomaly) generates one disturbance for every 2 crankshaft revolutions

The math looks like: 1 Disturbance / 2 Engine Revolutions 1/2 = 0.5

I hope this helps to explain what these E numbers refer to and how we can use the amplitude of these frequencies to determine vibration concerns with our engines

The NVH "Show Vibrate Help" section in your NVH software has an awesome explanation on engine vibration orders.

Show Vibrate Help 3.jpg
Vibrate Help

Take care......Steve
Steve Smith
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Re: Interpretation

Postby rudolf » Thu Feb 15, 2018 2:45 pm

Dear Steve,

Thank you very much for taking the time to write this detailed explanation.
I read the NVH help explanations, but I didn't grasp them fully.
All in all, almost two weeks now since the car left, and everything seems okay, customer is very happy.
I have learned alot and learning will never stop.
Once again, thank you for you help and support, I hope my problem will be of help to others too!

Best wishes! Cheers!
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