Hoping someone can give me some guidance on this one. 2008 VW Multivan T5 - BPC engine has a severe vibration when under load. I’m struggling to come to a conclusive answer with this one, but have attached NVH file for reference.

The history on this vehicle is that it’s had the vibration for an extended period of time. One workshop rebuilt the original transmission but the problem remained so then fitted a second hand unit but the problem has again remained. It has now come to myself and it does feel like a possible misfire but I am unable to prove it. I have created a maths channel for misfire recognition, referencing injector 1. There are anomalies but cylinder contribution looks even. I have a file which is pretty big but if you wanted to see it I can put it in a dropbox or similar.

I am stumped – please let me know if you need any further information.

Cheers, Rob

Compression test and leak down test for each cylinder. Crankcase pressure at idle. Injectors back flow. Knock sensor signal under load. CKP signal under load(gear 4th from 1500 to 3500 rpm)

Looks like the file didn't upload - please let me know if you want to see it and I'll send it or put it into an online folder.

Hello and thank you for the posts

If you can upload the NVH and PSdata file to an external drive and provide the link here that would be awesome

Take care.....Steve

Thanks. Here are the links, hopefully they work - let me know if there are any issues:

NVH file - Capture taken starting in first gear, accelerating gently through. There is a slip which is recorded by "gear 4" but vehicle hadn't changed into 4th. The next dip is 4th gear and where the vibration increases in amplitude. Vehicle feels like a misfire or combustion anomaly. Any thoughts here would be greatly appreciated. https://www.dropbox.com/scl/fi/mrstmdk6 ... yg7yn5rqs9

Maths channel for misfire recognition to see if I could prove a misfire. In my opinion it looks like cylinder contribution is even but something appears to be happening every 720 degrees. Again - thoughts here would be greatly appreciated. https://www.dropbox.com/scl/fi/2736y6jc ... 378taxszlu

Appreciate any support. I'm a fairly new user to the NVH kit and am struggling to interpret what I have recorded, which certainly shows something.

Hello and thank you for the files

I will take a look ASAP rest assured.

Hello Robbo, sorry for the late reply

Looking at your NVH capture we have two issues during acceleration

One is an E0.5 which we can often (but not always) attribute to misfire (or incomplete combustion)

A further description can be found here viewtopic.php?p=86961#p86961

The other is T1 (A component rotating at the same frequency as the road wheel and tyre)

Below we can see both E0.5 and T1 vibrations above all others within the frequency view (approx. 30 mph, 1784 rpm during acceleration)
Be aware that 4th gear 30 mph may well introduce a “lugging” effect (low road speed high gear) and will certainly load the engine
.
With that said, if our E0.5 can be attributed to misfire, this is not acceptable

As road and engine speed increase, the dominate vibration is then T1; So much so that I had to rescale the Y axis to accommodate the peak vibration
Note above, the T1 marker does not sit right on top of the measured peak at 84.1 mg due to characteristic FFT processing of continually changing road/engine speed, this is quite normal.

Had our vibration been present at fixed speeds our T1 marker would sit on top of the measured peak

In order to now pinpoint this vibration (assuming the accelerometer was installed to the driver’s seat bolt in the typical orientation) we use the right click feature and select “Single” Display mode to determine the predominate offending axis
Above we can see our X axis (fore and aft blue) is the larger offender but I note that the Z axis (lateral green) is also high

In my experience, to make a vehicle vibrate laterally (side to side) you need a lot of energy and often generated by tyres or driveshafts (Think of a scenario where a large mass can be rocked side to side)

We should not however jump to conclusions and be guided by the data.

I would now keep the accelerometer mounted on the driver’s seat (measuring the X axis only) and add additional accelerometers to the front caliper bolts (measuring the X axis only) whilst ensuring the orientation of additional accelerometer reflects that of the accelerometer connected to the driver’s seat bolt. This will help with “zoning” of the vibration, i.e., which corner of the vehicle is our offender

If we only have one accelerometer, then repeat the road tests measuring at each corner of the vehicle on the same road surface keeping the test conditions identical and variables to a minimum (not always possible I know)

Moving onto your psdata file

I have noticed periodic non-uniformity in the crank shaft sensor signal which I have highlighted below. Worthy of investigation
The periodic non-uniformity does affect the math channel considerably and I wonder if the PCM has a similar issue with interpretation of this signal?

Below I have chosen to analyze the engine speed at 1784 rpm which is where our E0.5 vibration peak was most prominent (See image 1 above)
We can see above that our crankshaft acceleration does not exhibit any visible drop during each combustion event passing through the 1784 rpm band (Suggesting no misfire)

I would however inspect this capture across the entire rpm range just to be sure (Note I have amended the math channel to “crank(A,60)" which improves the resolution dramatically

Once again, note the effects of the non-uniform crankshaft signal upon the math channel

Remember, we must be guided by the data collected above and our focus must be the huge T1 vibration as the E0.5 passes by reasonably quickly (unlike T1)

The following case study might help regarding the detection of E0.5 during periods of light throttle application during cruise conditions “Tip in”

viewtopic.php?p=103362#p103362

This may be another technique to acquire E0.5 data under differing load conditions if a vibration is felt during such driving conditions

I hope this helps, take care…..Steve

Hi Steve,
I really appreciate the time you have spent here, your knowledge and input are invaluable. I will get back in touch with the customer and get the vehicle back in. I`ll let you know once i have posted the results of further testing.
This is a great learning curve and i am hopefully looking forward to getting this sorted.

Regards

Rob

Hi Steve,

I've had the customer back in and have taken some more data:

RHF caliper mounting - https://www.dropbox.com/scl/fi/rivecr2y ... i0l5t&dl=0

LHF caliper mounting - https://www.dropbox.com/scl/fi/iokkei86 ... zomhg&dl=0

Apologies for not being able to put this onto one capture. My initial analysis of this in comparison to the original capture taken from drivers seat mounting bolt - evidence is showing the T vibration has all but disappeared and an E0.5 vibration has become much more prominent and would suggest a combustion issue. Again, your thoughts here would be much appreciated.

Cheers, Rob

Hi Rob, thank you for the captures and sorry for the late reply

I have just refreshed my mind on the original symptoms and my previous reply in order to get up to speed.

Our main focus would appear to be “the huge T1 vibration as the E0.5 passes by reasonably quickly (unlike T1)”

We had an E0.5 and a T1 at 30 mph @ 1784 rpm (Image 1) followed by a dominate T1 at 34 mph @ 2039 rpm (Image 2)

In both your new captures 2008 MULTIVAN under load 4 LHF caliper mounting bolt and 2008 MULTIVAN under load 4 RHF caliper mounting bolt our road speeds are 8 mph at approx. 1700 to 1800 rpm

I can see in the vehicle Set up that RPM was acquired using channel D as your speed input; in order to display road speed, we then need to select a gear position

1. Could you confirm the correct gear position was selected?

2. At the time of capture was the displayed 8 mph correct or do we have a measurement error?

There is certainly no doubt that E0.5 is our prominent vibration between 1600 and 1900 rpm with the left-hand caliper mounting bolt demonstrating a clear increase in amplitude over the right-hand caliper mounting bolt (339 mg and 210 mg respectively) but at differing engine speeds.

Ironically no sign of the previous offending T1!?

3. Can you feel this E0.5 vibration in the cabin as you measured earlier in this thread?

I would like to repeat these tests using OBD as the speed signal input (The 8 mph road speed niggles me)

4. Do you have more than 1 accelerometer? It would be good to have the cabin vibration level as our point of reference at the same time as 1 of the caliper mounting bolts?

Moving onto your previous scope capture (Images 4 and 5), these did “not exhibit and drop during each combustion event passing through the 1784 rpm”

This would be a worthy test to repeat at the 8 mph road speeds indicated above (if they are correct!)

We also need to address the “periodic non-uniformity in the crank shaft sensor signal” as this could have a direct effect on fueling

I hope this helps, take care……Steve