VW T6 (2018 cxha) - mystery engine jerks and judders av 2-3k rpm problems

[mr.change84]

5 minutes normal driving would be a good reference. A couple (2-5) of hard pulls to demonstrate the issue would be ideal. All of them can be in a single log. Some bookkeeping would be helpful - to time stamp when the issue surfaced - see the "Marker" above.

Will do logging today after work.

Pre. logging we will clean the manifold MAP sensor, change fuelfilter and manually regeneration of DPF.

 

[DaveD]

After you replaced the cam belt you say, "And after 200m at 3k, engine came really alive.. all was good. Pulled really strong and sound so sweet."
To me that strongly suggests you have correct timing and no bent con rods or other mechanical engine damage.

 

[mr.change84]

After you replaced the cam belt you say, "And after 200m at 3k, engine came really alive.. all was good. Pulled really strong and sound so sweet."
To me that strongly suggests you have correct timing and no bent con rods or other mechanical engine damage.

It was air inside injectors that cause it to run on 3 cylinders. And when giving 3k rpm, they really opened up and self breeding themselves

 

[mr.change84]

@mmi
engine blockmap data

 

[mr.change84]

@mmi
only thing done before the blockmap and log, was cleaning the manifoil MAP sensor with maf cleaner

log from run.
multiple marker point when car/engine war jerky/juddery

 

[mr.change84]

@mmi
Last log of the day. 2min idle, hard pull 4. gear, 2min idle.

Thank you so much for all your help, really appreciate it.

 

[mr.change84]

Status after today's work on the van.

We have done this and it has not affected the problem. Still jerks and judders around 2000-3000rpm on light throttle movment/use.

- cleaned the MAP sensor at manifoil.
- changed diesel/ fuel filter (with vcds)
- Done a stand still DPF regeneration via vcds.

 

[mmi]

Thanks for the logs. Had a brief look into the data just to eliminate the most obvious - I believe engine speed sensors (crankshaft and camshaft) are just fine. Need to have a deeper look tomorrow.

Still jerks and judders around 2000-3000rpm on light throttle movment/use.

What about when using cruise control in that rev range - e.g. gentle uphill - causing light throttle increase?
Any noticeable dual-mass flywheel issues?

 

[mmi]

Last log of the day. 2min idle, hard pull 4. gear, 2min idle.

In the log were markers at 220, 225, 241 seconds so assumed there was juddering just before then.

Interestingly engine RPM is very smooth then when accelerating (RPM increase slope) so the juddering doesn't show here.
Also turbo pressure seems to stable - however, must assuming these pulls were not at full throttle, hence the dips in the beginning?




Calculated internal torque doesn't show any spikes/drops. Neither does cylinder pressure (although data available only from cylinder 3).



As not seen clearly in the data it looks like the engine is running smoothly and makes me think more traditional cause: engine mounts, drive shaft, flywheel?

- sticking actuator/wastgate (turbo)

This can be somewhat tested by VCDS - see here

[T6_measured] 01-Engine - Built-in tests for turbocharger

HOW-TO run engine's built-in test for turbocharger Engine running VCDS > Select > Engine > Basic Settings > IDE00457 - Test of turbocharger Select "Measuring Values" Pick up e.g. the following data items for monitoring: IDE00021 Engine RPM IDE07375 Charge pressure before throttle valve...

www.t6forum.com

 

[mr.change84]

Thanks for the logs. Had a brief look into the data just to eliminate the most obvious - I believe engine speed sensors (crankshaft and camshaft) are just fine. Need to have a deeper look tomorrow.

What about when using cruise control in that rev range - e.g. gentle uphill - causing light throttle increase?
Any noticeable dual-mass flywheel issues?

tested when using cruise control, and still there. no diffrence.

 

[mr.change84]

This can be somewhat tested by VCDS - see here

[T6_measured] 01-Engine - Built-in tests for turbocharger

HOW-TO run engine's built-in test for turbocharger Engine running VCDS > Select > Engine > Basic Settings > IDE00457 - Test of turbocharger Select "Measuring Values" Pick up e.g. the following data items for monitoring: IDE00021 Engine RPM IDE07375 Charge pressure before throttle valve...

www.t6forum.com

we har done this test, and multiple others. all came out good. reported no problem.
we even stood in the engine bay and looked/touch all ic tubing etc for boost leaks.. nothing..

 

[mr.change84]

Any noticeable dual-mass flywheel issues?

i would like to say no.. no rattle, no typical DMF sound. and clutch plate are not slipping.

and yesterday I got hold of the person how used the car befor us (company we bougth it from) and he said the car was perfect up intil toothed belt "snaped"
asked it he recall any jerk or juddery movment in "low to mid" rpm, and he said NO.. nothing..

 

[mmi]

we har done this test, and multiple others. all came out good. reported no problem.

Do you mean the message: "Finished correctly" or did you have some pass/fail criteria for the tests?



I'm highly confident that the "Finished correctly" is only an indication that the test was run successfully - but there is no built-in pass/fail criteria in VCDS or in engine software. One must set up the measurements and judge the pass/fail criteria.

 

[mr.change84]

Do you mean the message: "Finished correctly" or did you have some pass/fail criteria for the tests?

View attachment 262837

I'm highly confident that the "Finished correctly" is only an indication that the test was run successfully - but there is no built-in pass/fail criteria in VCDS or in engine software. One must set up the measurements and judge the pass/fail criteria.

What you say.. finished correctly

 

[bluezie]

Going back to basics, has the engine been compression tested? Can't see it in the previous logs.
I'm sort of smelling a rat here, as in the damage is far worse than it was 'sold' with - ie a coverup to maximise saleability and profit.
If the van drove absolutely fine before the belt failed, it's very unlikely to be anything to do with fuel supply or sensors. Normally its bent rods, compression, bent valves, snapped followers, and spun camshafts. I'd even be tempted to have the head off anyway to inspect and measure everything, so as to eliminate a dark past, ie start from scratch, believe no one, and assume nothing.

 

[mr.change84]

Going back to basics, has the engine been compression tested? Can't see it in the previous logs.

No, not yet, because when we 1. got it going after timingbelt swap, it run so nice.. we think something else has developed

I'm sort of smelling a rat here, as in the damage is far worse than it was 'sold' with - ie a coverup to maximise saleability and profit.

car was sold "as is" with undiagnosed problem, expected we knew it had damaged belt.

You can have a guess what we paid for her

If the van drove absolutely fine before the belt failed, it's very unlikely to be anything to do with fuel supply or sensors. Normally its bent rods, compression, bent valves, snapped followers, and spun camshafts. I'd even be tempted to have the head off anyway to inspect and measure everything, so as to eliminate a dark past, ie start from scratch, believe no one, and assume nothing.

 

[mmi]

Perhaps you could make another log with a different logging setup below - as described in post #18

IDE00021 Engine RPM​

IDE00075 Vehicle speed​

IDE00086 Accelerator pedal position​

IDE00347 Air mass: actual value​

IDE07376 Intake manifold pressure: act. value calculated​

IDE07738 Charge air cooler inlet: pressure sensor 1 bank 1: raw value​

IDE07742 Cylinder head: pressure sensor 3 bank 1: raw value​

IDE09327 Cylinder 1 bank 1 internal moment​

IDE09328 Cylinder 2 bank 1 internal moment​

IDE09329 Cylinder 3 bank 1 internal moment​

IDE09330 Cylinder 4 bank 1 internal moment​

IDE10817 Lambda value at inlet of particulate filter​

1 minute idling in the beginning and 1 minute idling after the journey. Within journey a section of fairly steady speed (1 minute). And, of course, jerks and juddering (preferably with markers).

Trying to catch if there is imbalance between the cylinders, or poorly burned fuel (via lambda value possibly).

The values for cylinders internal moments saturate at well below max torque so would be most beneficial to have light foot.

PS. Don't forget to tick Group UDS requests - by 7

 

[St6]

Was map sensor in manifold gunked up when you removed it ?

 

[mr.change84]

Was map sensor in manifold gunked up when you removed it ?

Yes it was gunked up, but not crazy

 

[St6]

It could be your manifold is gunked up causing less air flow .i had this jerking few years ago and I replaced manifold and it sorted it