1.4TDi CUSB rough idle at cold start

[ellis8742]

Hi all,
Got a 1.4TDi CUSB 2015 VW polo, I know this isn't a Transporter but I figure there is a lot of common rail knowledge here!
I initially purchased the car as a non runner due to starting issues - turned out to be swarf contamination, changed HPFP, in-tank lift pump and injectors for refurbed units. Fuel tank and the fuel lines were all cleaned.
I've also rebuilt the engine as was low slightly low on compression due high mileage, piston rings head gasket etc replaced due to this. Pistons were in good condition, nil damage, connecting rods in good condition. On this side all is well.

It had an issue between replacing the fuel system and me rebuilding the engine - still has this issue, where on cold start (i.e when left overnight or for a period of time) the car will idle really rough, almost like a petrol misfire with RPM jumping between 800-1000rpm, this clears within around 1-2 minutes without throttle application and when fully warm doesn't present itself again. If the car is restarted when the engine is still 'warm' the idle is fine.

I've changed several sensors as part of the rebuild that i've done, fuel px sensor, crank sensor, cam sensor etc. The only thing I didn't change was the fuel px regulator on the end of the rail. I've pulled VCDS logs during a cold start and fuel pressure fluctuates quite highly during the initial cold start, this is accompanied by varying activation of the fuel pressure regulator.
I don't think this is an injector issue/isolated cylinder issue as all injector speeds during the cold start vary to the same degree, and all cylinder torque values are pretty much identical during the rough start indicating a potential issue across all cylinders.

I'm thinking this is a fuel pressure regulator issue just looking at the data but want to see if anyone else has experienced the same issues before I fire the parts cannon. Or if anyone has any further guesses as to what it may be..?

A few VCDS logs attached here, nil DTCs recorded.

thanks in advance!

 

[mmi]

Please post the following

1) Full VCDS Auto-Scan
2) Engine blockmap - Ignition ON/engine OFF
3) Engine blockmap - Engine running at idle
4) Engine blockmap - Engine running at idle - 3 minutes after startup


How-to create a blockmap file:

[VCDS]
[Applications]
[Controller Channel Map]
- Single Controller Address = 01
- Login or security access code: Leave blank
- Function: Measuring values
- Output: CSV file
[Go]

The result (TXT and CSV) files are saved into directory C:\Ross-Tech\VCDS\Logs
Please attach the files here.

---

all cylinder torque values are pretty much identical during the rough start indicating a potential issue across all cylinders.

I'd like to disagree - based on your log the "performance" of cylinder 2 is interfering with the rest

 

[ellis8742]

Thanks for your reply! I will capture these later on - also will do a data log with another cold start this evening.

Interesting, looking at the graphs again, I can now see that too. I wonder if this is due to erratic fuel pressure or potentially a dud injector…

Will get the blockmaps and link them here

 

[mmi]

CUSB engine has pressure sensor only in cylinder 2. It seems there is poor pressure build-up/poor combustion during the first 40 seconds.

 

[ellis8742]

@mmi see attached autoscan and blockmap files. Thank you for your help in advance!

 

[mmi]

@mmi see attached autoscan and blockmap files. Thank you for your help in advance!

Thank you! Helps a lot to understand what's available for monitoring.

I'm thinking this is a fuel pressure regulator issue just looking at the data

I would expect any issues in there to be seen across all cylinders. I think the fluctuations seen are because of ECU trying to stabilise the running.

I've also rebuilt the engine as was low slightly low on compression due high mileage, piston rings head gasket etc replaced due to this.

The issue manifesting itself only when cold possibly suggests a tiny leak somewhere which seals when things heat up (and expand). Possiblly injector seating, glow plug seating, even valve seating. Any audible chugging/puffing in engine bay?

Have you tried to maximise cylinder pressure when hot to see if there is "misfire" also then - high gear, start acccelerating at 1500 RPM (full throttle) (up to 2300 RPM). Preferably uphill to slow things down.

Perhaps you make a couple of logs with the setup below (please use the grouped UDS request!)

1) Cold engine start-up and idling 3 minutes​

2) A journey including the maximised cylinder pressure measurement (above)​

IDE00347 Air mass: actual value:​

IDE00589 Fuel pressure​

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

IDE07741 Cylinder head: pressure sensor 2 bank 1: raw value​

IDE07744 Particle filter: air pressure sensor 1 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​

ENG125966 HPV current demand coming from the IMV control​

ENG126008 IN_Injection_speed_injector[0]​

ENG126009 IN_Injection_speed_injector[1]​

ENG126010 IN_Injection_speed_injector[2]​

​

​

 

[ellis8742]

Thanks for the reply @mmi!
No audible chugging/puffing in engine bay during cold start, when I rebuilt the engine all injector seals were replaced, injector seats re-cut and new copper washers installed. Valve seats were re-lapped also along with replacement of valve stem seals.
I'll have a look at glow plug seating, will also test resistance of glow plugs - I did replace 1 and 3 as these had open circuit failures when I purchased the car.

Ref maximizing cylinder pressure - I did try this just after I rebuilt the engine to make sure all was well, I didn't perceive any noticeable 'misfire', although I wasn't data logging as such so I couldn't 100% confirm. It runs really smooth when its past this initial start problem when cold. Although will do it again just to make sure and also to capture the logs as suggested.

 

[ellis8742]

@mmi got a cold start log + 3 min idle and a driving log, this included some hill acceleration and some short acceleration bursts in 3rd gear, see attached.
Oddly, the cold start 'misfire' was less noticeable this morning, still manifested itself but not as noticeable in the cabin.

 

[mmi]

@mmi got a cold start log + 3 min idle and a driving log, this included some hill acceleration and some short acceleration bursts in 3rd gear, see attached.
Oddly, the cold start 'misfire' was less noticeable this morning, still manifested itself but not as noticeable in the cabin.

Thank you!
A kind of confirms a cylinder not playing along in the beginning. Cylinder 2 having lower torque spikes than the others.





It's interesting that engine running stabilises significantly after a short warm-up. Below RPM plotted at 0...50 seconds, and at 190...240 seconds.



As well as reported internal torques of all cylinders have stabilised

a driving log

A kind of expected - nothing obvious - e.g. no loss in cylinder pressure, etc.

 

[ellis8742]

Thanks for looking at those logs @mmi
Interesting, I’ll have a start with cylinder 2 looking at the data. Maybe I’ll send the injector for testing but then it doesn’t make sense how it quickly recovers and runs perfectly afterward…

 

[ellis8742]

Or potentially even the glow plug on its way out, still yet to check resistance itself

 

[mmi]

Maybe I’ll send the injector for testing but then it doesn’t make sense how it quickly recovers and runs perfectly afterward…

I'm not sure if testing would reveal anything as it's probably challenging to get the conditions correct for the issue.
What about just swapping (+coding) injectors 1 and 2 to see if the issue follows the injector 2?

 

[ellis8742]

@mmi been away for a few days and got round to swapping the injectors today, took a data log with another cold start after injector swap. Looks like cylinder 1 now has very low torque spikes after the swap - what do you make of the data

 

[mmi]

Hmmm... interesting. To me it looks like we now have both cylinders 1 and 2 performing poorly - cylinder 1 being slightly worse

---

The same data with a plot of 8-point moving average - emphasizes cylinder 1 difference​

 

[ellis8742]

Looks to be potentially injector related then
(??) comparing the data from the log before the Injector swap and now after I’ve swapped the injectors. Might send an email to the place I got them from as they’re still in warranty..

Also checked resistance of all glow plugs - all around 1 ohm so good on that side

 

[ellis8742]

Figured this out in the end... the 'refurbished and rebuilt' injectors that I purchased to cure the originating contaminated fuel issue were in-fact, not refurbished. They were old injectors that had just been polished/painted and a random injector adaptation code adhered to the injector - lesson learned I guess. Purchased another set of injectors and the car is running perfectly.
thanks for your help @mmi much appreciated.

to others, I would recommend avoid purchasing from WTdiesel..

 

[Bav]

to others, I would recommend avoid purchasing from WTdiesel..

You might want to consider posting a review for them, here...

Review A Business

Share the experience you had dealing with companies

www.t6forum.com

 

[mmi]

Figured this out in the end...

Excellent
Any healthy logs to share

 

[ellis8742]

Excellent View attachment 317297
Any healthy logs to share

To be fair I completely forgot to pull a log when I changed to the new injectors - was just happy to finally have it sorted!
Will try and pull a log if I remember later today!

 

[ellis8742]

Excellent View attachment 317297
Any healthy logs to share

See attached! For some reason there are two sets of data on that CSV file - both just copies of the data. This is a cold start + around 2 min idle. Cylinder torque now nice and smooth on cold starts with no massive deflections!