Audi A4 2.0 TDI Rough idle

Hi all.

Im currently involved with a 2010 Audi a4 with first generation common rail 2.0t tdi engine with piezo injectors
Car starts and drives perfectly.



Here a link to how a video showing how it idles
https://youtu.be/LTTMD0nzMdo

If I reset the inlet metering valve adaptation it will idle perfect for a few weeks depending on amount of driving, like so
https://youtu.be/LCayKYgUzOc

I have been told the fuel filter and inlet metering valve have been replaced and both items do look fresh.

No faults stored but watching measuring value blocks I can see rail pressure fluctuating wildly.
After resetting inlet metering valve adaptation it is perfect and injector correction values are perfect.
A leak off test of the injectors shows no problems.
Supply pressure and flow to the high pressure pump is good.
No TPI or any mention of a software update found on Audi Erwin

Supply to the inlet metering valve and rail pressure control valve are ok and supply and ground of the rail pressure sensor aswel

I attached a capture of it idling before and after IMV reset and the rail pressure can bee seen rising and dropping off repetitively before and its spot on after.

I have no comparison vehicle at the moment but everything looks normal after the reset.
theirs also a captures to see how it responds when the inlet metering valve is disconnected and reconnected.


Anyone come across anything like this before?or anyhting they think that might be worth scoping?
Tomorrow ill have a pressure gauge with me the check the pressure in the injector return line but im leaning towards a problem with supply to the high pressure pump or the pump itself but finding it hard to condem it with the way the car starts and drives

Have a look in measured values for Exhaust Gas Temp. there may be a calculated reading even if it is not fiited with a sensor.

What is the Engine Code ?

The videos wont help as much as a CKP / inj 1 trace on a ps data file.

Hi there

First of all - check for air bubbles in the supply line to inlet metering valve (IMV) and secondly check the correlation between the air mass sensor and the voltage signal from the rail pressure sensor.

Regards
Kim

Thanks for the replies.

Car is out of the garage at the moment but when its back in ill do as suggested and som more.

Had another look at this today as after 200 miles of driving .

Some more Details
Engine code is CAGA
No bubbles in supply to IMV.
Checked the pressure in the return line, result 8.2 bar specified 10 bar.(Dont feel this is a problem but have the pressure control valve ordered)
Changed the maths channels to get them matching live data % for inlet metering valve and rail pressure control.
Checked Exhaust gas temperature values as suggested and their all reading as expected
File with injector 1 and CKP uploaded with at frequency maths channel for RPM(Any way of smoothing this or is it less useful than an inductive type one for cylinder contribution analysis?)

Disconnecting inlet metering valve while running seems to have no effect at idle and but does under full throttle,no load condition.

@Kim
Just a question on checking the correlation between air mass and rail pressure sensor voltage?
I haven't been able to figure out a reason for this check? the vehicle will idle the same with the air mass meter and/or egr valve disconnected and the actual air mass value displayed was a plausible one taking into engine rpm variation.
Is it trying to establish if Egr valve is stuck open or opening itself?


I leaning towards another faulty inlet metering valve based on what im observing but im open to correction as I think their may be a problem with the rail pressure control valve at the same time





Should I be concerned with the upward slope while the inlet metering valve is being actuated?at the moment im not...
When back at work ill check to see if I have the same sign of circuit resistance and the engine control unit plug connection and decide after that

Notice the control values after resetting with VCDS


Its idling perfectly until with this amount of control

I do find it strange that the car will drive perfect while cruising and at full throttle.
Hopefully another one or something with same engine and fuel system arrives at work to gather some comparison values next week.

Cheers all

Hi Dieseljohnny

I think you are right in respect to a bad or sticking rail pressure control valve (DRV).

Seen at the start of this picture is it clear that there are some pressure in the rail.
A rail pressure sensor output voltage at 1.015 volt means there pressure inside the rail
and that is before the engine is even running. There should be a output voltage at 0,5 volt at
the rail pressure sensor with key on engine off which is equals zero bar of pressure.



There should be a direct correlation between the RPS sensor and the air mass sensor output voltage.
With a increased airflow through the engine the rail pressure should also rise.
The rail pressure are not a static value as you have observed.

If for example you have you have a air leak somewhere in the intake system or air mass sensor sending
faulty information to the ECU - the common rail system will see these correction and tries to correct
the duty cycle to the DRV and IMV with result of a lower pressure the the rail.

Can this the system produce maximum pressure ?

There are alot of questions one could ask about - but I would not do that.

Try to focus at one thing at a time.

Regads
Kim

Hello,
Bosch systems use both DRV and IMV controls depending on temperature and load of engine.
For sticking valves the current monitoring is important,use a clampmeter for PRV.
Also make a dynamic check the injectors only back leak test will not tell all the truth about the injectors and the compensation values is useless at piezo injectors
Regards...

Well after getting a run of these same symptoms in Audi and Skodas over the last few weeks.

All three with the same control system and piezo injectors just different power outputs doing the same thing.
Rough idle and rail pressure out of consistent control.

The DRV has been replaced on all three and all are fine after driving for awhile and getting feedback.
All DRV had the part number 057 130 764 H / 0 281 002 859

Just to note with the fuel temperature sensor disconnected all these managed to get rail pressure under control and idle perfectly.

I have had this on the same engine in a VW Sharan, it came down to either the IMV on the pump or the DRV on the rail and was difficult to prove either beyond doubt.

I used a PWM emulator in place of the DRV (First you have to place a load resistor on the DRV disconnected wiring connector to stop it raising a fault code) I adjusted the PWM duty to the DRV (with a view to hold it steady in different positions) and the IMV was able to control Rail Pressure very accurately with reference to specified on the scantool.

Then the other way round with the emulator on the IMV, adjusting the duty cycle either side of 50%, this time the DRV was incapable of maintaining steady pressure at any Duty but wildly fluctuating either side of specified.

That then made it clear that the fault was in the rail and not at the pump end. - Same fault, symptom & cure as yours !

http://www.ebay.co.uk/itm/Motor-Speed-C ... SwDuJWvFZ2

Ideal for testing almost every PWM controlled actuator we come across.

I have been looking in the past for some type of PWM actuator like the one you use in this case. Thanks for showing this, I will probably buy one by the way

But with this particular one you point, you only have control on duty cycle and not frequency right?
Isn't frequency an issue? Just asking...