Technical Boost contol valve vacuum.

[gork]

I have a 2013 Ducato Multijet 150 with the well known P0238-61 error code.
I'm trying to understand function of boost control. On engines where waste gate was controlled by pressure, it was easy. Increased pressure means more opening on waste gate.
But on a 2.3 multijet the boost is controlled by vacuum.
My question is.. Is the wastegate opening (reduce boost pressure) with higher vacuum ?
Or is it opposite ?
I have read on forum, but have not found anything.
I have searced on internet and also this forum, but have not found anything about this.
I know about MAP and boost control solenoid..

 

[Anthony489]

Hi gork

This is my understanding, which I am 95% confident of ( Never 100 % !)

DTC P0238-61 is listed as "Turbocharger control positive drift (Low Pressure) - Signal calculation failure"

This engine has a variable geometry turbo (VNT) with multiple hinged vanes. They are all opened and closed together via a rod from the vacuum actuator. With high vacuum, the rod moves towards the actuator and the vanes close (low boost). With low vacuum (or vacuum hose pulled off) the rod moves towards the turbo and the vanes open (high boost). See pictures from Garrett.

The vacuum actuator also has an electronic position sensor, which feeds back to the ECU via 3 wires so that it "knows" the position of the rod.

I suggest you check:

Free movement of the vanes with the rod disconnected - are they sticking ?
Connector and 3 wires to the ECU all OK ?

One more check - is the wiring to the ECU OK, no chafing of the loom near the ABS brake unit ? See this story for more details: https://www.picoauto.com/library/ca...th-turbo-under-boost-and-air-flow-meter-drift

 

[gork]

Thanks Anthony for reply, suggestion on fault tracing, and also link.
What i read in that link you sent he says. "... so at around 70% operation the vacuum to the turbo was too low so it would under-boost."
This sentence i understand as low vacuum means low boost pressure. But that is opposite to what you write.
"With high vacuum, the rod moves towards the actuator and the vanes close (low boost)."

(Low vacuum means close to atm pressure. High vacuum means lower pressure than atm pressure. Or is it opposite?? )
That's why i'm confused..

I would have thought that for fail safe, increased vacuum means high boost pressure. No vacuum means no boost. That way there will be no risk of overboost.
When i connect Multiecuscan it is reading Boost Pressure: 536 mbar, while Desired Boost Pressure: 980mbar. Atm pressure: 1009 mbar. And Turbo Actuator command: 64,77%

 

[Anthony489]

Hi

I agree that it makes sense that no vacuum gives low boost (=failsafe), so it is most likely the opposite way round to what I said - apologies !

I did say 95% confident

Yes, high vacuum means lower than atmospheric pressure.

With atmospheric pressure of 1009 millibar and boost of 980 mbar the manifold absolute pressure (MAP) will be 1989 mbar, which will be reported by the MAP sensor to the ECU.

I don't know the maximum boost for this engine, I estimate 1500 mbar giving a maximum MAP of about 2500 mbar.

Your 64,77 % command sounds reasonably high. Are you able to read the feedback signal from the position sensor ?

The reported boost pressure is too low. This might be a problem with the Turbo/Turbo actuator, but it is also possible that the MAP sensor or its wiring is under reading. Have you cleaned/changed the MAP sensor ?

 

[gork]

Vacuum is always confusing. So it is good to get it sorted.
For me these values does not tell me too much, as i don't know what to expect at different levels.

Boost pressure signal: 0,9491V
Actual Turbo control positon: 1,453mm
Desired Turbo control positon 1,415mm

I also know that EGR is blanked on this engine.
Engine code: F1AE3481E

The MAP sensor is new, and also boost solenoid. All vacuum hoses are cheked, and ok.. Also checked the hose to turbo actuator, and it holds vacuum ok..

 

[gork]

Was out a short trip.. Started with cold engine.. After a few km, i got engine warning light, and loose power. Engine Temp 67 Deg. C. See freeze frame.. I only had my hand held diag tool with me this time. I stopped to save freeze frame, and reset error. Continued driving 30 km, and engine is working fine. Good response on pedal. No more errors.. There is a sound coming from engine when pedal is around "neutral" while driving. If i hold speed theres no sound. If i press just a tiny bit it makes sound, but if io continue lower pedal, there's no sound. And same if i release pedal a little. Trottle housing is replaced after egr blanking, so it is clean. Turbo was replaced 2 yrs ago by a fiat workshop.
The datastream picture is taken while driving after error code reset.
From what i can see, the boost pressure is normal..

 

[gork]

Today i did a small test today with my hand logger connected. Luckily i did look at the display when i got error.. For a little second, i saw that MAP pressure did read 0, and the engine light came on..
Engine temp. ca. 45 deg. C. I did reset the error code and continued driving. No more error occured.. It seems like it is only happening when engine is cold. After heat up, it is working normal.. Anyone have an idea to what can be the problem ? I will connect Multiecuscan and do a logging of parameters.

 

[Anthony489]

Hi again gork

The MAP sensor / Temperature sensor is wired directly to the ECU, with 4 wires, Power, Ground, MAP output and Temperature output. Low manifold pressure gives a low output voltage (see graph).

If the reading suddenly goes to zero, it could indicate an intermittent problem with the MAP connector, the ECU connector or the wiring loom in between.

 

[gork]

Hi Antony. Thanks for reply.. I thought about intermittent problem so i will check wiring. The weird thing is that it only happens before engine is warm.. After normal temp, the error do not show up, and I did not see Zero reading on MAP after error reset..

As i said, i will connect MES later today and log data while driving..

 

[gork]

Did a test with MES today and got the fault logged. After engine is at normal temp the error does not apply again after clear code.. Unfortunately i forgot to log engine temp.. Screenshot is where error applies. There was some noise from engine when error occured. Guess it is vacuum actuator. It is same noise that i can hear when i drive if i move pedal a tiny bit up or down.
Maybe i should have logged othet parameters too? Problem is that i have to wait until engine cold befor i do new test.. Will take a new tomorrow again. What parameters should i choose to trace ?

 

[Anthony489]

Hi gork

I have looked at your screenshot. Here are my observations:

201 to 206 100% acceleration with RPM rising (I assume)
206 to 208 Lift off Gas Pedal
208 to 214 100% acceleration, RPM rising more slowly (higher gear ?)
214 to 216 Lift off
216 to 222 66% acceleration
222 Sudden Event - Change in behaviour
234 to 236 Lift off
etc

Gas Pedal Position % follows Gas Pedal Track 1 Voltage 3.5 V = 100% Looks OK
Throttle Valve is mostly nearly fully open (Trace is inverted), slightly closed for 66% accelerate, open after Event. Looks OK
Boost Pressure and Boost Pressure Signal follow each other. Looks OK
Boost Pressure follows Desired Boost during 100% acceleration , but is too low during 66%. Even lower after Event
Actual Turbo Control Position follows Desired until Event, then rises to 11.05 mm (Vanes Fully Open) and stays there
Desired Turbo Control Position ramps up as RPM and airflow rises, during first 100% acceleration Looks OK
Turbo actuator command is inverted compared to actual Turbo Control Position. At Event, command goes to zero (= vanes fully open) even though the desired Turbo Control Position is very low

I suspect that the "Event" is software intervention to turn on "Reduced Power / Failsafe Mode". Maybe the turbo vanes are fully opened for this mode. I suggest you concentrate on the question "Why is the boost lower than desired at 66% throttle (216 seconds onwards) ?

As you know, the ECU drives a solenoid valve. This valve varies the vacuum applied to the Turbo actuator, to control the vane position. The vacuum to the solenoid comes from the engine vacuum pump (the one that runs the brake servo) via a small rubber hose. The variable vacuum goes from the solenoid valve to the turbo via another small rubber hose. Check these hoses carefully for splits, loose ends etc.

What error code was logged for this test ?

 

[gork]

Anthony. Thanks for quick reply and analyze..
From txt log file..
READING ERROR CODES:
1. P0238-61 - Turbo pressure
ERROR DETAILS:
Operating time: 52405 min
Engine speed: 2099 rpm
Engine temperature: 70,00 °C
Battery voltage: 14,269 V
Total fuel quantity: 62,118 mm³/i
Intake air quantity: 940,0 mg/i
Atmospheric pressure: 1003 mbar
Boost pressure: 1689 mbar
Desired boost pressure: 2313 mbar
Actual turbo control position: 0,810 mm
Desired turbo control position: 0,818 mm
Actual EGR position: 5,457 mm
Throttle valve opening: 82,94 %
Air temperature (Boost/Manifold): 41,50 °C
Air temperature (MAF): 20,00 °C

 

[gork]

Forgot this. Sorry..
I have checked the the hose. They are all fine. Also vacuum hosefrom engine is fine. The hose from solenoid to turbo tubing is ok. Need to check the small hose between tubing and turbo, but i think it is ok..

 

[gork]

"Why is the boost lower than desired at 66% throttle (216 seconds onwards) ?"
This is when i hear the noise coming from engine. Guess it is the boost actuator. I did hear the noise, and then i held pedal steady to see what is happening. I then get error and engine looses power.. The weird thing is that it happens before engine has reached normal temp. This time 70 deg.C. In my first test with handheld code reader 67 deg.C. If i clear error i can continue drive, and engine is like normal.. Attached file is after i cleared error.. I still can hear noise if i push or release pedal very little. This is only when i hold pedal to hold constant speed. I see from the attached file that boost pressure is too low.. Could it be wrong adjustmet of rod lengte on turbo actuator so it is not closing as i should ?

 

[Anthony489]

Hi

The idea of the variable exhaust vanes is that they partly close at low RPM/low throttle to increase turbine speed and boost, then open at high RPM to avoid overboost. There is no separate wastegate.

I believe that the actuator is supposed to be calibrated/adjusted in some way to match the turbo. I don't know how critical this setting is. If you have not enough boost at low or part throttle, I agree that it is possible the vanes are not quite closing enough. The system of feedback means that the rod is being set to the desired position (in mm), but maybe this doesn't correspond to the correct vane opening ?

Are you able to detach the actuator and move the turbo vane mechanism by hand, to check that it is moving freely ?

 

[gork]

Hi
My next plan is to have a look at this. But unfortunately i do not have the time today. Will try to do it as soon as possible.. Thanks..
The turbo was replaced 2 yrs ago. I was not the owner og this car then.. last year he had complaint about noise from turbo, and also Check Engine light. The workshop took the car in for check, and work report says something like reset error and "adjust" something (don't remember.need to look in papers. Sorry.) Then they had a test drive and found everything ok.. Well. If engine is warm and they reset error, and then do a test drive, the error wil not show up until engine has been cold. I will not say that this workshop impress me.
Will try to detach actuator and try to move turbo vane when i got time. Hopefully tomorrow.

 

[gork]

Did have a look at the turbo, and all seems to be correct. Discussed with my son and, I think we found the problem. I bought this car i July so it is quite new to me.
As mentioned earlier, there are egr blanking on this engine from previous owner. The EGR is not removed from ECU software, so ECU still expecting normal function. Which is not happening with a blanking plate.. I removed the blanking plate and took a test drive. Everything was working as normal.. No error, and no noise from engine.. Boost pressure also seems normal. Data is from test today..

 

[gork]

Forgot to add engine temp.. This picture have temp added, and you ca see EGR starts working.

 

[Anthony489]

Hi

I am glad you seem to have finally found the problem. The EGR system is most active under light load conditions. By removing the EGR but not changing the software, it's possible that the Throttle Body was being closed too much and starving the engine of air.

 

[gork]

Hi.. Yes it sounds reasonable.. I will have my car on MOT ? check next monday so i hope all is fine now.
Edit: I guess the noise came from trottle body that did close and open quickly..
And thanks for help Anthony.