Ml 270cdi turbo boost control

[Dragonml]

Hi
Can i ask for some help please.
I am trying to sort out 270cdi ml.
It has turbo boost control issue.
After the drive it will go in to limp mode.
Turbo boost control.
I fitted new maf pieburg from euro car parts,old one wasent showing any faults.
Still same.
Vacuum has been checked and its good at both egt and turbo side. Not droping vacuum at revs etc.
I got 2 more turbo/egr transducers and tried using them,still dose same. 2 spare ones i got are black rubber,on mine one is black one is blue,but i swaped egr and turbo and dident take notice of what color was fitted at turbo,blue one is different part number to black ones.
Turbo vanes are not stuck as i can manualy move the arm .
Turbo vacuum capsule is holding vacuum and not droping it.
I removed both catalytic converters.
Still same.
Inlet manifold flaps are knacked and need doing ,motor is still good as it moves when engine is reved up.
I removed broken linkages.
Wires to turbo transducer are good not broken.
Turbo transducer moves turbo control capsule fine.?
What else i could try?
I got spare turbo vnt control arm in good working order but one on the car seems good.
Any ideas please

When it happens .stop turn key off restart and its good again,it puzzles me.
Had gearbox fluid changed today and its good and at correct level.
Thank tou

 

[Uncle Benz]

Have you checked the boost pressure sensor? It's in the pipe after the intercooler iirc. Could be the turbo is all working correctly, but the sensor measuring the actual boost is faulty. Sounds like you have checked the turbo and associated gubbins pretty thoroughly

 

[oigle]

A split boost hose or similar will give same results. Loss of air mass upsets the system and sends into limp. Check hoses, intercooler etc for any leaks.

Ian.

 

[Dragonml]

Hi
Thanks for replying
I have just neen to friend of mine who has merc-star diagnostic.

I wanted to check gearbox to make sure its good and no faults.

He cheked engine codes etc.
It came up with
P1470-016 fault code.
Charger pressure control positive control variation (charger pressure to low)
My delphi diagnostic was just giving fault code p1470 as turbo control.
So i know its lacking boost some how.
I will check intercooler (no leakes can be felt and no oil seepage anywhere)?
Will check all intercooler pipes
I will take pressure sensor out and cleen it.
I will have to do manifold flaps too.
Try all 4 turbo transducers and see how it behaves.
Turbo it self spins nice and free minimal play,check it all when i had cat off.
Vanes on the turbo are not stuck move free by hand.
If after it all is same dont know what to try?
Swap turbo,fit different turbo vacuum capsule i got as spare?
Thank you for help .

 

[Dragonml]

I never had issues with low boost on any other cars i had and worked on mainly vw audi tdis with vnt turbos.
It was always turbo pressure higher than requesting due to vnt turbo sticking

 

[Westheath]

If the VNT arm moves 10-12mm without snagging or sticking, check the impeller spindle for excessive play.

There must be little to no play as these can momentarily stick when hot causing limp mode to kick in.

And ensure all pipe work is isn't leaking including anything vacuum related.

 

[Steve@Avantgarde]

Charge pressure too low...it has an air leak....

Have you carried out a charge pressure test (tests to see if the turbo system is air tight)? If not I would recommend you do so. Then carry out a smoke test to see where the leak is coming from.

Its usually the top hose to the manifold...splits on the underside so you don't always see it.

But I would stop guessing and throwing bits at it until you do some solid diagnosis....

 

[Dragonml]

Just to update
Boost pressure issue was down to inlet manifild flaps.
2 out of 5 were gone and i got them out, stuck next to inlet valve.
Holes were open on manifold were pivot arm rod is.
All well now no more limp mode.

 

[rayofsunshine]

If the VNT arm moves 10-12mm without snagging or sticking, check the impeller spindle for excessive play.

There must be little to no play as these can momentarily stick when hot causing limp mode to kick in.

And ensure all pipe work is isn't leaking including anything vacuum related.

Spot on Westheath and Dragonml
With all other avenues covered and symptoms as above I removed the Turbo dismantled and installed a new cartridge, what a difference, my ML now behaves like a Merc should.
Thanks to all
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