[SOLVED] Missing boost on 1.4Tdi 55kW

3dB

3dB

Member
Hello guys, I'm new here, hopefully someone can help me out. :)

Recently bought an A2 and now trying to sort its issues out. Car seems to have low power, quick check with VCDS shows up error code in boost regulation - negative deviance and Measurement groups (actual vs requested) seem to confirm that. So far I visually checked all exit piping from turbo to inlet manifold, all seems to be ok. Is there any way to check N75 for faults? How is correct lenght set on turbo wastgate actuator? (i'm kinda suspecting the actuator arm is too long, because engine has been tampered with before car got to me and I see fresh silicone sealant on turbo oil pipe return connection)
 
Have you checked the dead leg corrugated tube that goes along the radiator top all the width of the car ? mine have had cracks..
Maybe also check the turbo axle for play and that it spins nicely ?
 
Yesterday got time to tinker around a car. So I changed all the small hoses around the N75 for new ones, checked turbo for axis play and found it perfect, no play, cold part blades look ok. Checked again visually for intake hose breakage but still found nothing. Intercooler is also visually Ok. Today I will try to change N75 for a new one. All that remains is wastegate actuator leg shortening... Not looking forward to it at all, as turbo location on this car is a pain to work on. :(

a2 turbo.jpg
 
Had this issue across 2 different tdi A2's - loss of boost at 70mph especially uphill in the first and loss of boost around 90mph in current A2, gradient making no difference. The first was caused by a cambelt/waterpump change, which popped off one of the vacuum hoses at the back of the engine bay (access only from underneath I beleive). On this vehicle the issue was already present and I only took it up to just before 90mph on the test drive and didn't realise until months later. Very interested to see if you find a solution to this issue, it seems very common and very infuriating to pin down - expensive and often needless replacement of parts trying and failing to solve the problem. My money is on the small vacuum hoses opening up under pressure but are the N75 hoses you've replaced already the same as the vacuum hoses? Lots of posts on this issue over the years but I've never read about anyone completely fixing the problem. Good luck and please post as much info as you can if you solve the problem!
 
Wastegate turbo on AMF 55kW engine ar not regulated with vacuum (like 66kW ATL engine with VNT turbo), but with same pressure generated by turbo. N75 valve is basicly a solenoid switch, that switches one input to other, one being turbo pressure output and second being turbo air intake. As I understand, this done by varying duty cicles - fast switching between inputs, varying more open/close to one or other. Output is wastegate actuator, more pressure it gets, more wastegate is open, more exaust gas bypasses turbo. This wastegate actuator is also spring loaded, to keep wastegate shut. Theese N75 valves may be worn over time, so that's next in line for replacement, as I don't have known good one for test fitting. If replacement will do nothing, then actuator spring needs more tension - hence shorter actuator leg. I suspect actuator leg being too long, because before car got to me, there was some tampering done with the engine, maybe noob mechanics left it too long.

Those "vacuum" hoses are Ok, as I replaced them all yesterday.
 
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Changed N75, still no fix. Got another idea... Maybe EGR valve is not closing properly and I'm loosing boost in exaust. Is there any way with VCDS to disable EGR function? Looks like tomorrow is time for another car tinkering afternoon.
 
if its the AMF engine simple remove the vacuum pipe to the EGR valve this will disable the EGR and ECU is none the wiser
If its the BHC engine then same can be done but only as a test as the lack of EGR will throw a MIL light after a few miles

Cheers,
Paul
 
Always good to share engine code/year in such a thread since both AMF and BHC are 55kW.
Good to hear that your turbo is free of any play. (I looks close to new on your picture)

If I understand your issue right, it would be useful to verify whether your engine do not produce sufficient boost or if it produce boost but it leaks out somewhere in the loop....

If it was my engine... I would have pressure tested the aftercooler line. ( visual check is good but pressure testing is better...)
You can buy or make two plugs, fit one to the hose that is connected to air outlet side of turbo and one to the hose for inlet manifold.
I have M10x1 threads in one end that fit a boost manometer and a 5mm hole in the other plug where I connect a simple football pump.... and apply 1.4bar. If it says pzzzztttsss somewhere I spray water with soap until all pzzzz...places are lokated/fixed.

Next step for me would have been to attach my boost test gauge to the aftercooler line. My personnel opinion is to verify that there are too little pressure before starting to adjust actuator leg. (and if you adjust plz do attach a boost device so you can monitor boost)

Your VCDS is probably able to give you live data for boost. An ELM+ android/ iphone can as well.
 
Engine code is AMF.

Had idea of pressure testing boost pipes too, but I don't have anything to make this pressure or to seal off input end. Ether way, I visually checked all the piping, all looks good. Maybe turbo is changed, as it looks too clean, except actuator, that looks like 182000km driven used actuator should look.

I used VCDS for boost pressure monitoring, and actual vs requested is mostly about 50% off.
 
Our aftercoolers struggle with "end tank lift off" and general leakage. None of these errors can will be discovered by visual inspection. Pressure testing is to my opinion more or less the only way to achieve verification of a non-leaking system....
 
Well, it's not EGR. Took it off, cleaned all the gunk out and blocked it off. New seals and all. Still same results...

Egr-block solution is diy metal plate between two gaskets.

IMG_20180405_153649.jpg
 
Tinkered with the car a bit more. Checked the wastegate actuator and yes, actuator leg was set too long, shortened it but still no car fix. Took some more intake pressure logs, turns out, when you disable wastegate regulation (wastegate closed at all times), turbo can do 1.2 bars of pressure, but pressure is building up quite slow - hence non responsive car. Took off exhaust completely and did test drive, thinking maybe catalytic converter is blocked, nope, cat is fine, as no change in performance.

Found out one more thing, VCDS shows Torsion Value -4°KW on warm car. Some reading up on this matter (mainly on 1.9TDI PD engines) reveal, that low performance in low rev range could be attributed to this. At 1.9tdi pd engines, camshaft sprocket can be adjusted by loosening 3 bolts, maybe on 1.4 it is the same. Will try to tinker with that tomorrow.
 
Car is fixed and running really well now. :cool:

Turns out, it was bad injectors underfueling engine. Got them out, get them to injector guy for a test and yes, all three underfueling - no power for car. Only way to really test injectors, is to pull them out and put it on test stand. Bought some stand tested good ones and installed them this evening. Car runs great now! VCDS values are where they should be too. ;)

And for torsion value, according to engine manual, yes -4 is a bit out of spec, fixed it to 0°KW.
 
3dB said:
Car is fixed and running really well now. :cool:

Turns out, it was bad injectors underfueling engine. Got them out, get them to injector guy for a test and yes, all three underfueling - no power for car. Only way to really test injectors, is to pull them out and put it on test stand. Bought some stand tested good ones and installed them this evening. Car runs great now! VCDS values are where they should be too. ;)

And for torsion value, according to engine manual, yes -4 is a bit out of spec, fixed it to 0°KW.
Click to expand...
Always good to hear the solution, hope to never need it. :)
 
3dB said:
Car is fixed and running really well now. :cool:

Turns out, it was bad injectors underfueling engine. Got them out, get them to injector guy for a test and yes, all three underfueling - no power for car. Only way to really test injectors, is to pull them out and put it on test stand. Bought some stand tested good ones and installed them this evening. Car runs great now! VCDS values are where they should be too. ;)

And for torsion value, according to engine manual, yes -4 is a bit out of spec, fixed it to 0°KW.
Click to expand...

Fantastic news congratulations on solving the problem!
 
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