Recieved error code p0299 on my Skoda Octavia TDI with 170hp BMN engine. The code stands for that I get for a little boost and the car sets limp mode.

 

The code will come up at any time and very often regardless of how hard or normally I drive ..

Have had problems with stuttering at 3000rpm during hard acceleration and received the code for overboost which I solved by cleaning the VNT part of The turbo and thus it is after that problem was solved I got the above problem with underboost..

 

Have tried to change N75 valve and clean the map sensor, but it has not helped. I have also checked the vaccum hoses visually.

 

Has also logged boost with Autocom and it looks undeniably slightly wrong.

 

 

To the left is the curve I get now and to the right is the curve I got when I had problems with stutter (I have no curve to look at from when the car went well).

Both runs I started on third gear and 1000rpm and gave full throttle, at just over 3000rpm will the boost pressure peak that I can feel when driving as well but as one can see  I should have significantly higher boost pressure before. At 2000rpm.

 

The question is can it be map sensor is malfunctioning, even though I cleaned it? Or is there something else I should check out? Can add that I have runned with leaking EGR cooler for a while so was quite a lot of water in the intake pipe of the intercooler and there is where the map sensor is located , therefore I am a little suspious that it can be a problem with map sensor.

Egr are now plugged but not  reprogrammed can add that the intake manifold is replaced to one without the infamous troublesome swirl flaps.

 

On the picture with the test with autocom the two top curves stands for actuall boost pressure, The two in the middle are for requested boost pressure and the bottom curves are for engine rpms..

These can be tricky to get to the bottom of. Certainly that graph is very low on actual boost until very end of cycle range.

 

Does the car actually feel very sluggish and down in power / torque below 4,000 rpm?

 

You have replaced N75, have you tried checking moving / freeing the wastegate actuator, vacuum leaks to actuator?

 

Vacuum leaks to the actuator you can only really do visually by tracing back lines unless you have a vacuum pump or take it to a garage to get them to eliminate.

 

Could also be a diverter valve not holding boost but achieving boost at end of cycle may exclude that.

 

A boost pipe leak of that size would be audible with your window down I would of thought from the hissing sound.

 

You have cleaned the MAP but I suppose you could replace (although, given the actual boost readings are climbing, eventually,  I doubt that is it).

 

There is quite a few related threads around - I'll try and link a few.

 

I had that recently. One major issue was the actuator on top of the turbo. Replaced the actuator and it stopped going into limp mode.

Still had low boost until 2500rpm then normal boost and acceleration.

It seems the EGR was clogged a bit and causing excess smoke which clogged the turbo and the DPF.

Had to get the EGR cleaned and also the DPF cleaned out and the turbo refurbished.

Before it started going into limp mode the only thing that happened was it tried to do a DPF Regen every week. We should have got the EGR and DPF checked at that stage.

 

9 hours ago, TheClient said:

These can be tricky to get to the bottom of. Certainly that graph is very low on actual boost until very end of cycle range.

 

Does the car actually feel very sluggish and down in power / torque below 4,000 rpm?

 

You have replaced N75, have you tried checking moving / freeing the wastegate actuator, vacuum leaks to actuator?

 

Vacuum leaks to the actuator you can only really do visually by tracing back lines unless you have a vacuum pump or take it to a garage to get them to eliminate.

 

Could also be a diverter valve not holding boost but achieving boost at end of cycle may exclude that.

 

A boost pipe leak of that size would be audible with your window down I would of thought from the hissing sound.

 

You have cleaned the MAP but I suppose you could replace (although, given the actual boost readings are climbing, eventually,  I doubt that is it).

 

There is quite a few related threads around - I'll try and link a few.

 

 

It feels low on power until around 2500rpm then it explodes with power,   can't remember if it was like that when everything was working..

 

The wastegate actuator moves freely but with it dissconected from the arm on the turbo, the arm on the turbo drops down longer then the wastegate actuator can push it down, don't know if it should be like that?

 

I have also now changed every vaccum line without any results..

 

Diverter valve? Does that exist on a diesel?

 

Thanks for the links but seems like no one have had the exactly same problem as I and resolved it :/

25 minutes ago, FatblokeVRS said:

I had that recently. One major issue was the actuator on top of the turbo. Replaced the actuator and it stopped going into limp mode.

Still had low boost until 2500rpm then normal boost and acceleration.

It seems the EGR was clogged a bit and causing excess smoke which clogged the turbo and the DPF.

Had to get the EGR cleaned and also the DPF cleaned out and the turbo refurbished.

Before it started going into limp mode the only thing that happened was it tried to do a DPF Regen every week. We should have got the EGR and DPF checked at that stage.

 

 

Okay maybe I should try finding a better used wastegate (the actuator you're talking about) and replace that.

 

The egr valve I know is tottaly clean beacuse I have plugged it and I thankfully havent had any issues with DPF regens, yet..

1 hour ago, Backman94 said:

 

It feels low on power until around 2500rpm then it explodes with power,   can't remember if it was like that when everything was working..

 

The wastegate actuator moves freely but with it dissconected from the arm on the turbo, the arm on the turbo drops down longer then the wastegate actuator can push it down, don't know if it should be like that?

 

I have also now changed every vaccum line without any results..

 

Diverter valve? Does that exist on a diesel?

 

Thanks for the links but seems like no one have had the exactly same problem as I and resolved it :/

Yea,  you are right tdi - so no diverter valve on a diesel.

 

Does the wastegate arm on the turbo move through movement ok as well as the actuator?  If the pushing direction is the direction of the wastegate opening (releasing boost), which it would normally be from my recollection,  it doesn't surprise me that the actuator doesn't have total "full movement" (of the wastegate arm) it may not need to ever open to that extreme to regulate boost satisfactorily.

 

However, that does remind me of another recent thread in the last few months on a mk2 2.0tdi.  The turbo had been rebuilt / or replaced and boost and driveability still remained issues. Despite several attempts to reset the actuator and check vacuum lines etc. etc. in the end the turbo and actuator had to be sent for specialist bench set up, which solved the issues.  It surprised me that they were that sensitive to set up and even experienced mechanics could not get it right without specialist bench set up.

 

Edited 27 February, 20179 yr by TheClient