Some strange boost problem

[evoms_gti]

Hi guys Im new here, however Ive been experiencing a very annoying problem. Since Im not so experienced with these motors Im hoping someone might shed some light or direct to the correct path to solving this problem.

I have the 2.0TFSI k03 lump with basically ALL supporting mods and custom ECU tuning to a what i would call a stage 2++ (with an extra plus on there because im over 285bhp)

Right the symptom is this: anywhere between 5200rpm and 6200rpm in ONLY 3rd or 4th gear I get an extreme boost drop and then a rise again. I know its normal for the boost to taper off as i go up the revs but to drop from 15-16psi to 8psi and then to rise to 13psi again seems quite strange to me. The extremity of the drop depends on the rpm that it happens if its higher up the revs then the drop is less extreme

I get the feeling that its the wastegate opening and closing again for some reason! I have changed the cam follower but nothing, we are also trying to catch the problem on data-logging but it hasnt done it so far while its connected to the laptop.

What i plan to do is change the intake cam as it wasnt changed with the newer harded alloyed cam that was in the recall and also add S3 injectors as my tuners suspicion is that its a fuelling problem.

Its really getting me frustrated as it wont let me enjoy the pull and the torque of the car :(.

Can anyone help? Has anyone had something similar?

Thanks in advance

PS: the car boosts normally to full boost so its not a leak problem  

[edd666999]

any extra high pitched screeches when on boost? You might think its the intake noise

[evoms_gti]

hmm there is something like a high pitch sound-whistle of the turbo keeping in boost! this sound is audible once the boost starts tapering after around 5000rpm. once the problems occurs boost drops and that sound stops

thats the best i can do to explain it unfortunately but there is some kind of sound i can hear slightly for sure. its not very audible though

also forgot to mention that the car has thrown some faults too. most with the first oxygen sensor showing 'too lean' and another about the flaps in the intake manifold. what is strange is that the problem doesnt occur when the car is in full boost when supposedly the car should most logically be running lean! it does it when the boost tapers off 

and thanks for the reply

[evoms_gti]

Anyone anything please. At a dead end here

[evoms_gti]

Sorry to bring this up again but any kind of idea suggestion or suspision would be a great help at this point!

Has anyone experienced anything similar?

[Hedge]

It sounds like you're running out of fuel.

Get your tuner (you don't mention who) to log the car, specifically the blocks relating to fuel pressure.

[john87]

DV leaking?

[evoms_gti]

It sounds like you're running out of fuel.

Get your tuner (you don't mention who) to log the car, specifically the blocks relating to fuel pressure.

thanks for the reply, I was hoping that someone verified that this is a symptom of fuel lack as Im not experienced with turbo cars which occasionally suffer from this problem. I dont know how 'lack of fuel feels' and how the TFSi engine reacts to this.

after eliminating other possible faults we too came to a rough conclusion that its something to do with fueling! there is no point mentioning who as im from Cyprus which means it doenst affect most members on here.

like you said our next mission is to log fuel pressure to verify that it is indeed fuelling thats causing this! Ido have the autotech uprated internals however I havent got the S3 injectors which are in my future plans.

[rich83]

As Hedge says.... it sounds like you are getting a fuel cut or fuel deficiency. Is it really "hard" boost cut... akin to taping the brakes quite hard?

[evoms_gti]

DV leaking?

the DV actually opening up for some unknown reason was one of our initial thoughts but we eliminated this as the boost drop wasnt instantaneous but rather gradual  and very swift which might imply that its probably the wastegate.

Im not convinced its Dv leak as the actual boost always meets requested boost on the logs and boost level are consistent too.

On another thought could this problem have anything to do with the N75 valve or the N249? VCDS hasnt shown a fault with these valves

[evoms_gti]

As Hedge says.... it sounds like you are getting a fuel cut or fuel deficiency. Is it really "hard" boost cut... akin to taping the brakes quite hard?

its a gradual but very quick drop from whichever boost it is to somewhere around 8psi and then back up to the correct boost of the rpm the engine is in.

it doesnt feel quite as much as hitting the brakes to be honest mate! its more like letting off the accelerator petal even though Im stepping fully on it.

like i said though this has never happend on full boost but anywhere after 5200rpm when the boost is actually tapering off

[evoms_gti]

Why?

I guess some of you will be asking why have I decided to install an uprated HPFP at stage 1 as it is usually installed at the same time as stage 2+.....

As most of you probably know I do a lot of logging my car with VCDS.  As part of the logging I noticed that even while the car is at stage 1 an uprated HPFP would be of great benefit. A picture says a thousand words so here you will see what I mean:

Here is a rail pressure plot of what happened with B7 on the OEM HPFP:


Here is a rail pressure plot of B7 with the Autotech HPFP:


As you can see the OEM HPFP is simply not able to maintain the requested rail pressure at B7 while the Autotech HPFP keeps up with no problems at all.  This is why I have always run my stage 1 map at B6 up until now.  When running higher boost it puts more pressure on the HPFP to provide fuel.  This is because higher boost = higher airflow and to maintain AFR if you are flowing more air you will also need more fuel.

Before getting the upgraded pump fitted I wanted to make sure there would be no issues running the pump with stage 1.  After having spoken to JKM and REVO I learned this should be no problem at all.  Here is some great info I learned from JKM:

[evoms_gti]

^I have found this in the product review section and the initial plot showing the fuel pressure drops after 4500rpm does indeed support the idea that its a lack of fuel, however on the other hand I do have the same autotech HPFP so my car should be similar to the second plot! I really dont know what to make of this  

[stewart]

I could be totally off the mark here but I had a similar problem.

I got VW to change the spark plugs when it was in for a service and the problem disappeared. I didn't think it would have been the plugs, thought it must have been the n75 valve or DV from reading similar posts on here but I was wrong.

I'm no expert but it could be something you could try as it does sound similar.

Good luck getting it sorted.

[evoms_gti]

I could be totally off the mark here but I had a similar problem.

I got VW to change the spark plugs when it was in for a service and the problem disappeared. I didn't think it would have been the plugs, thought it must have been the n75 valve or DV from reading similar posts on here but I was wrong.

I'm no expert but it could be something you could try as it does sound similar.

Good luck getting it sorted.

ive recently changed them for iridium NGk ones not more than 6k miles ago! before going to stage2+ they were working fine but i shall give them a try you never know!  thanks for the reply