Hmm interesting, I did experience this in my old Lancer Evo 2 - fitted a 3" downpipe/decat caused boost creep at WOT.

Could it be that the ECU recognises the 'overboost' and adjusts/lowers it momentarily when it climbs again it lowers it again, so on and so forth - which gives the resultant 'pulsing'?? Just theorising here.

Could do with knowing whether different wastegates were used, and/or whether a weak/worn wastegate could cause these symptoms of boost creep also?

Thing is which makes me wonder, is that generally even on part throttle (not full boost) with lower boost it's hesitant and pulses slightly, which if it's not reaching peak boost can't be over boosting?

The only time I don't notice any symptoms is on light throttle/driving miss daisy mode .

Bit of reading for you here

AudiWorld Forums: About the N75 Wastegate Bypass Regulator Valve. (m)

and if you fancy reading 17 pages on similar problems

LEON CR fluttering boost problem - SEAT Cupra.net - the world's largest & most popular SEAT Forum

Nice find Martin - first link kinda confirms that if the car is getting too much boost, the ECU will alter the signal to the N75 which can result in surging which I assume will be this 'pulsing' I can feel?

Wonder with the increased 3" downpipe and decat, whether it's overboosting due to this - perhaps although the Map is set to 15/16 psi, it's hitting more and the ECU is trying to compensate? hmmm

Nice image showing the N75, N249, Diverter Valve and how it relates to boost control - it's nice to get an idea of how it works.

Do you have a registered copy of vag-com? as you will be able to log actual vs requested boost.

On the cars i have run logs on, the boost pretty much matches what is requested, it just seems to jump about a bit. I suppose there are many factors in each map/ car that could cause these symptoms fueling,timing, ecu corrections etc,etc.

Yep have a registered/licensed vagcom haven't logged any data before, is it simple enough to do? and which ones would I need to log?

Cheers

Engine- measuring blocks. block 115 is boost pressure. type 115 ,Click log, start and do a third gear run from low revs to 6k then clutch in and click stop.

ta, will try that tomorrow!

Right did some data logging today, boost and power/torque - did all runs on 3rd gear from low rpm through to 6.5 - 7k

All throughout it didn't seem to hesitate much :( on WOT - but nonetheless, I don't know if the boost is correct - also bhp seems low to me, which I can attribute to the torque curve not sustaining the peak for very long :(. Any observations? Do these look right? The torque seems erratic! :confused: Peak power was 206bhp and 231 lbft torque.

Stated power on a remap on a standard vRS is 212bhp according to chippeduk

Does seem strange the way the boost just drops off at around 5500 rpm..... very strange. Decats can also hamper performance imo due to lack of back pressure. I have seen some vrs with this map make a higher bhp figure than yours but saying that every cars different and chippeduks figures are only a guide.

Cheers - I was thinking the turbo is 91k old (still think it's the original) so perhaps wastegate is a bit weak, could be why the boost drops? Or perhaps there is a leak in the system somewhere - could be the cause of my hesitation.

Quite pleased with the torque figure, just a shame it couldn't hold it for longer to give me a better bhp figure, but again looking at where the torque drops with the boost drop - looks to be the cause of that.

Strange thing about the decat, all my previous Evo's have benefitted performance wise from this.

Cheers - I was thinking the turbo is 91k old (still think it's the original) so perhaps wastegate is a bit weak, could be why the boost drops? Or perhaps there is a leak in the system somewhere - could be the cause of my hesitation.

Quite pleased with the torque figure, just a shame it couldn't hold it for longer to give me a better bhp figure, but again looking at where the torque drops with the boost drop - looks to be the cause of that.

Strange thing about the decat, all my previous Evo's have benefitted performance wise from this.

The turbo looks to be working fine as the specified boost which is set by the ecu/map is followed nicely. So the ecu is requsting the boost to be dropped and the n75 is opened to hit the requested pressure (think thats how it works).

My money is still on the map being the problem.

I could not believe the difference between my 2 maps. Mine used to have the boost spike like yours then it used to drop off and cause the brief hesitation. Since new map i don't get the spike just smooth acceleration then it goes a bit more further up the rev range.

Not sure if this helps, but here's my boost logs for a stage 1 remap with APR

Your's seems to hold high boost then drop off, where as mine slowly decreases. Both end up about the same though, but mine at a guess would feel alot smoother.

cheers guys - I have relayed all info you have provided to the mappers - very useful!

Wow - haven't posted in a while.

Right well, I went to the mappers who spoke to ChippedUK, I had a more specific map applied (taking into account the decat/downpipe) map file size was quadruple the original map size, and it was better for about 100 miles, then slowly started noticing the hesitation/stuttering again - it no longer hesitates bang on 2500rpm and above as it did before, but does it higher up the rev range - it's still very noticeable :(

On Sunday I had the original downpipe/cat refitted, and hasn't affected it :( - so looks to be something in the map, or possibly a component that the increased demands of the remap is affecting?

I was wondering if a faulty/worn turbo actuator could cause it? Mine has done 93k miles so is well used. I wondered if it was weak and allowing the turbo to momentarily overboost, does the ecu have some way of recognising overboost and reducing it (giving you the constant hesitant/stuttering/inconsistent boost)

Grabbing at straws here I know

were have you got it mapped again mate?

have you tried goin back to the original map? that should tell you wether it is the car or the map.

I solved the problem on mine by buying a Focus St, now its sweet all the way:thumbup:

I solved the problem on mine by buying a Focus St, now its sweet all the way:thumbup:

What a brilliant suggestion

only buy a focus st if u like visiting fuel stations a lot,mate has got 1,has seen it down to 15mpg.

sorry if this has already been said. i havnt read the whole thread. this might be of interest to u tho.

i had my car mapped about a month ago, i hav'nt replaced the dv yet but the guy at mrc tuning told me if the dv goes.. buy an audi s3 one! apparently they are exactly the same but have a stronger diaphragm and a stronger spring. and iirc, he said they're about £35 brand new.

sorry if this has already been said. i havnt read the whole thread. this might be of interest to u tho.

i had my car mapped about a month ago, i hav'nt replaced the dv yet but the guy at mrc tuning told me if the dv goes.. buy an audi s3 one! apparently they are exactly the same but have a stronger diaphragm and a stronger spring. and iirc, he said they're about £35 brand new.

Well the Audi S3 with BAM engine and the Vrs with AUQ engine share the same DV with the same part number so i can't see it myself. Unless they have just bought out a new one specifically for the BAM engine and ETKA7 doesn't list it.

I already have a forge 007 valve instead of the OEM, and changed the spring within to something stiffer - so far I've exhausted my options.

I will most probably have the map removed, and I'm pretty certain it will be okay - I just find it odd that certain cars dont respond to remaps very well, it doesn't make much sense and wondered if there was a common cause as the symptoms seem to be the same on those affected.

I did read somewhere, someone replaced the sensor on the throttle body? which cured his stuttering/surging? The surging feels like you are physically releasing and depressing the accelerator this is what led me to think it was Turbo/Throttle related. :(

I did read somewhere, someone replaced the sensor on the throttle body?

AIT Sensor

I think if you have tried a new n75 ( i had one that used to surge through the rev range) then its the map. As i have said before there are a few people who have probs with their map for this car surging through the rev range.

I think if you have tried a new n75 ( i had one that used to surge through the rev range) then its the map. As i have said before there are a few people who have probs with their map for this car surging through the rev range.

I've tried the N75J on my car that has the surging, and the surging now is much more noticeable. It was so bad that I went back to the the N75 OEM.