LEON CR fluttering boost problem

[beezasport]

i have no noise either and it runs better in the hot weather. I've tried a few different DV's and also i have chanced the TIP for a samco one. Like scotty b said i think its a valve somewhere along the line.
my car was standard when i picked it up and it did this so i changed the MAF, no difference. uprated DV and TIP still the same and its not been remapped yet.
Its been into SEAT but it wont do it when i'm there its only intermitant.

 

[sargey]

COR. 2 pages ive had to read since i last posted

mine is a stock map, stock engine apart from induction kit and Split-R DV.

The only sound I get is a premature dump when the boost fluctuates around 2000-2500 rpm, using low throttle, in 1st and second. It goes up to around 0PSI then drops to about -10 InHg and then back up again

Full load no problems. boost holds nicely around 9Psi, sometimes peaks at 10 but drops to 9.

Ive had a new MAF and new N249, im going to book the car in for a pressure test to check for any leakage. If that comes back negative which it should then SOD KNOWS

 

[Scotty_b]

So we can speculate that its a stock part at fault if some of you are getting the issue with no or next to no mods. Ive noticed as well mine does it far worse after ive given the car a bit of a rip then try to cruise at a higher speed with minimal boost. My car is going into VAG Tech on Saturday with the instructions it doesn’t come out until its fixed! Its amazing how such a small thing can get on your tits!

 

[sargey]

Wheres VAG tech? Not coming out til its fixed....lol. what if they never find the problem? lol
It doesnt "always" hack me off, only sometimes, i try to ignore it as the car runs fine APART FROM THIS (touching wood)

 

[Scotty_b]

Its MK way. In that case they have a veeeeery nice 450bhp r32 in there!
Its anoying in that i cant find the issue and it could be something expensive/not doing the car any good

 

[sargey]

Did not look at it that way, you have a point! you will get back to us on your findings wont you?

450bhp R32? is that the big turbo'd one like the one grants trying to do at Westec?

 

[Scotty_b]

Yeah ive said theres no rush to get it back so maybe a week or so but as soon as its out i will post up the findings as they can do far more than i (getting new parts and fully testing things)

No its the HPA 450 kit, they do a 600bhp version!

 

[sargey]

thats just crazy, why cant cars be simple eh? spending money on it is starting to do my head in, as soon as one thing is sorted something else goes wrong!

 

[davymcgiver]

what is a N75 valve and diverter valve?

 

[richybigman]

Diverter valve is what you may know as a dump valve but it recirculates instead of making the blow off noise. The N75 valve is the boost controller valve i think.

 

[Scotty_b]

N75 is an electronic bleed valve. It fools the actuator into thinking the cars running less power than it is

 

[richybigman]

N75 is an electronic bleed valve. It fools the actuator into thinking the cars running less power than it is

I was wrong. What's the valve called that controlls the boost? I bet i'm gonna look stupid as it's probably called the boost control valve! LOL!

 

[Feel]

Hmmm, not sure about that description Scotty...

Also, people seem to be reporting different issues - sportbilly has reported full throttle surging as did the OP and Pabs, but some of you are mentioning part throttle surging. I'm wondering if these are the same issues.

Brendy re-posted an old post about how the N75 works, and how to adjust it to smooth out the boost, but I remember doing that was seen as a last resort/big no no as it reduces the boost.

There's some reference to Boost Surge on the vwvortex, including this:

http://media.putfile.com/oscillation

Look familiar?

 

[Feel]

I was wrong. What's the valve called that controlls the boost? I bet i'm gonna look stupid as it's probably called the boost control valve! LOL!

Nope, I would say you're right.

 

[Feel]

 

[Scotty_b]

Feel where do you get these pics from! There great!

Well the N75 is an electrical bleed valve, maybe I didn’t explain it right.
Now we know that the actuator is set to release the turbo pressure when the spring pressure is overcome. In some of the original turbo’d cars this was how boost was controlled and you could set the boost by adjusting the actuator to be stronger or weaker depending. A bleed valve does what it says on the tin, the feed that would have gone straight to the wastegate actuator goes into the bleed valve and is then sent back into the actuator. To make the valve work air is “bleed” off so that the actuator only sees a percentage of the total pressure therefore running the pressure higher and for longer. Now to set this you used to turn a dial on the top to set the amount that’s bleed off.
The N75 works in the exact same way feeding the “bleed” back into the TIP and rather than turning a mechanical valve the ECU controls how much air is diverted away from the actuator

 

[sargey]

VAG-COM says the N249 is the boost control valve but SEAT call it the solonoid changeover valve

 

[Scotty_b]

Looking at that pic im wondering if the MAP sensors are playing up as they tend to get over looked and i know my turbo can spike out of there range

 

[speedsix]

I think it's simply a case of the N75 struggling to control so much boost. Aside from fitting an electronic boost controller I can't see it being completely irradiated. Like I say I improved it greatly by swapping my N75F for the older superseded N75C.

 

[richybigman]

I've got a Greddy spec 2 boost controller i'm gonna try at some point to see if i can get it to hold constant boost but i was told by a garage that boost contollers hold boost but don't tail off at the end which causes compressor stall which will in the end kill the turbo. But i'm gonna give it a try anyway!