just fitted my boost gauge ( ill post pics up later ) , what pressure does it run at ? its a standard MK1 VRS

should be about 7psi on a standard car buddy get it mapped and should be 1 bar:thumbup:

which is about 0.3-0.4 bar ? here is the picture of it . i wanna re-map it but i need to sort the under boosting problem first

yep about that what do you mean by underboosting problem buddy expain???

ive got the code 17705 :thumbdwn: i didnt think you can re-map it with this .

Mine runs at about 10 psi with a front mounted intercooler, as far as i know it is not remapped, how much boost does a remapped octy run???

Edit: i see, around 14 psi then for a remapped motor, wonder why mine is way above the 7 psi then?

Because you're right an Clive is wrong :P:P:D

Standard is 9-10 psi

oooooooppppppppsssssss i was close lol

cant be clever all the time lol :P

Mine (k04) runs 20-23 psi.

ive got the code 17705 :thumbdwn: i didnt think you can re-map it with this .

did you try a new n75??

i could mean you need to put a new throttle body on....i have my old one for sale and i didnt have this problem so as good as new can do you a good price as you really dont want to pay £200+

can do it on a semi sale and return if you want pm me

Mine (k04) runs 20-23 psi.

thats because its a bigger turbo so will what does it hold throught he rev range ( in bar please):confused:

Clive..............Wrong :eek:

Clive..............Wrong :eek:

you cheeky git :P:P

(note to self no christmas card for welshloon:D)

how much boost does a remapped octy run???

I have a CC phase1+ remap & according to my boost gauge the peak boost Is 21psi (1.45bar) before falling back & thats with a fmic on a standard K03s turbo:rotz:

Mine boosts up to 21psi on a standard turbo with Custom Code remap :eek:

To check your peak boost pressure you must accelerate the vehicle in 3rd gear at full throttle from 2000rpm, and take your reading at 2800rpm. The specified value should be between 0.16 and 0.17MPa. That's what Skoda say.....

So an absolute pressure of 23.2psi to 24.7psi, and gauge pressure of 8.5psi to 10psi.

Mine runs 10psi when standard, 17psi with an APR stage 1 map and 5psi in limp.

Mine ran 9.8 and 10.1 on a rolling road but for some reason the Liquid gauge thinks it's running as much as 11.1 psi

FWIW 7psi is the standard boost pressure on the 150bhp 1.8T Octavias.

ive put a new DV valve , pressure hose and air intake temp sensor . the air intake temp sensor was sorted out my revs on cold because it use to go up and down between 1000rpm and 400rpm and the stall itself .

i notice it pulled better when i put a new DV on compared to the forge007p .

skoda recommend if the fault reoccurs it will require a new throttle body and system clean so thats the next thing i will be changing .

standard mines running about 0.3-0.5 bar then half way home she wanted to be a bitch and wouldnt go over 0.2 bar :thumbdwn:

standard mines running about 0.3-0.5 bar then half way home she wanted to be a bitch and wouldnt go over 0.2 bar :thumbdwn:

Ouch, yeah definately not boosting like it should be - should be just over 0.7 bar standard. The 17705 fault can be a leak in one of several pressure hoses, I think the most popular ones are the Y-shaped pipe ones on the battery side of the engine, or one of the ones under the inlet manifold close to the oil dipstick. So maybe worth checking those for leaks too before replacing the throttle?

pipes have been checked . had the engine running to and checked the pipes and the revs stayed the same . its been running at half a bar past 2 days

Doesn't 0.3-0.5 bar sound like a faulty n75? I thought 0.3 is the turbo's "self-limit" and without n75 it will not boost more. About two months ago my n75-to-actuator vacuum host popped off and it wouldn't boost more than 0.3.

@westallc: it holds 1.3-1.4bar as far as i remember.

Doesn't 0.3-0.5 bar sound like a faulty n75? I thought 0.3 is the turbo's "self-limit" and without n75 it will not boost more. About two months ago my n75-to-actuator vacuum host popped off and it wouldn't boost more than 0.3.

@westallc: it holds 1.3-1.4bar as far as i remember.

That hose from the N75 to the wastegate actuator is actually a pressure hose, not a vacuum one like the one on the DV.

It is the actuator spring that holds the wastegate closed, and the manifold pressure (P3) that blows it open. The pressure hose that runs to the actuator acts on a diaphragm that sits on the spring and rod assembly, which essentially reduces the pre-load on the wastegate valve and allows P3 to overcome the spring, opening the wastegate valve.

So if you pulled off the hose to the actuator, it wouldn't normally boost less, but more (no idea how stiff the spring is and what it's limit is). I'm guessing the N75 recognised that it was blowing to atmosphere, which in turn told the ECU to activate the N249 and suck open the DV to drop off the boost. The only other way I can think off would be to reduce the fuel and drop down P3, which in turn would drop your boost pressure (P2).

Sorry for the rant there! Wastegates, pneumatic actuators and control valves are my job now, so it's all I ever think about!

Hmm, i don't exactly understand the "which essentially reduces the pre-load on the wastegate valve and allows P3 to overcome the spring, opening the wastegate valve" part. I mean, as far as I know the N75's job is to actually command the wastegate to close, so the exhaust gasses can go inside the turbo and not out the wastegate and into the exhaust. Also, afaik, the spring for the wastegate is preset at 0.3bar and in absence of the N75's command the wastegate would always open at 0.3bar and the turbo would not produce any higher pressure. That's why I thought that since my hose was off, the N75 could not command the wastegate to close, hence no boost, the wastegate was opening at 0.3bar (spring preset) and all the boost was going out the exhaust.

And actually this is what the car felt like: up to about 2000rpm it would pull, I would hear the turbo spool up but then nothing, just a huge dump valve noise (but continuous hissing, not just one big hiss sound), which I guess was all the pressure escaping out the wastegate.

Do I have this all wrong?...

note: I had no codes after the whole deal. I drove like 2km, stopped, put the hose back in and checked, no codes were stored.

note2: you are right, it's a pressure hose, but as a non-english speaker I just call them all vacuum hoses (since I actually replaced most of them with silicone vacuum hoses from forge )

ps: sorry for the continued rant

Edited 5 August, 200916 yr by jmf

That's OK mate, it's a common point of confusion. Most people at work think about it the wrong way around! Your English is pretty perfect by the way, better than a lot of English people anyway!

Here is my official definition of a wastegate actuator:

"The function of the actuator is to hold the wastegate valve closed against the exhaust gas pressure until the required boost pressure is achieved and then to control the opening of the valve by balancing the air pressure in the capsule against the spring force and turbine inlet pressure acting on the wastegate valve."

So it is the spring that holds the wastegate valve closed. It is the exhaust manifold pressure that opens the wastegate valve. The pressure supplied to the actuator 'weakens' the spring, allowing the exhaust manifold pressure to blow the valve open.

So with no pressure feed to the actuator, and nothing to 'weaken' the spring, the wastegate valve wouldn't open until some massive (probably not even achievable) exhaust manifold pressure was reached. Basically your be running without a wastegate.

Luckily the command valve (N75) notices the incorrect pressure change, and the ECU reduces fuel to reduce P3 and keep turbo speeds down (limp mode like you experienced). The constant hiss when you hit 2000rpm will have been the N249 opening the DV, by connecting it to the vacuum reservoir rather than the inlet manifold (another protection mode).

So all these people that have bypassed their N249 and N75 valves are living life dangerously!

Well, this is certainly new to me. I mean, everywhere I read it was written that without the n75 to close the wastegate the turbo would regulate itself to no more than some very low pressure, like wikipedia "The primary function of the wastegate is to regulate the maximum boost pressure in turbocharger systems, to protect the engine and the turbocharger". Also another source of n75 "knowledge": Wastegate bypass regulator valve - S4Wiki .

Also, from your definition I don't clearly see how my thinking is wrong: "The function of the actuator is to hold the wastegate valve closed against the exhaust gas pressure UNTIL the required boost pressure is achieved...". Which, to me, means that if you floor it the actuator will close the wastegate to ensure that requested boost is reached, and only AFTER that will allow the wastegate to open in a controlled fashion so requested boost is sustained for as long as needed.

Although I can see how one can think about it from the other direction: the wastegate is always closed and the n75 opens it to prevent overboost. So basically the n75's job is not to help the turbo produce boost (by forcing air into the turbo), but to help the turbo NOT overboost (because it would produce the needed boost anyway). This seems weird to me, but thanks for the explanations...

Ah, another point: if what you're saying is true, how come a lot of people seem to have boost problems because of faulty n75s. Boost problems = low boost. I mean, if the turbo would produce enough boost (because the wastegate would never open since the n75 is fauly) they would have to have overboost problems, not low boost problems, right?