No Boost really confused!!!!!!

[durbans finest]

hows it guys quick question.

i have posted before that i was having a boost problem, car not boosting over 0.4bar. Took the turbo out and the exhuast manifold is cracked in two places replaced the turbo with a brand new k03. checked all the pipes no crackes no leaks. i am really confused now on why the car is not boosting vag com no faults found. The only thing not changed now is the n75valve which i have not changed. Could it be the valve or something else.?

please help some advice will be cost saving.

[walky_talky20]

Could be an N75 issue or a clogged cat or something. You can clamp off (or disconnect and plug) the line to the wastegate actuator. That will make the wastegate stay closed at all times - there will be no boost control at all. As such, you should take it on a very careful test drive and see if you can get your boost gauge to go a little higher. So if you can't get above 6 psi, try to get it to 9 or 10 and then back off. That means the turbo is fully capable of making more boost, but there is some problem with the wastegate control (N75, etc).

[durbans finest]

correct me if i am wrong but if i have to clamp off the line going to the actuator and drive the car the wastegate will stay closed? this means that the line sending the signal so i can say doesnt tell the wastegate to open? a closed wastegate in my knowlage means no boost, a open wastegate means more boost?

[-:vw:-]

When the wastegate opens it bleeds exhaust pressure away from the turbo, this is how boost is controlled by bleeding that pressure and causing the turbo not to spin as fast. If it's closed with no bleed the pressure is not limited and will push all the pressure past the turbo increasing boost to the maximum.

[walky_talky20]

Wastegate is closed by default (held by spring pressure). Regulated boost pressure (from the N75 valve) applies pressure against the diaphragm and pushes the wastegate open.

Closed Wastegate = Lots 'o boost
Open Wastegate = No boost

In actuality, the N75 has to act (engage) in order to prevent boost pressure from reaching the actuator diaphragm. So a lazy or inoperative N75 can limit boost to very low levels. They can also fail is such a way as to give an overboost condition. That failure is more fun.

[durbans finest]

Positive negative situation. More throttle wastegate regulates boost? Remove vac line it stays closed, full boost if I remove the vac line to the wastegate and the car still doesn't boost? Disconnected the n75 and still no boost what does that mean? Didn't remove it from the wastegate just "unplugged it" so to say. May I should load a video for you guys to see?

[durbans finest]

Hi guys i have the video of the car not boosting. Just some specs i am going uphill not so steep 3rd gear and at half throttle. i have also uploaded a photo of my old turbo however the pic is only showing one side but both sides have the crack in it. Also i wanted to know are thise called "stress crackes" if they are then i have bought a new turbo for nothing. Let me know what you guys think.http://www.facebook.com/video/editvi...50257805323530

[Aragorn]

The turbos wastegate opens at 4-5psi.

The N75 valve (when working) hides the boost from the wastegate actuator, allowing the boost to climb past its usual opening pressure. The N75, under the control of the ECU, then lets a controlled amount of pressure thru to open the wastegate once the desired pressure has been reached.

If you electrically disconnect the N75, the valve simply lets all the pressure thru, and so you only get 4-5psi. As a result it sounds like your test has done nothing to prove the turbo is fine.

You need to disconnect the vacuum line to the actuator, so the actuator sees no boost at all, then drive the car EXTREMELY carefully to see if the boost will climb higher than the pressure you're getting just now. Dont go mashing your foot to the floor, just gently apply throttle and see if you get get it to produce more boost. If it does, which is likely, then the problem is either with the N75 valve itself, the wiring to the valve, or there is some other fault which has caused the ECU to decide to limit boost.

Before wasting any more money you need to have a vagcom scan to ensure there are no faults.

[durbans finest]

thanks for the feedback looks like i have alot of work to do tomorrow and wait for the new n75 to arrive. will vag com the car tomorrow to check for any other faults that could cause ecu to limit boost will do the test and let you know the results.

thx again.