n75 valve on a 1z engine help?

right i have a 1z engine and have just fitted a boost gauge to it to find that the boost is spiking at 1.5bar then drops to 0.8 and then about 1.2 and carries on surging, have looked around and have found its the n75 valve. So what should i do? is their one i can get that allows more boost? or what should i go about next??

delete it?

just simply remove it all together and place a mechanical boost controller in??

Did the car have any driveability problems prior to your gauge install? The ECU controls the boost, via the N75. If it runs properly, there are no DTCs, chances are it is all normal. Although it really should not vary all that much, so you may have an N75 issue or a leaky/clogged hose somewhere, weak/binding wastegate return spring/linkage, etc.

just put a mechanical controller linked up as suggested so its sort of in series with the n75 valve and the spike has gone now so looks like a faulty n75 valve i did notice when i was instaliing it oily residue in the lines so was probably this, only issue now is how is the boost adjusted?? on the wastegate arm?

<Bull$hit deleted>

Worst advice you could have given!

NEVER delete an N75!

YOU WILL overspeed the turbo and risk destroying the turbo AND engine!

Would you do this on an ALH with a VNT? This engine is no different!

For you newbies you had better learn how these engines are controlled before spouting off Bull$hit like that!

so what iv done is right run it in tandem with the n75 valve? as it has stopped the spikes, how is the boost pressure increased now?? on the wastegate?

As long as you have a functioning N75 and use a bleed to LIMIT the spikes, you are good to go. DO NOT over-ride the control of the N75, assist it but allow it (the bleed) to regulate maximum boost pressure by tricking the systems control.

The 1Z (Garrett) turbo is pretty weak to begin with, it has the lowest TIT threshold being 1550F max sustained temperature. The KKK (AHU) and VNT(ALH) Garrett are all in the 1650F range meaing a better allow and more margin for performance mods.

Also I have seen in person melted turbines on the 1Z Garretts due to retarded timing, make sure you are running above the mid range and ideally at the top of the range to minimize TIT's.

so to adjust the boost pressure is it on the wastegate? and which way do i turn it?

You adjust pressure via the ECU not the turbo.

It's controlled by the ECU and not some dumb mechancal system like older cars.

well that is good to know i am doing it all wrong concidering all the reading I did 6+ years ago on installing and using one.

Drivbiwire said:

You adjust pressure via the ECU not the turbo.

It's controlled by the ECU and not some dumb mechancal system like older cars.

Click to expand...

Sorry for reviving an old thread but I wanna be sure I understood this.
So the intake pressure goes to the N75 which, depending on the ECU mapping, will or will not direct it to the wastegate to open it and prevent overboost. Right?

So to increase the pressure you could either remap the ECU or shorten the rod of the wastegate ?

This is correct - the wastegate in these cars works on manifold pressure (boost).

Adjusting the rod is just fishing for limp mode when the ECU detects it was not able to limit boost per the boost map.

Best to get a tuned ECU - you will need to determine which ECU you have and contact a tuner which can supply the chips with a modified map. Also make sure your ECU is socketed to accept the chips, or learn how to solder either the chips or sockets.

One more curiosity. Would shortening the rod by a small amount (let's say you would up the boost from 1 bar to 1.1) make the car go into limp mode? And most importantly, will the boost be higher just at a specific RPM or would it be equally raised across the whole RPM range? I hope I explained it clear enough

See, it doesn`t work that way.

-Car makes boost.
-Boost reaches limit (12-14 psi or just under 1 bar on a stock tune for a 1Z)
-ECU commands an increase in the N75 duty cycle to direct positive manifold pressure to the wastegate actuator.
-ECU looks for manifold pressure to cap at 12-14 PSI depending on throttle and load, and adjusts N75 accordingly

If you adjust the wastegate rod so that WG is harder to open, and the N75 needs to command a higher duty cycle, the ECU will ramp up the N75 duty cycle to compensate.

It will do so until it reaches a limit of how far and how long it compensates, and if it exceeds that, it will then put the car into limp mode.

Your car will either reach the adjustment and maintain 12-14psi boost, or it will exceed the limits set in the ECU and go into limp mode.

If it`s extra power (cheap) you are after, go after fuel - look up EVRY mod and do that instead.

I did a cheap IQ adjustment using hammer mod. The car feels marginally quicker but i'm pleased since it doesn't smoke. I'm thinking of upgrading the injectors but I would've liked to "add some air" to all this. And since I don't have plans to mount a FMIC or anything like that I needed to keep it simple. Maybe i'll go for a remap although the best tuner (probably) in my region refused to do a remap on a friend's 1z since "it's too much of a hassle and the results are not spectacular". Dissapointing response for someone like him but, oh well...

Thanks for the explanation !

I was quite happy with an 18 psi tune and pp520 nozzles on my 1Z. Not "spectacular" per se, but made the car much better. Mine was a Passat, so the above would make your mk3 even faster.

Reviving this old thread. It's an audi 80 b4 with the "old gen" ECU, MSA6 i believe. The maf is actually a vaf (bosch). So, i fitted a boost gauge and AFN injectors. Found out my n75 was badly connected. The car was slowly building boost up to 1.5 bar ! It's been driving like this for over 8 years, never had it in limp mode.
Connected properly, it responds quicker and peaks at 0.9bar, but drops slowly to 0.7-0.6 in high revs in high gears (5th gear-close to 4000rpm). This drop doesn't happen in gears 1, 2, 3. Even with this pressure difference i took it for 2 runs on an uphill, i would say it drives better with 0.9bar because of the faster spool up.
I adjusted the wg rod so that the peak boost is now 1.1 bar but it's quickly corrected to 0.9bar.
Now the question/problem : Considering the extra fueling, how could i make it keep a constant boost of 1-1.1 bar? Would a boost controller work? But where should it be fitted? Between the n75 and wastegate? Or between the intake and MAP (in this car, the MAP sits behind the airfilter, connected to the IC via a long hose).
Note : the ecu is 55 pin, with eprom. The only way to reflash it i heard is by having it under a UV lamp etc. Haven't found anyone to map it; there is one guy but he swears there is no way to adjust the boost values.

Sorry for the long post