Boost n75

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Joe9090

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Right, iv got an issue with boost for some reason,
Sometimes it bòosts normal and sometimes it boosts high. I dont have a boost guage but i can notice it pulls very quickly,
I had this problem when i brought this car,
It gave me a fault code 17956
I was told it could be the n75.
I replaced the n75 valve .
And noticed its still doing it.
So i pulled back the rubber and check wiring and one wire was short,
So i rewired it and all was ok. Boost was back to normal.
Now i noticed its still doing it again today. Checked wiring etc and all is ok. Why is it still boosting high and low again.
But runs fine when normal.
Can anyone look up fault code 17956.
It was scanned via vag com software if thats anygood?
fault code was deleted and hasnt come since but car behaves like this.
 
17956 means theres a break in the wiring to the N75 valve, or the valve itself is bust. Since you've replaced the valve, its probably the wiring.

A faulty N75 usually gives you low boost. Unplug the N75 and go for a drive and see what happens.

I had this on my first A4, ended up replacing about a foot of wiring to the N75 valve, must've had a break in it somewhere.

Its worth making sure the N75 is installed the correct way round.
 
As i said one wire was short and has been rewired and was running fine but il check if its fitted right way round. The fault code did not reappear after i rewired it. And was running fine, But the car is running in a similar fashion after 2-3 days of driving.
 
audi upgrades
well unplug it and see what happens, it should give you low boost all the time. If its still acting up, then theres something else going on. If its just low boost then you need to take a closer look at the wiring etc again.

With mine, there was no visible breaks in the cable. It all looked fine, but must've broken inside.
 
Im going to unplug and recheck. But iv just installed the boost guage and getting only 5psi? My audi is the 150 sport version?
 
Because iv changed the n75 when i first diagnosed it, could it be down to a maf sensor being.
I remeber the vag scan saying something about a faulty maf and gave a code. Can this put the boost lower? Or under power the engine?
 
yes, if there are any other fault codes it can put the car into limp mode which gives you limited boost.
 
Right understood. Mechanic deleted that fault code saying it should be ok. Another problem im getting since the boost guage install is that instead of getting boost out of the manifold im getting suction?
And now the boost guage aint working as it should. Iv upload a pic with this. Can someone have a look and point me in the right direction. Getting fed up now.
 

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I tapped my boost gauge into the Fuel pressure regulator, I used a T piece going from that to the Inlet manifold, and at the bottom of your pic that blue silicone tube goes to the top of my DV valve

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I'll get you some pictures in about half hour mate

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That clear piping looks twisted badly.

And id run it from the FPR aswell as looks neater and through the servo pipe grommet and down through the ecu box.
 
You need to figure out whats going on rather than trying to bodge things up with MBC's and whatnot.

Fit the N75, leave it unplugged, and drive the car. If it then consistently has 5psi, you need to get the N75 connected and working.

If its still acting up with the N75 unplugged, then theres some other issue such as a boost leak or a bad MAF or similar.

Also, stick to one thread, its annoying having two threads going for the same issue.
 
that clear pipe has likely sucked flat and or kinked. I always use the port on the servo pipe, pull the little green cap and stuff the pipe for the gauge on there.
 
Sorry dude to run 2 threads. Anyway in regards to the pipe, the pipe has been replaced as old one was short and over streching, new ones working a treat so far.
Cars been running fine and boosting well. To 10 psi. A new Maf has arrived and will be fitted tomorrow. Next 2 steps are to change the O2 sensor and remap. N75 i will reconect and give update. Mean while im turning boost down to 6 -7psi on mbc, until i get my car booked in. Any advice on which remap is best. Thanks
 
If you have a TQS then it's most probably a ecu and chip job with regard to remapping

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1.8T Sport not quattro. Can that be remapped?
 
I have a AJL 180hp ECU for sale if your interested will just need immo deleting or recoded to your car. Drop us a PM if your interested.
 
ODB-ish. It needs 12v applied to a certain pin, but i'm sure you can patch that in in such a way that you can apply that 12v with it in the car.
 
Right, took it to Manchester and back and drove fine on the way going, but at times it felt like there was no boost at all. Felt sluggish etc. Then at times it felt quick. Spoke to a friend and he reckons i got a sticky vanes turbo problem
Can anyone point to me what i can do.
Iv spent £££s on it and still no cure.
Im on the verge to selling it.
 
When its boosting fine it wiĺl boost to 7-8 psi and it feels very strong but drop to 5-6 psi , but then its boosting sometimes around 6psi to 5psi amount its like it dragging the car and feels very flat no matter much i force it.
Can the actuator / wastegate be causing this?
Iv changed most vaccum pipes with silicone piping as old pipes were very poor condition considering the car has 161k on clocks.
 
Last edited:
Feels very quick on lower gears sometimes and seems to struggle after 75mph. Its like iv got to really force it to move. And sometimes by driving it hard it starts boosting again.
 
I've said this before, and i'm not sure if you've done it but unplug the N75 (leave all its hoses as per factory, just remove the electrical connection), and drive the car around for a few days.

If you do that, you should get a flat 5psi of boost and you can see if the car acts the same.

If, with the N75 disconnected, you get a nice stable amount of power, that isnt changing, you can put the N75 back on and compare.

If its dropping to 5psi with the n75 connected, then either the ECU is going into limp mode because its unhappy with something (there should be a fault code for this) or theres a break in the wiring to the N75 valve which is causing it to become disconnected at random.
 
aragorn said:
I've said this before, and i'm not sure if you've done it but unplug the N75 (leave all its hoses as per factory, just remove the electrical connection), and drive the car around for a few days.

If you do that, you should get a flat 5psi of boost and you can see if the car acts the same.

If, with the N75 disconnected, you get a nice stable amount of power, that isnt changing, you can put the N75 back on and compare.

If its dropping to 5psi with the n75 connected, then either the ECU is going into limp mode because its unhappy with something (there should be a fault code for this) or theres a break in the wiring to the N75 valve which is causing it to become disconnected at random.
Click to expand...


Right iv done what you said, its boosting fine, but it started juddering on startup and slight missfire so i scanned for fault codes and the only one coming up is 16514
What is this indicating to. Thanks
 
Right are these a dealer part only? And is this the one connected to exhaust at front under bonnet.
 
No you can get them from many places. I'd suggest you stick to a genuine bosch part.

And yes, its in the exhaust just behind the turbo.
 
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