Hi!
New guy here

I've got a VERY annoying problem.

My story starts with my car, chiptuned in Sweden (i'm Swedish so that makes kinda sense :P) boost pressure @ 1.35 bar (approx 19.5 psi)

One day my boost pressure started to pulse up and down (+/-0.1 bar) and then stabilize itself. On another occasion, the boost just went up top 1.25 bar but no pulses.
I solved this problem by replacing the n75 with a new one.
The car was chiptuned approx 5-6 months before the problem showed.

So, recently, the car was acting the exact same way again, this is 2 weeks after Ireplaced the n75.
A day after that, the boost started toskyrocket and the fuel-cut gets in.

I thought it was the n75 was the culprit even this time, I tested the wastegate, the hoses are good and limp-mode (or what to call it :P) works fine, i pulled the wire to the n75 and it works, but boost is @ 0.35 bar:P

I changed back to my old n75 to test some more, and it worked, but only for a minute or 2 and then the boost skyrockets again.

So I'm wondering, what causes the n75's to break?
The car is a A4 1.8t.

Please help!

 

have you changed your dv? it is probably that and not the n75

 

dv wouldn't cause it to overboost. only the n75/wg causes that. don't know whats up with your problem tho. replacing the n75 should have fixed the problem. my only guess is that your tuning doesn't like your n75. some tuning doesn't like certain n75's and you get weird problems.

you can either play around with different valves (costly) or just get a mbc so you dont have to deal with the n75. i would suggest the mbc

 

Well, the strange part is, that everything was fine for approx 5-6 months, and now all of a sudden, it busts n75's all the time...

What is a "dv" and a "mbc"?

It couldn't be the cable to the n75 that's wearing down?

 

diverter valve and manual boost controller


i was just thinking dv, cause of the way his boost fluctuates, and cust in and out

i would have thought, if it was a torn diaphragm that it might allow too much boost


what i would do is talk to the people that did your tunning

 

dv is diverter valve, you need to upgrade it to handle the extra boost. you can get a 710n for cheap, or an aftermarket one like forge, baileys, evo, etc... I'd suggest the forge 007 or 006 (pretty much the same thing)

mbc is manual boost controller. it will replace your n75 and control your wg. so you dont have to use a n75, you just leave it plugged in electronically and tie it off to the side

 

Diverter valve = Blow off valve? I have a new one, a piston from a swedish tuner-company.
I talked to the tuners, but all they want to do is to troubleshoot it, and that costs, of course.

I don't want an MBC, because if you press the pedal at low revs, the turbo will charge too much for that rev and the pressure will me stronger (of course :P) and that will damage the pistons. My program limits the boost at lower revs until higher revs, just to spare the pistons.


I noticed something today, though.
With full throttleon 2nd gear, the boost acted as it should, but on 3rd and higher, it actedstrange again. Even after trying with the 2nd gear again, it still acted strange. So something is...strange :P

 

yeah diverter valve is a blow off valve that recirculates.

and you dont have anything to worry about with the pistons. they are Mahle Forged pistons that have seen excess of 700hp. they are extremely strong.

 

Oh, OK, but what about the crankshafts?

Anyhow, no one who has a clue about the n75? :P
I reeeeeally want to use that feature, so to speak.

 

i dont think anyone has broken a crank yet. and there are 900+ hp 1.8t's out there. the weakest point of the internals is the rods. they can handle around 330ish tq depending on how good the tune is. the pistons have seen 700hp, the stock head can rev to 7.5k. these engines are very strong

dont know whats up with the n75 tho. i've caused mine to overboost when i installed it wrong, but thats not the case with you since it worked for a while then stops. what happens when you swap it again?