N75 or wastegate

[leighaus]

Hey guys, i have a mk4 gti AGU engine...

I've been massively down on boost since having it tuned and its taken some time to try and rectify it.

I had an N75J (ecs race n75) installed, and tried going back to my stock one and neither made much difference, just the n75j got about 2 psi more... so i was hitting either 7 psi or 9 psi with either one, instead of peaking at 21psi and holding 19psi as the race tune was supposed to..

Considering i had not much luck with either n75 i figured my problem lay elsewhere. I've been mucking around in my spare time and i tried disconnecting the N75 top hose that heads to the wastegate and plugging it.

Whilst i get some boost cut and jerking (avoiding WOT, and in 3-4th), im climbing up towards 20psi no problems.


I'm just trying to work out whether this test points to

a) a weak wastegate
b) a dodgy boost line to wastegate
c) a dodgy n75
d) any of the above (or specify other).


I originally thought the n75 was fine as id tried my oem and the ecs a/m variety. Whilst looking around i found some turn of the century audi's go into soft limp with the ecs n75j, so figured it may be the same issue with mine? And as such need a new oem n75?

any help will earn cookies cheers

[h100vw]

Whats the actuator running at. Peak boost with the N75 disconnected electrically.

Gavin

[leighaus]

with all hoses reconnected on the stock n75, it peaks at 5psi when electrically disconnected. I figured this was due to the n75 being disconnected, it would go into limp mode?

I've also taken off the n75 > WG hose and pressure tested it, its fine.

[h100vw]

Without the connector the wastegate opens at the physical setting. 1 PSI at the actuator can make a fair difference under boost. The N75 opens and closes really quick restricting the boost from the manifold reaching the actuator.

Increasing the tension on the actuator would up boost throughout the whole map, as it runs on the duty cycle of the N75. You could increase the disconnected setting to 6PSI, that's what I normally see.

Gavin

[leighaus]

will do mate, cheers. Ill report back any success.

[leighaus]

set wastegate physical setting to 6psi (took a few turns), and on the stock n75 im now getting about a 2.5psi increase to 9.5psi....

Still 10psi missing...

[h100vw]

Sure the turbo isn't broken? Does it drive like 10PSI? or is the gauge gone bad?

[leighaus]

It drives like 10psi. With the actuator / n75 disabled.. It drives like a rocket.

[Bug_racer]

Its not that hard : crimp the wastegate line = gets full boost = N75 the issue
doesnt = turbo/wastegate the issue
/ end thread

[leighaus]

N75 it is then....

Just strange a brand new n75j didn't reach full boost either.. Only 2psi over stock. Anyway.I'll try an OEM one in case the j causes soft limp... Doesn't throw codes however.

[noone]

Re: N75 or wastegate

Have a spare race one in Syd if you want to buy / try. Barely used.

From memory the race is installed what looks like backwards, the length of the barbs should help show orientation. Make sure you're not installing the spare backwards.

[leighaus]

cheers mate, i already have a basically brand new n75 race from ECS... It just doesn't seem like it wants to be friends with my ECU for some reason. So i think ill have to head into a stealership and get an OEM and see if thats helpful.

[Lito]

Have you checked out the wires that connect the N75? If the turbo spools it's nuts off with the Watergate line clamped it has to be something electronic right? Have you tried using a mbc just to see if it'll hold boost?

[leighaus]

wiring appears okay, ill test continuity all the same.

There are no N75s in victorian stealerships atm. Awesome.

Other option is running an MBC, im just kind of uncertain if itll be smooth enough.. As ill need to go buy one, i dont want to be bunnyhopping on and off boost.

[leighaus]

tried flipping my N75J after reading through some real old uk forums... so the long tip was not into the TIP, but towards the WG... which is not how 95% of people install it.. Gained 5psi. boost is a tiny bit jerky in 2nd, first pulls pretty hard.

Still doesnt run to tune spec, or how it feels when bypassing the n75.

Catching up with BFLAT later to try out his n75 and see what happens with that.