GIAC w/N75?

[Sniper512]

I have stg 2+ and I am running the car with a N75 and MBC. If I run the car with just a straight N75 the car will spike to 25psi ahhhh. If I put the car to stock mode it runs perfect and holds about 8-9psi?????? I have a brand new N75 and if I run the car with the MBC in parallel it works great but doesn't seem to pull as hard as when the car worked properly with just the N75. I have checked the plastic T's to and from the N75 and all seems fine. Could the GIAC tuning be at fault??????

[The_Jerbel]

Now that I take a closer look, I realize that the car is running fine in stock mode, which means that the ECU is opening the WG's just fine. The over-boosting problem is not being caused by leaky WG lines or boost reference lines, or a bad N75. It must be a software issue.

[Big Boost]

I installed the MBC yesterday without running it in parallel and it holds 18psi. I capped off the N75, but left it plugged in.

[AK1RA07]

I think I have this problem too.. (GIAC stg 2+ as well) On stock mode, the car runs fine through WOT. Flash to Pump mode and I guess it is overboosting ( still waiting on my boost gauge to arrive ) The car feels like it is slowing down/misfiring/studdering when I try to accelerate. I thought maybe it was because I ran race gas through it and fouled the plugs, but this is still the case after I swapped plugs.

This N75 valve is a mystery to me. Anyone have any links to using an MBC or bypassing it or even where it is I'll search the meantime

[Sniper512]

So not the N75 or its lines:(. Not good at all. I am going to take the lines off today and pressure test them as you said just to be sure.

The car was running great until I switched it to stock mode for the first time going to Calgary to get better fuel economy. After I switched back to pump is when it started messing up and I had to go see "The Jerbel". I ended up getting it back to stock mode again, but it took quite a few times and had to disconnect the battery and then the car ran fine again(stock mode). When I got home again I tried putting it back to pump and the samething happened again 25+psi spikes. Good thing there isn't a single S4 in my town to swap ECU's with lol. I guess I call GIAC?

[The_Jerbel]

I would for sure. You can take off the N75 lines and pressure test them, it won't hurt, but I really don't think that's your problem. Definitely call GIAC and let them know what's going on. I wouldn't be surprised if they've had that conversation before.

[Sniper512]

Maybe they can send me a new tune or update for it or know a fix to this problem.

[Rane_kn]

I think I have this problem too.. The car feels like it is slowing down/misfiring/studdering when I try to accelerate.

Same here (Stage 2 GIAC) acceleration is more like when you row a boat how it gives you jolts of speed rather than a constant climb. and my boost sky rockets just past 20psi then bogs down and up again untill about 6800 I wanna go back to the dyno soon because I had a post on here that graphed just this. and now with the gauge in I can meter it a bit better...but still kong-fuzed

[Sniper512]

Well I went and fiddled with the car and took the MBC out and took the ground off the battery for a bit and then got the car all back together and its fine again. Its really weird. It spikes to 19psi and settles to about 15 sometimes tapers and bit lower but my K03s have probably seen better days.

[o3spec]

mine does the same thing on my stage3, it runs fine on stock and valet but on the pump im running like 30psi then its back and forth back and forth. so i said f it and just run my mbc now, which i don't like because everytime i want to run race gas i have to play with the damn mbc to find the right psi when i could just set it with my laptop when i flashed it!

[Sniper512]

Interesting sounds like this is more common than I thought. I am scared to switch programs now because it may not go back to working its kind of a piss off. I will be going with VAST this time around when I go stage3- very soon.

[kengvang]

has anyone tried running an after market boost controler like apexi or world-racing tbc-1 and by-pass the n75 totally? would a setup like this work for our cars or do we need the n75? these boost controler gives you the abilty to control the turbos any way you want them to act. gear select boost/ rpm boost/ ramping/ low, med, high boost level per throttle.

[Sniper512]

I haven't used one but I am starting to think I may try one. My car is doing the spiking thing again. It is holding like 22psi in the upper gear when rolling into them. The car is great when you launch and bang throught the gear its just when you roll into 3rd or higher that the boost goes too high.

[The_Jerbel]

has anyone tried running an after market boost controler like apexi or world-racing tbc-1 and by-pass the n75 totally? would a setup like this work for our cars or do we need the n75? these boost controler gives you the abilty to control the turbos any way you want them to act. gear select boost/ rpm boost/ ramping/ low, med, high boost level per throttle.

It's very hard to make these boost controllers work properly with our ECU's.
It's quite easy to install an MBC in standalone and just set the peak pressure and leave it at that. Why play with the complicated EBC crap when the MBC works just fine?

[The_Jerbel]

I haven't used one but I am starting to think I may try one. My car is doing the spiking thing again. It is holding like 22psi in the upper gear when rolling into them. The car is great when you launch and bang throught the gear its just when you roll into 3rd or higher that the boost goes too high.

What pressure are you at at redline?

[Sniper512]

At 5000 it was still at 22psi so I let off I got pics its kind of scary lol. When I launch the car and rip through the gear for a 1/4 mile run the car hits like 19psi and settles to 15psi by redline its only when I roll in to the throttle that it spikes and generally holds the boost.

If I run a MCB in standalone I have horrible part throttle eg. the boost will shoot to 10psi or 15psi almost instantly at part throttle then drop to 5 psi really fast causing a jerking feel. Is this still FC at part throttle even though I have a TCD? I would stick with the MBC if this part throttle was not an issue.

PS The inlets are silver;)

[Sniper512]

Okay so I am retarded. I left my TCD in with just the N75 i wasn't thinking. So I did some new logs because the car is now hitting TC yay.
Block# 115

0.40,2720,25.6,890.0,900
1.22,2680,26.3,890.0,900
2.11,2680,36.1,890.0,900
2.91,2760,97.0,1810.0,1120
3.71,2960,154.9,1950.0,1750.0
4.62,3240,160.9,1950.0,2160.0
5.53,3520,175.9,1920.0,2430.0
6.43,3800,172.9,1910.0,2050.0
7.25,4000,162.4,2000.0,1880.0
8.17,4280,174.4,1970.0,2090.0
8.99,4520,157.1,1940.0,1920.0
9.85,4480,78.2,890.0,2070.0
10.72,4560,9.0,890.0,990.0

Block#119
0.00,2720,0.0,0.0,900.0
0.80,2680,0.0,0.0,900.0
1.71,2680,0.0,0.0,900.0
2.51,2720,0.0,45.1,940.0
3.31,2840,0.6,95.3,1410.0
4.13,3080,0.6,88.2,2140.0
5.04,3360,0.0,93.7,1810.0
5.93,3640,0.0,68.6,1960.0
6.85,3920,0.0,73.7,2240.0
7.76,4160,-0.3,84.7,2170.0
8.57,4400,-4.5,78.0,1970.0
9.42,4640,-4.8,79.2,1920.0
10.29,4640,-4.8,0.0,1110.0

So I am hitting about 22psi and hitting TC Whats with the duty cycle? I don't understand it.

[The_Jerbel]

Do you think you could graph that in Microsoft excel and then post the graph? Or just email me the excel file with the info and I can graph it.

[Sniper512]

Sure that would be awesome I'll send it right now. I put the MBC back in Parallel and all is well got the boost set to 18psi no fuel cut or anything, but I would still like to figure out what is going on with this before I go to Stg3- in the next month.

[milehighpilot]

have you guys settled this issue?

i just started doing this yesterday however i have apr chip... as like you said its only from a roll and above 3rd do i get this... but mine spikes 25 then drops in steps to 20 and you can feel the car adjust and loses power then drops to 15 and i have all the power back that i had at 25...

[Sniper512]

Still having the problem. I have to run a MBC to keep the spiking down. I found a hole in my F-Hose and fixed that but it is still spiking way to high. I may get the Vast stg2 tune and see if it goes away its all I can think of now is that it is the tune. COuld be another boost leak somewhere like the intercoolers or something like that. I have a front mount to put on and if that doesn't fix it I am getting a new tune. Also I am gonna try replacing the spider hose.

[updaboost]

Interesting thread... when i installed my vast fueling i broke 2 n75s. Prince at VAST couldnt figure out why.. so now i run the MBC standalone at 22 psi and car runs great... what's up with these n75 wastegates...? Prince told me the mbc set-up works fine just be aware of boost creep at changing altitudes and outdoor temps. This is prevented if n75 works properly..my dyno number in my sig are with the mbc set-up

[Sniper512]

Ya I think I may go back to the MBC and see how it is. When I tried MBC only before I had horrible part throttle to the point where the car felt gutless unless I was at WOT. I am hoping this was from the hole I found in my F-hose. Could this has been the problem of my part throttle with a MBC? or is it normal to feel that way with one?

[The_Jerbel]

I can almost guarantee that your issue was from having that massive boost leak...