B5 A4 Overboost

**SimonA4TQ** · 07-04-2008 09:56 AM

My 96 1.8T is over boosting when the turbo first spools under full throtle. This is not just a spike, It will go well over 25psi. IT occurs most of the time with the preformance chip in and sporaticly with the standard chip. If the accelerator is eased on to full throtle it never hapens, and it rarely hapens above 3000rpm.
I have tried a new ECU, MAF, MAP, N75 & intake temp sensor with on results.
I have also tried a manual boost controler which works but runs lean.
Has anyone heard of this problem or got any ideas?

Any imput would be greatly apreciated.

**UCFQuattroguy** · 07-04-2008 12:40 PM

Try running the MBC in-line with the N75. That's how mine is setup and I've got a rock solid boost profile. All you'll need to do is have a laptop (Vag-Com) with you for a little bit to get the peak boost to match whatever the ECU requests, the N75 will do the rest of the work for you.

**oneighty** · 07-06-2008 12:06 PM

Simon, are you in Melbourne, Fl? I lve right down in Sebastian not too far away, Ive been trying to iron out this problem as well and UCF's method with VAGCOM is about as close as Ive come to smoothing it out. Although I think he means to have the MBC in parallel, not in line. I have VAGCOM if you need some help.

**mike-2ptzero** · 07-06-2008 01:26 PM

Originally Posted by oneighty

Simon, are you in Melbourne, Fl? I lve right down in Sebastian not too far away, Ive been trying to iron out this problem as well and UCF's method with VAGCOM is about as close as Ive come to smoothing it out. Although I think he means to have the MBC in parallel, not in line. I have VAGCOM if you need some help.

He most likely lives in Australia seeing that he owns a 96 1.8T and the 1.8T was not sold till 97 here.

**SimonA4TQ** · 07-07-2008 05:15 AM

Yup Melbourne Australia.
Thanks for your sugestions guys.
I have not tried the MBC in line or in paralel with N75 as both of these scenarios will still allow the MBC to bleed off all boost untill the MBC set point regardles of what the N75 is dooing. which would still let the car run lean on light throtle with high boost.
Does your MBC bleed the boost of to atmosphere as mine does, or does it just keep the line blocked untill set point? if so what type is it?

**oneighty** · 07-07-2008 06:13 AM

I just run a regular ball and spring MBC with a bleed hole which is supposed to prevent the wastegate from getting stuck closed. I run it in parallel because I dont want to raise the boost, just limit that initial surge. You still have to log to get it adjusted close to the requested boost level via block 115(if I remember correctly).

**mike-2ptzero** · 07-07-2008 07:42 AM

Originally Posted by SimonA4TQ

Yup Melbourne Australia.
Thanks for your sugestions guys.
I have not tried the MBC in line or in paralel with N75 as both of these scenarios will still allow the MBC to bleed off all boost untill the MBC set point regardles of what the N75 is dooing. which would still let the car run lean on light throtle with high boost.
Does your MBC bleed the boost of to atmosphere as mine does, or does it just keep the line blocked untill set point? if so what type is it?

The bleed off type only bleed off once your making more boost then what it is set at and doesn't bleed till that point so it should not cause you to run lean at part throttle. They also make bleed off mbc's that have a 3rd nipple which allows you to return that air back to the TIP just like the N75 valve. The ones that block are better since they dont release the pressure to the wg till it has hit its set psi.

**SimonA4TQ** · 07-08-2008 03:40 AM

ok I will get some plumbing and give it a try in paralell.
So I take it that if the MBC is set to 15psi and I try to blow through it, I wont be able to.
I will keep you informed.