Evening all, well it is in Scotland anyway.

Ok so i'm new to this forum and i have spent the last few days having a wee look about and feel i should join and help out with anything i can too.

But first (Sorry) i have a question.

I am running a Stock A4 1.8T Sport with 150Bhpit boosts at 7psi which is standard but i decided i was going to bypass the N75 valve in the normal method and use a MBC to control the amount of boost (Typical Scots lad trying to get the speed of a horse from a donkey) coming through in order to maybe gain a few horses and reduce turbo lag and spool up time. So i detached the two pipes from the turbo and wastegate and left the N75 plugged into the Air intake pipe (the longer of the three legs on N75) with the cable plugged in so the car thinks its still in control of my boost. Now being a dumb *** i did this bit then went into my house to put some tools away and then locked myself out with only the car key in my pocket and no tools etc to get back to finishing the job. Yes i did...i can hear you asking already, i drove the car down the 3 miles to the mrs work to get her keys, and yes the 2 pipes were still disconnected from everything.

NOW WE GET INTERESTING.... So the car went like it could pull the world and spin it the wrong way. I hit 18psi without trying and it went like stink (fast) but then it cut out and dropped the boost into -20 in vac (limp mode i guess) but continued trying to boost immediately after until 18-20psi and continued this constantly unless i drove like i was 95 years old.

ok so i got my keys and back into the house to find out i cant find my MBC!!! Aaaargh..

i had another bright idea, so i thought. i will just connect a direct pipe from one pipe to the other so it will boost max until i get another/find MBC. did it but it would only boost to 3-4 psi????

Okay, THE QUESTION IS....When i fit the MBC if i open it up to try and get as much boost as i can will it work or will it not?? sounds daft i know but i figure that when wide open on mbc it should give max boost ie let all pressure through but when i did this with direct pipe it only boosted 4psi max yet when pipes discon it boosts about 20psi max..

Any ideas or am i just being thick????

 

You should never under any circumstances drive a car with no regulation hooked up to the turbo. Not to mention you didn't say what year your car is. If its a Pre-2000 you probably shouldn't even be running an MBC because your engine management can't compensate for the added boost, a 2000+ 1.8T equipped with a MAP sensor can.
You also probably hit limp mode if you went over 15 psi, so now you have to erase the fault code or its only gonna run around 2-3 psi.

 

yeah i figured that but i was needing back into my house and didn't fancy the long walk in the rain, it maybe summer but its damn sure not hot here,its a '96 it hits 16psi before going into limp mode but i have VAG COM software program available at any time to clear faults. Stupid idea yes, cold and wet, Nope. Fitted by MBC today and it runs like a dream. Set to pull at 14psi so as not to hit limp and i dont mind if it falls apart too much as it cost me nothing to get the car and it has a nice 160k miles on it now anyway so will probably die soon anyway.

Will have to hook it back up and look at running stats to check not too lean etc now i guess. It does get treated to 100 Octane fuel when it visits the petrol pumps though.