Do to the overwelming pm's and aol im's, I will take the time to make a how-to thread. I previously refrained from doing this because when i joined here, everytime the word diode came up the words "blow up" and "get a chip" keep coming up. But now since my car has been running strong with a diode for a full year, this has now became more accepted.
This is a simple procedure that will extract more power out of you car for very little cost. I would recommend this to those of you that are either short on cash and still want more power before buying a chip or to those like me that have bigger plans in the future and dont want to spend $500+ on a chip just to need to change it again for the larger turbo.
THIS IS TO RAISE THE BOOST TO A SAFE 16-17PSI ON A 3BAR FPR AND NO MORE THAN 18-20PSI WITH A 4BAR (USE AT OWN RISK)
a 4.3v 1w zenner diode
a mbc or ebc (i recommend a bleed valve for the small stock turbo for smoothness)
a boost guage w/ vacuum guage (which you should have anyways)
4 bar fpr (fuel pressure regulator) not needed but is recommended for anything over 17psi (the ecu will add and subtract fuel as needed)
Soldering iron and lead (or some other way to connect the diode to the map wires)
wire stripper/clippers (to peal back the wire cover)
The first thing you will want to do in this process is to install the boost gauge. If you have one or know how to install one please skip on down. The reason is to make sure you know how to read and understand the boost level of your car.
180 = 11psi
225 = 14.5 psi
The best place to start is to install the end of the line to the FPR. Take a little peice of vacuum hose to connect the top of the Tee to the FPR and then the stock line to the bottom of the Tee and the boost gauge line to the side part of the Tee.
Then run the line to the following grommet below. Poke or cut a hole to allow the hose to slide through (TIP with a wire coat hanger trimmed to about 10-12" inside the vac hose makes it much easier).
Connect the vacumm line to the boost guage (trim as much of the excess line off as possible) and make the power connections to either a accesory power source or a light switch (personal preference) and of course the ground.
First remove any/all engine covers in the way (dont you just love the red engine cover and the polished BOV?) and disconnect the battery. Please make sure you have the radio code first so you dont have to listen to silence for awhile.
then you need to find the map sensor. It will be attached to the intercooler under the throttle body.
pic on my 180
The map sensor wires are in the plastic loom that is connected to the thorttle body hose. You can see the little ring were it clips to throttle body hose in the pic below. The loom will contain three wires 1) purple and grey wire 2) purple and green wire and 3) orange and blue wire. The two you need are the purple/grey and orange/blue wires.
After identifieng the two wires, you then will want to strip the wire covers back to expose the wires. Next trim the diode down as far as you feel comfortable using and bend the sides down so the diode can be hidden better. Then solder the diode inbetween the two wires connecting them. After making sure the wires do not touch reconnect the battery and start the car. If the car starts and idles fine you are good, if it stumbles you have the diode in backwards and need to flip it and try again.
After the diode has been installed correctly, tape everything up to keep the wires from touching. Also you may want to leave the tip of the diode exposed to allow airflow to the diode.
Then go for a drive. Everything in the 180 should be the same with the n75 still installed (may spike a psi or 2 higher). Not sure how a 225 will react since it is over 11psi already. A 225 may have in increase in the boost of a few psi since the ecu is only reading 11psi and requesting 14psi. After everything checks out it is time for the mbc install.
YOU MAY WANT TO DISCONNECT THE BATTERY AGAIN IF YOU DONT HAVE A VAGCOM CABLE TO DO A THROTTLE BODY ALIGNMENT
. To do this you need to let the ecu reset (disconnected for ~10mins) and then reconnect the battery. You then go into the car and turn the car ON and not start it. You will then hear a high pitched whinning noise from the tb. Wait till it ends (few mins) and then start the car. You are done.
There are so many varieties of mbc and ways to install it in the 1.8t. I prefer to remove the n75 from the equation and run just a mbc. Some have prefered to run the mbc before the n75, so the install will be up to you. It really depends on the MBC and which way is smoother to you. I will cover both.
First thing you will want to do is make sure your mbc is setup correctly. Ball and springs need adjusted until you cant hear the ball moving inside the controller anymore and bleed valves just need closed all the way. After the MBC has been adjusted you can install it.
N75: THE PATH IS FROM THE INTERCOOLER PIPING TO THE N75 TO THE WASTEGATE. BEFORE THE N75 WILL BE FROM THE INTERCOOLER PIPING (NEXT TO THE DV RECIRULATION PORT/MY BOV AND CAN BE SEEN IN THE COVER REMOVAL PIC) TO THE N75.
Replacing the n75:
For this method just remove the hoses from the n75 and install them in the MBC and you are done. Just make sure you have it in the right direction, if it is backwards you most likely will be runing off the wastegate (~5psi) and if correct you will be near what you had before depending on how the mbc is adjusted.
Before the n75:
You will need to disconnect only the hose from the intercooler piping side from the n75 and mount the mbc where ever you want it. Then run a vacuum line to connect the mbc to the n75 and you are done. I dont have a pic of this but it is simple enough. Same is above for if the mbc is backwards.
Adjusting boost levels:
Finally the hardware is installed and you will just need to set the level you are comfortable with. 16-17psi is safe on stock fueling with a 3 bar. For 18-20psi you will need a 4bar FPR to be safe
. If you have any worries, a 4bar can be installed at any level of boost and will not hurt or harm performance. It may take a few cycles for the ecu to adapt to the added fuel but will not be really noticable when installed.
Just work in small increases to get to the desired psi. Go through differnt types of loads to make sure you dont peak to high in differnt loads. Once set, you are finished and able to enjoy the new found power increase.
As always I am available for questions either in this thread for all to see or in private via pms or on aol.
should look like this without the n75 being used