HOWTO: RB25DET High Boost mode with standard solenoid

Intended Audience: Stock RB25DET owners
Technical Level: Very Easy
Duration: 5 minutes
Effort: Easy
Result: Fairly Good

!!!Caution/Achtung/Attenzione!!!
Follow this guide at your own risk. You have been warned. We are not responsible for any actions you take. The instructions contained herein are only a guide and should be done with caution, If you doubt see your local mechanic. If you are unsure or are not confident don't do it.

Background:

As you all know the standard R33 RB25DET boost solenoid (value controller) is 5psi until rpm is greater than 4500rpm and then its 7-8psi. Continue reading if you wish to always be in high mode (7-8psi). If you have an aftermarket boost controller then you can stop reading now.

The standard solenoid has two wires running two it, one is constant power which is shared with the AAC value and some other components (see wiring diagram) the other is a ground signal. The ground signal (black wire) is run to the ECU. This wire is grounded when rpm is greater than 4500rpm by the factory ECU. Basically if you give the wire a constant ground instead of the ECU's above 4500rpm ground it will always be open, thus allowing it to be in high mode aka 7-8psi.

The mod:

Cut the black wire and run it to your own ground on the car body somewhere. Find a local bolt/nut or metal chassis component and attach a lead wire to it, then run this lead wire the black wire on the standard solenoid. For testing you could run this to the suspension tower, is has a huge bolt/thread on top of it. The other end of the two wires (black and white) should run to the factory harness plug (black odd looking plug), which can be simply taped up so it goes nowhere.

Be sure not to the modify the white one, as it's power for the solenoid.

See new-wiring.jpg for how it should look

Basically the black wire goes to your new ground, the white wire doesn't change. Make sure you tape up the loose end of the black wire out of the plug and don't leave it dangling around. Now to test

Test:

Start up your car, make sure you don't have any alarms or warning lights etc.. Safety is important!. Instead of your car going into 7-8psi above 4500rpm it will be in this mode all the time, this means when you take off in first youll be limited to 7psi instead of 5 and thus applies for all driving thereafter. Take it for a quick spin and see the difference. You'll notice first is whole different feeling to it and each gear thereafter seems to have more stick about it. Your top end power output will not be changed, ie if you made 140rwkw and you've done this mode it will still be 140rwkw it's just the curve will be sharper as you'll be on more boost quicker

Tips:

If you don't notice any different then you've either done the wrong wire or the ground is strong enough. Be sure to pick a strong ground and make sure its secured properly. You can get gold washer clips which will hold a wire and provide a good ground for use on a nut (see the yellow thing in new-wiring.jpg)

If in doubt you can simply unplug the black factory harness plug and your controller will be in closed mode which is 5psi all the time. With only a power signal the solenoid doesn't function and thus it will always be in "closed" mode which is 5psi

Questions?

How does the solenoid work?
The stock solenoid works like this, with power and ground it will be in "open" mode and let through a maximum of 7-8psi. With only power it will be in "closed" mode and will only allow through about 5psi. The ECU makes it go into "open" mode by giving the black wire ground signal which makes the circuit complete. All you are doing by "adjusting" the black wire is making the circuit complete all the time.

What will happen above 4500rpm now that I've done this mod?
The ECU will still ground the wire above 4500rpm but nothing will happen. As long as the black wire is taped up you will be fine. Of course if you are creative you could run this wire to something else and it will be turned on when rpm is greater than 4500rpm. Crap like turn on the water spray kit for the intercooler, flash a light, do some other crap

I've broken something, can I reverse what I have done?
Should you do some damage or have broken stuff you can get a stock boost solenoid from the for sale section of the forums for like $50 tops, as its fairly useless when you have an aftermarket boost controller. The standard wiring is fairly simple, one is ground one is power. You can't have a circuit without both. See wiring diagram if you are unsure or doubtful.

Have fun and enjoy

** Corrected wire colour mistake **
** Corrected 3 more wire colour mistakes lol Duncan **

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can this do any damage at all? Or is it a standard and safe mod?

wil..

no i wouldnt imagin any damage would occur if its done correctly, 7-8psi is nowhere near the capabilities of the turbo/internals. Considering others are upto it, ie fule filter and sparkies, timing etc

dont see how, you run 7psi over 4500rpm anyway. by doing this mod you just make it be like that all the time

sweet....gonna do it today:D:D as for hookin the ground wire to another component u mean the wire thats commin out of the plug yeah that should be taped up rite?? so i just tap this ground wire to the ground wire of the component that i want to turn on after 4500rpms rite??

Did this mod to my car last week after I saw this post. :devfu: Except my ground wire was the black wire?? How to test:- Simply remove plug from solenoid and put the (-) wire of a multimeter on a ground point of the chassis, start the car and test the plug from harness to see which wire has +12V from ECU with (+) wire of multimeter. Once found switch off motor and cut the other wire (which is the ground wire switched by ECU) ON THE SOLENOID SIDE OF THE PLUG and add wire to ground it on chassis. Solder and Insulate bare wires, hook up plug again and enjoy more boost. I also resetted ECU after this and have had no problems. Thinking of adding a switch inside on dash so I can set it so constant power not on solenoid on those long trips between states, might help solenoid from burning out??

TopKart R33: thanks man. im gonna test mine 2nite cause did it the way everyone else said but no difference in boost. I've gotta 94 GTS=25t so likely to be the same as yours.

Dave

there is one small problem with this...

If the ECU happens to go into limp mode, because something is wrong with the engine or sensors, then boost will be limited to 5psi as the ecu wont switch the solenoid on. As its been bypassed, the engine will hit full boost regardless of faults. In limp mode your injector pulse width me be set, meaning that in limp mode, under full boost, you COULD run lean.

Just something to think about.

well in limp mode you cant rev past 2500 rpm anyway. the solenoid is turned on above 4500rpm so you wont get much boost at 2500rpm

I did this today and there is a noticeable difference down low. Also my SII R33 Sedan the wiring was different, the ground was in fact black, so its a good idea to do as Topkart suggested. I also added a switch in the engine bay, and mounted it above the solenoid, as i couldnt be bothered to wire thru to my dash and drill holes to mount a switch.

i have the same .. solenoid for R34 GT-T ... and the ground is the BLACK .... i wanna try this thing ... but i wanna ask 1st ... is it ok to do it with my NEO 6 RB25DET ... ?!


nice work EvilINGT

it should be the same. does the r34 have the same dual stage boost? if so then it shoud be the similar operating method and similar mod method

yeah same here...realised after i hacked it up...haha...oh wells.
just wondering if u could just splice the ground wire and hook it up to a simple on off switch?? would there be any problems with the solenoid gettin a second ground signal from the ecu or any probs with the ecu gettin constant ground signal??
also is there any mixture probs with runnin 7psi down low??

you can make a switch control the ground, so its a grounding switch. would do the same as a simple on off switch

am not sure exactly ... what am sur about ...is that my car go's to the top boost .. befor it reaches 4500 .. at 2500 it can get the top .. and after 4500 it never increas ..

so i unpluged the solenoid ... and tested the wire coming from the ECU... i had a (-) signal all the time even at idle .. so its grounded all the time ..?! .. .. is that normal .. with 1998 r34 gt-t .. ??? ..

You might have to run a new wire from Acc to provide +12V as the ECU may be switching Power wire instead of ground.