# 12v vs. 24v wiring harness



## deathmetalscottie (Jun 4, 2007)

Any differences?
Could I theoretically swap in 24v VR in place of the old 12v, leaving the cars stock management? aka plug an play, so to speak.
My buddy wants to drop in a 24v in place of the 12v in his GTI. 
Edit: just thought of something, he has an '01, did this year come with drive by wire? 


_Modified by deathmetalscottie at 11:24 PM 4-17-2009_


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## apstguy (Apr 3, 2006)

All MkIV VR6s were drive by wire. The harnesses are different such as a 24V VR6 has variable valve timing so it has extra sensor and solenoids on the cams. Also the ignition system is very different. Not just plug & play.


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## vwmaniac16vr6 (Nov 17, 2004)

*Re: (apstguy)*

the car will run off a 12v wire harness you just won't have vvt. i just put a 24v into a mk3 and ran it with 12v management and it runs great just dosn't have vvt


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## deathmetalscottie (Jun 4, 2007)

*Re: (vwmaniac16vr6)*

ok I'll admit it, I want the 24v in my car. 
also forgive any seemly stupid questions as I'm a mk3 12v guy








anyway few questions.
1. I want to put the ENTIRE (at least most of it) mk4 harness in my mk3 as it would stream line pretty much everything in the car, a lot less splicing, when I put the mk4 dash into the car. Will the interior harness support the 24v engine harness when I get around to upgrading? I'm just wondering how "modular" the harness actually is.
2. how is the vvt controlled? reason I ask is, I plan on going down the megasquirt path in the near future. I know that it doesn't support vvt per say but it can be setup to support it. 
3. how much extra power, if any, does vvt give the engine? If it dosen't make a huge difference in power, I might just say f*ck it and not even bother.

_Modified by deathmetalscottie at 5:12 PM 4-18-2009_


_Modified by deathmetalscottie at 5:13 PM 4-18-2009_


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## RipCity Euros (Sep 23, 2007)

*Re: (deathmetalscottie)*

I think you would need the "extra" version of megasquirt to control the VVT. You basically need a PWM output.

_Quote, originally posted by *deathmetalscottie* »_Will the interior harness support the 24v engine harness when I get around to upgrading?

What?


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## deathmetalscottie (Jun 4, 2007)

*Re: (RipCity Euros)*

there are two parts to the cars wiring harness, the engine bay section and the cabin section. Will the engine half the harness be compatible with the 12v interior side of the harness? On mk3s, depending on the year, the interior half of the harness will not always be compatible to the engine half when swapping in a VR6.
Another example would be: I have a 2000 Golf and I want to swap to a 24v VR6 from the 2L. I pull the 2L's wiring from the engine bay, but leave the wiring in the cabin alone. I then plug the VR6 engine bay wiring into the relay board. Will this work? as long as both pieces of the harness are compatible, it should work.


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## RipCity Euros (Sep 23, 2007)

*Re: (deathmetalscottie)*


_Quote, originally posted by *deathmetalscottie* »_there are two parts to the cars wiring harness, the engine bay section and the cabin section. Will the engine half the harness be compatible with the 12v interior side of the harness? 

No, it will not be. There are five 6-10 pin colored plugs (White, brown, black, blue, and orange) on one of the *TWO* engine harnesses that need to go to the interior harness, aswell as a 14 pin one, and a 4 pin one. They are in no way compatible with MK3 wiring, they will either need to be spliced in, or plugged into the MK4 interior wiring.

_Quote, originally posted by *deathmetalscottie* »_Another example would be: I have a 2000 Golf and I want to swap to a 24v VR6 from the 2L. I pull the 2L's wiring from the engine bay, but leave the wiring in the cabin alone. I then plug the VR6 engine bay wiring into the relay board. Will this work? as long as both pieces of the harness are compatible, it should work.

Look at these 7 plugs in your golf that i listed above (well actually 6 because one goes directly from the engine bay side to the DBW gas pedal), if they plug in, then it SHOULD work.


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## deathmetalscottie (Jun 4, 2007)

*Re: (RipCity Euros)*


_Quote, originally posted by *RipCity Euros* »_
Look at these 7 plugs in your golf that i listed above (well actually 6 because one goes directly from the engine bay side to the DBW gas pedal), if they plug in, then it SHOULD work.

sorry for the confusion, I was using this as an example. The mk4 wiring harness will be going into my mk3. Ok as long as it will work, I'll just buy up a mk4 golf harness, and mk4 12v engine harness, ecu, and stuffs. Then when it comes time to put the 24v in, I'll have a 24v engine harness and megasquirt ready to go. 
Question, can you guys direct me or gimme a link to where I can get a little more information on running the vvt through the megasquirt. There has gotta be someone on the tex' who has done it.


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## RipCity Euros (Sep 23, 2007)

*Re: (deathmetalscottie)*


_Quote, originally posted by *deathmetalscottie* »_
Ok as long as it will work, I'll just buy up a mk4 golf harness, and mk4 12v engine harness, ecu, and stuffs. Then when it comes time to put the 24v in, I'll have a 24v engine harness and megasquirt ready to go. 


Okay, maybe my reading comprehension is off today, but why would you get a MK4 12v engine harness, ECU etc.? If your car currently has 12v managment, you should be able to run the 24v off of that if you so choose to go that route.

_Quote, originally posted by *deathmetalscottie* »_
Question, can you guys direct me or gimme a link to where I can get a little more information on running the vvt through the megasquirt. 

This may be helpful
http://forums.vwvortex.com/zerothread?id=3090118
And you can try the SEM forum, but remember to search first.
http://forums.vwvortex.com/zeroforum?id=517


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## need_a_VR6 (May 19, 1999)

*Re: (RipCity Euros)*

It will depend on the year, the cam sensor changed on the 12v when it went to single chains to the one that is like the 24v (multi tooth). You'd need to make sure you use the ECU/wiring/sensor from a later car. 
Standalone is a whole other game though. MS can run the VVT solenoid using the boost control output but from what I can tell it needs quite a bit higher frequency then the MS can deliver, and requires a special circuit to double it.


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## deathmetalscottie (Jun 4, 2007)

*Re: (RipCity Euros)*


_Quote, originally posted by *need_a_VR6* »_
Standalone is a whole other game though. MS can run the VVT solenoid using the boost control output but from what I can tell it needs quite a bit higher frequency then the MS can deliver, and requires a special circuit to double it.

That I have heard. Also, I wanted to be able to use the boost control output but I think that I can get a daughter card that supports a higher level of boost, something like up to 30 psi ( not that I cwould ever go that high







)

_Quote, originally posted by *RipCity Euros* »_
Okay, maybe my reading comprehension is off today, but why would you get a MK4 12v engine harness, ECU etc.? If your car currently has 12v managment, you should be able to run the 24v off of that if you so choose to go that route.


1. I'm swapping a Mk4 dash into my car. I it should stream line the whole wiring process making it much easier in the long run.
2. True I could run a 24v engine off of the stock management however, I would lose vvt which I want to keep that functionality.
3. True I could add support later into my current harness for vvt but the mk4 24v harness is already wired for it. Making the connection to the ECU all that less complicated. 
4. If I use the Mk4 12v harness now and have the mk4 interior harness piece in the car, all I have to do is swap the 24v engine harness at installation. 
Also thanks for the links dude and bearing with my slight "nubbiness".


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## need_a_VR6 (May 19, 1999)

*Re: (deathmetalscottie)*

The MS boost control feature isn't as nice as a good electronic boost controller, at least not yet. I would just run MBC and use the MS output for the VVT. I've run 4bar MAP sensors on a few cars, good for 43psi, the 3bar GM ones are good for 30.


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*

ok i just looked on the diytune.com website and the new msII pcb apprently supports PWM. does this mean that the ecu has built in support specifically for vvt? http://www.diyautotune.com/cat....html
looks like it actually does!


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## need_a_VR6 (May 19, 1999)

*Re: (deathmetalscottie)*

There's no native support for fully variable VVT, everything is very experimental at the moment. If you see PWM mentioned, it's for the idle valves.


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*

ok I see. reading the "fine print" over again, yeah... Meh I guess running vvt through the boost single and running an MBC would suffice. But being able to fine tune everything from the cabin through megatune would be nice though.


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## need_a_VR6 (May 19, 1999)

*Re: (deathmetalscottie)*

I don't understand how people can NOT want to be able to fine tune everything at this point


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*

is there anyway to connect some sort of electronic boost controller signal to the megasquirt. possibly someone has done a mod to add this in separatley from the already built in controller. I could have sworn that there was a daughter board that came with a better boost controller.


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## need_a_VR6 (May 19, 1999)

*Re: (deathmetalscottie)*

There is the option for the built in boost control, BUT I've never gotten it to work closed loop and it's the same controls you steal to use for the VVT. Unfortunately there aren't many hardware PWM outputs on MS1/2.


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*

I wonder, would it be possible to run the stock 24v ecu in parallel with the megasquirt? The stock ECU would control any non fuel or spark functions, plus VVT and drive-by-wire. Then the megasquirt would take over both fuel and spark. The only question I have is, would the megasquirt have some control of when VVT activates? Also, does this seem a little too complicated? I mean is drive by wire really that important? Can it be controlled through the squirt? 


_Modified by deathmetalscottie at 9:55 PM 4-21-2009_


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## need_a_VR6 (May 19, 1999)

*Re: (deathmetalscottie)*

It might be possible but I'm not sure what the stock computer would do with the DBW/VVT if the injectors and coils are not plugged in. Certainly possible though. 
If you use the stock ECU for VVT, MS would have no control of it. 
For the DBW there's no way for MS to run it, and there are no plans to add that support. I built a small proto setup to drive the DBW tb with a microcontroller and having done that, I can see why no one wants to sell one.


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*

I see. In my opinion, it seems like a good idea to use both in parallel for this setup but seems more feasible to just run non-engine management controls for the stock ecu and the ms for everything else. It's not like couldn't run by a good ol' throttle cable instead right? I think what I'll probably end up doing is finding an electronic controller somewhere or fabricating some sort of valve system that will allow me to fine tune a MBC from in the car. Just would have been nice to tailor the boost controls to my custom map.


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## Zupek (May 10, 2000)

*Re: (deathmetalscottie)*

I am not reading all of this crap, but I run 12v software on my 24v and have for a long time. You wont have VVT or the Chang over Valve for the intake manifold (can easily be doable though) if you have any more questions PM me and answer the best I can.


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## deathmetalscottie (Jun 4, 2007)

*Re: (Zupek)*

Zupeck:
The original plan was to go with megasquirt not stock management. In fact, the 24v engine would never see 12v management. I just wanted to know how compatible the interior half of the mk4 12v wiring harness was to engine half of the 24v for wiring simplicity.
Need_A_VR6:
Ok I kinda slept on the parallel ECU idea. 
DBW:
Correct me if I'm wrong but the only difference between DBW and a standard throttle cable is how it's controlled. One mechanically, the other electronically correct? Well, if the DBW's functionality is to only open and close the butterfly plate in the throttle body based on the gas pedal depth. MS should be fine not controlling this. 
VVT: 
This was a little harder to figure out so I'm basically going to tell you what my goals are for my little project and possibly this may help. My plan is to build then engine and run a custom Vortech V2 setup. The hp goal is 450 bhp which seems a little more realistic for higher hp gains. Originally when I was going to go with a 12v setup I was going to get a set of Daugherty cams. But with the decision to go 24v and VVT, I'm not exactly sure what to go with. Do you really need to control when VVT actually fully kicks in? I mean, you should be able to customize your map for the higher cam profile and tailor it for when VVT fully kicks in right? I know VVT starts working after 1200 RPMs, what RPM does it reach it's peak?


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## Zupek (May 10, 2000)

*Re: (deathmetalscottie)*

Well the VVT is actually Varialbe Cam timing, which actually just takes the intake cam and advances based on knock(I believe). I am not sure there is a linear path in which the VCT actually engages, but don't hold me to that.
When I looked into what it would take to gete the VCT to work on 12v management, the long story short was, you needed the 24v fuel management, which isnt going to happen. 
I asked a VW tech (hoping they would actually know) and the old dude told me, the solenoid (which is just oil pressure switch) kicks on and off multiple times within the RPM band based on certain criteria, so you may be screwed on advancing the timing on the intake cam (which, btw you dont actually need)
As for DBW, it actually is completely different then DBC, the software is completely written different as well, its not as simple as saying "well this voltage from the pedal means the butterfly should be open X ammount, which was this fueling on the DBC"
Please if someone knows different feel free to correct me


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## need_a_VR6 (May 19, 1999)

*Re: (Zupek)*

For the parallel ECU the DBW from the stock computer will work, only as long as unplugging the injectors/coils from the stock ecu's control doesn't do something stupid.
The intake VVT is fully variable over a range of 52deg (crank). It uses closed loop correction of a PWM output to get the desired advance. There is some sort of load/rpm map for desired cam angle. The way it gets controlled is varying oil pressure through a solenoid that diverts from one side of the cam gear to the other (varying it's position relative to the cam). 
Here is good info on how the advance is mapped on a chipped R32: http://forums.vwvortex.com/zerothread?id=4051402 compiled from some logging Powerdubs did for me. 
The cam is advanced mostly in the midrange, with it being at lower advance at low and high rpms and load where overlap can be detrimental to power and emissions. 
For max power you probably don't need it, but it can buy you some midrange.
Hope that helps a bit.


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## RipCity Euros (Sep 23, 2007)

*Re: (need_a_VR6)*


_Quote, originally posted by *deathmetalscottie* »_Correct me if I'm wrong but the only difference between DBW and a standard throttle cable is how it's controlled. One mechanically, the other electronically correct?

Mmmm not really, the DBW system takes in inputs from:
-MAF
-Speed Sensor
-Camshaft position sensor
-Both 02 sensors
-Throttle control valve
-Intake air temp
-Coolant temp
-Knock sensors
-Gas pedal position sensor
-ABS system
It determines how much torque is being made, and how much is requested/ it (ECU) wants to make and sends this demand to the output components:
-Throttle body
-Injectors
-Coilpacks
-Etc.
So it basically takes the driver inputs, calculates how much torque is needed and attempts to fufill the request. When you step on the throttle, it is essentially a "request" not a demand. 

_Quote, originally posted by *need_a_VR6* »_only as long as unplugging the injectors/coils from the stock ecu's control doesn't do something stupid.

Good luck, this managment is picky.


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## deathmetalscottie (Jun 4, 2007)

*Re: (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_For the parallel ECU the DBW from the stock computer will work, only as long as unplugging the injectors/coils from the stock ecu's control doesn't do something stupid.
The intake VVT is fully variable over a range of 52deg (crank). It uses closed loop correction of a PWM output to get the desired advance. There is some sort of load/rpm map for desired cam angle. The way it gets controlled is varying oil pressure through a solenoid that diverts from one side of the cam gear to the other (varying it's position relative to the cam). 
Here is good info on how the advance is mapped on a chipped R32: http://forums.vwvortex.com/zerothread?id=4051402 compiled from some logging Powerdubs did for me. 
The cam is advanced mostly in the midrange, with it being at lower advance at low and high rpms and load where overlap can be detrimental to power and emissions. 
For max power you probably don't need it, but it can buy you some midrange.
Hope that helps a bit.

that is exactly what i need! thanks for the help. this should get me going in the right direction.


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