Vct Issues

[Grant Smith]

hey so this is my first post here on skylines au. im from canada and ive been trying to figure this one out for months now and nobody over there can figure it out so hopefully one of you guys can help me out with your wisdom!

okay so heres the problem:

i had an rb20det in my s13, then blew the head gasket on that motor, so i went and got and series 1 rb25det motor. i swapped that one into my s13 and its running great, but missing some power so i go to figure out how to hook up the vct. im still using the 5 speed rb20det wiring harness, and am using an automatic rb25det ecu series 1. since the rb20det doesnt have vct i read the wiring diagrams, and added a pin to the harness on pin 113 for the vct function. i ran that wire to one side of the vct solenoid, and the other wire on the solenoid to switched 12V. but the vct still wont function. i meter out the soenoid harness and i get 12v swtiched on one side, and no ground continuity on the other, ive tried it as im driving, idling, reving, but still no ground coming from pin 113. i opened the ecu and metered the circuit board to the solenoid plug and there is continuity so i know the pin is connecting. at first i didnt have a neutral sensor hooked up but i read i needed that so i wired the neutral gear switch pin to ground so the ecu always thinks it is in gear, but it still will not make vct turn on. i have a speed sensor connected aswell and still nothing. i tried a 5 speed ecu aswell but it didnt change anything. i cannot figure this out please someone help me i am about to throw my rb25 off a bridge because i am not getting anymore power than what i already had with the rb20!

[Moodles2]

VCT won't function until the engine has reached a minimum temperature, is the coolant temp sensor functioning?

[Grant Smith]

ill go check that out today, i dont have any other symptoms of a bad coolant temp sensor but ill check anyways thanks for your input!

[Stevoss]

get a msd window switch

[Grant Smith]

i was thinking about doing that but i also considerd that the ecu should know when its in vct modes because shouldnt it affect the fuel and timing maps? i wouldnt want to enable vct without the ecu knowing about it

[Dasmbo]

I have seen a shift light converted with a relay to switch the vct and it was ajustable with the shift light control you might want to try that or a rpm switch could also be a lack of an earth somewhere in the loom

[GTSBoy]

If you don't have the speed signal fed to the ECU correctly then you won't get VCT either. I have heard scuttlebut that the speed signal that is output from the R32 dashboard is not compatible with the RB25 ECU, so I would hazard a guess that if this is true, then it would also be true for the S13.

[Grant Smith]

hmmm that actually might be it... cause im using an r32 tranny....

[paulr33]

dont forget NTR must be OFF for VCT to fire

ie if your in nuetral or you havent wired in the NTR switch, the VCT wont engage

from memory

#DEFINE VCT 1

func main(void)

{

if(RPM < 1800 && ! switch(NTR))

{

func(VCT);

};

return;

};

i dont think its speed related at all ?

[DVS JEZ]

Just hardwire the vct to see if the response is better.

If the vtc isnt wired in it wont affect top end power.

What boost are u running and what power is it making?

[Grant Smith]

its making about the same power as my rb20 did. definetly not a noticeable gain. and yes i have the neutral sensor pin grounded so it always thinks its in gear.

[KiwiRS4T]

Apply power to the vct solenoid and earth the other side to see if it is working or not.

[Grant Smith]

yes the solenoid is working it has 12v, and i can manually ground the vtc pin and it will enable to solenoid and the idle will change, i was messing around with my friends series 2 rb25, and he dosnt even have a speed sensor on his car, and it still works, i unplugged his coolant temp sensor and vtc still works, the only time i can get it to not work is when i unplug his tps, but its a different tps than mine cause im series one. so it has a different plug i can just swap them to see if it makes a difference, i tried a different ecu in it and still wont work, and tried a z32 ecu in it and it wont work either

[Guilt-Toy]

does the ecu get the speed signal from the speedo and the speedo get the signal from gearbox?

thought it would be the other way around?

anyone know the pin outs? need to get it working on the r32

If you don't have the speed signal fed to the ECU correctly then you won't get VCT either. I have heard scuttlebut that the speed signal that is output from the R32 dashboard is not compatible with the RB25 ECU, so I would hazard a guess that if this is true, then it would also be true for the S13.

[Grant Smith]

in my s13 the signal goes to the cluster, and then to the ecu from the dash plug.

k i think i have found the issue here... when i put my greddy intake plenum on my motor i had to extend some plugs for aav, fcid, and tps... there was a second tps plug and i read to cut it off cause it was for the automatic gearbox... but i was going through the ecu schematics and i found something called a throttle valve switch, that isnt the tps... so i did more research and apparently it uses the same plug on the tps that the auto gets the signal from. i figure finding this plug and hooking it into the tps will make my ecu happy and turn vct on =)

ill find out tomorrow hopefully it all works ill be the happiest rb25 owner ever

[honan]

If not, the msd window switch, or nos rpm switch, vct controller etc is a good option.

I had an issue in my r33 where the stock ecu would not control vct properly, after a turbo and fuel upgrade I got a nistune on an rb20det ecu and use a nos rpm switch for the vct, works better than it ever has.

[Grant Smith]

ALRIGHT VTC IS FINALLY WORKING!!!!! after so long messing around with it i finally got it to work! so series 2 rb25det uses the tps to sense when it is off idle and will kick in the vtc, but SERIES 1 dosnt! it has a "throttle valve switch" that uses the same socket as the automatic tranny tps plug. so the 3 pin output on the series 1 tps needs to be connected to sense that the motor is off idle and therefore making the ecu happy to turn it on. so i wired pin 57 and pin 54 to this socket and voila! vct solenoid clicks when i tap the gas =) thanks everyone for trying to help me out i very much appreciate it!

[JonnoHR31]

does the ecu get the speed signal from the speedo and the speedo get the signal from gearbox?

thought it would be the other way around?

anyone know the pin outs? need to get it working on the r32

speedo drive => cluster => ecu.

on the ecu side on a 33 its a green wire with a yellow trace iirc, 32 should be the same. not sure on compatibility between models though if your running a rb25 etc

[RRob]

Earthing the neutral pin is incorrect also. The input drop's to earth when neutral is used therefor disabling vct.

[Grant Smith]

Earthing the neutral pin is incorrect also. The input drop's to earth when neutral is used therefor disabling vct.

no earthing the neutral pin is correct, when the car is in any gear the neutral sensor senses ground, and there is no continuity when in neutral, so rather than having my timing pulled around when going in and out of gear, i just grounded it to make the ecu think its constantly in gear.