I am in the process of grafting a Nissan RB25DE wiring loom to the Holden VL loom and following the Nissan circuit diagram the air conditioning & FICD control is done through the ECU. What I want to know is if anyone has done this and used the R33 ECU setup to run the VL's air conditioning system? Has anyone done an RB20/Rb25/Rb26 conversion into a VL and ran the engine without any signal input into the ECU from the air conditioning?,does the engine run o.k. without these signal inputs whilst running the air conditioning? The Rb30 computer has a signal wire from the aircon circuit running to the ECU telling the computer when the A/C is on,the R33 setup has 2 wires,1 controlling the FICD solenoid and 1 controling the aircon relay,the thing is there is a box which the ignition signal Tees off into,along with another wire from what looks like the Skylines climate control on the circuit diagram,another wire comes from this box and goes into the ECU on the earthed side of the FICD relay coil,which then goes into the ECU,as far as I can gather this is the signal from the climate control which tells the ECU to switch the A/C relay on,can anyone confirm this?

Hey Just a thought. Did you have aircon before your conversion? If you did then keep it wired and put the old air con pump off the rb 30 block straight on the new engine, Should bolt straight on, same block. Just an idea, you prolly thought of it though Tim

Oh this would also mean that if it does use the ecu then youll have to keep the old one. I still dont see why you need your ecu though. Tim

I haven't completed the conversion at this stage,I am still grafting the wiring loom up to the VL loom which I had spare from my last VL and I am still waiting on piston rings , the AFM and the injector wiring harness which is taking ages for the importer to get,the wiring loom alone took nearly 1 month after I bought the motor. Also as funds permit I have to get the flywheel remachined and a new clutch kit,also I would like to do up the tailshaft and fit a rebuilt differential with rear discs but I have to lay off spending for a while because it has nearly sent me flat broke doing everything at once. I just need to know what the part with 3 wires going to it does,is it a thermostat?,I am using the R33 engine management system and the existing aircon system on the car,I just have to figure out what that device is on the wiring diagram as I cannot read in Japanese.

What I should be asking i guess is what is the aircon signal for and how does it affect the operation of the ECU. I know I am not using the idle up power steering pressure switch input as the VL never needed it so I don't see why it will need it now. THe old ECU however,does use an aircon signal input,I know in the manual and auto VL's the neutral signal is fed back into the ECU via a neutral mode sensor,but I now Guido Seevens who has an RB25DET fitted into his VL doesn't even use that and with no problems,I am but. I fugure it may run without the aircon input but I don't want it to be like the older Carby powered Commodores where you had to switch the aircon off to overtake as it took power off the motor ,maybe it is a signal for the ECU to inject more fuel,that is what I need to know.

Hey, I think if u don't connect the a/c signals to the RB25 ECU it will be fine. Just set it up like the VL was originally with the a/c switch turning on the a/c relay which powers the compressor clutch and FICD, not computer controlled. I don't think u'll notice a difference! I don't think the RB30 ECU did anything with the a/c on signal except generate a fault code! the RB25 ECU is sure to be different but if it does something funny just deal with it then! I would say it is to do with climate control which u don't have 8) Cheers.

Like twin vl said, just connect it up without the ecu. I was told my gearbox needed original ecu but it doesnt use it and i get all 4 gears no probs. I have a rb25 wiring diagram which i think is mostly in english so i'll have a look around for it for you and post it. Maybe it will help. Tim

http://www.meggala.com/rb25detenglish.html This is the address of that diagram, if it doesnt work let me know. Tim

The aircon system in the VL isnt entirely needed .. it only affects IDLE .. it doesnt affect anything once your above idle as far as I can tell by my experimenting. (Done some re-wiring/changing the way aircon is switched on/off). The signal to the ECU is just to tell it to raise the idle so the car wont stall/sag electronics too much when aircon is on and your idling. Its just a High/Low state from the switch .. when its +12, the ECU raises injector pulse width slightly at idle, and the wire also goes to the FICD which allows a little more air through. If you enage aircon without the FICD or ECU raised, aircon still works, it just drops my idle from ~650 to ~450 .. almost stalling point, but it still works. IT makes no difference once driving, so it wont affect overtaking potential, etc.

I thought the idle control was done by the FICD solenoid valve,that section is a piece of you know what to wire up,the way I saw it was the FICD solenoid bypasses the throttle body butterfly and when opened allows more air to flow through causing the airflow meter to sense the greater amount of air flowing through thus increasing the idle speed. I am in the electrical trade and wiring the aircon up is a snack,but it was just knowing what that wire actually did on the RB30E computer,from memory now the VL's ECU does have a fault code for its aircon so as twinVL mentioned it is most probably just a signal wire to tell the ECU if the aircon is working or not,it it pretty useless really as it will be obvious if the aircond doesn't work. So it sounds like the aircon has nothing directly to do with the computer in the VL,so I will keep it running as it always has done minus any input into the ECU,the R33 does actually actuate the aircon through the ECU but I will retain the standard setup which the VL has.

Its not a fault signal wire as such, its in the holden service manuals, its a +12 hardwired directly to the switch on the dash. The dash switch switches +12v to 3 places, 1 direction goes to the ECU, and raises the injector pulse width, while the Throttle Position sensor is closed (so only at idle), another goes to the FICD solenoid, to allow more air to enter (to keep the mixture balanced), and the 3rd goes to the aircon system itself. The fault code is of course canceled by switching the aircon on and off, and this is all teh fault code tracks, if it gets a +12 on that pin or not. I'd say in your case your right, its fairly useless and not worth hooking up. Just wire the dash switch to the aircon itself. I've done the experiments btw .. FICD but no +12 to the ECU does *NOT* raise the idle. See my other thread a few weeks back about faking aircon engagement, I used the FICD (without aircon compressor engaged) to raise the idle. +12 to ECU only - Nothing +12 to FICD Only - Nothing +12 to ECU + FICD = Raised Idle +12 to Aircon Only = Aircon, very low idle +12 to Aircon + ECU + FICD = Aircon on, and normal idle

Just another thought Russel, Maybe the r33 ecu actually switches the a/c off on full load or like limp home mode or something?? And Load-data, If u supplied power to the FICD only without the AAC valve hooked up u'll find it increases the idle speed quite abit! The AAC valve compensates for the FICD opening. Yeah ECU prob does richen the mixture slightly cos the airflow through the AFM is prob too small to register the change! Only on idle.

I just used the wiring the way it was .. on LPG just opening the FICD is all I need Some original photos have not been recovered yet.

If you pull a VL loom apart which I have done that signal wire isn't connected to the dash,the only wire thay is near the dash is a wire coming from the climate control,then goes into one of the connectors near the ECU then goes up through the pressure switches then 3 wires go off from that to control the FICD solenoid valve,the A/C compressor clutch then the other is the signal wire back to the computer. The VL's aircon circuit is not controlled by the ECU as I figured out,more like the aircon circuit controls the ECU in a way,the signal wire is pretty useless and only tells the computer that a fault has arisen in the A/C circuit,but a monkey can tell if there is a fault in that circuit without the ECU telling it there is. As for the R33's aircon control,would be nice to know how it works but someone off the performanceforums website has wired his RB25DET powered Skyline without it and it works fine,I think it may just be some emission control crap or a way of making more money by telling the customer they need a new ECU if it A/C goes Kaput because the ECU had a fault in it,I believe this isn't necessary.

a lot of newer cars switch the ac off at full throttle so maybe that has something to do with the extra wires on the R33. The FICD raises idle when the ac is switched on so thats what the signal from the ac to the ecu would be for on the VL.

Just for interest sake I noticed you come from Newcastle. I live about 15 kms north of Raymond Terrace.

yeah i'm actually from cessnock but i figured the people on the other side of australia wouldnt have a clue where that was.

My info says i'm from mt.eliza, vic .. but i'm currently living with my GF in Newcastle area .. Glendale/Argenton area Some original photos have not been recovered yet.

newy people evrywhere - either of you guys going on the anzac day cruise??? if not we might need to have a gathering in newy at some stage in the future. How long you hanging around for Lord-Data???

Heheh I'm not plannin on going anywhere .. so should be around for a long time That pic in my avatar was actually taken at speers point, for reference If you see a gold vl with vic plates around the area, ya know its me Some original photos have not been recovered yet.