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Thread: GQ VH45 V8 Conversion (TB42E ECU > TCU wiring help!)

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    Question GQ VH45 V8 Conversion (TB42E ECU > TCU wiring help!)

    Afternoon all,

    I'm at the end of a months-long conversion saga, putting a 95/96 VH45 into a 95 GQ with an Auto box. I have 99% of the wiring down pat but there's just a couple of items I'm just struggling to complete, specifically the wiring between the ECU and the TCU.

    There's a pretty good set of manuals available on this site thanks to some generous members here and elsewhere that I've had a dig through, and I have the TB42E ECU supplement page, the Haynes manual and the Gregorys manual as well as the OEM manuals for the VH45. Luckily donor and recipient being Nissans of around the same age the design of both systems is pretty similar, and both the VH and TB engines use the same gearbox in their respective cars, although with different TCU's

    Now the problem that i'm having is that the manuals/diagrams for the A/T are for the TD or carby TB and so don't have any info on what inputs it gets from the ECU rather than directly from sensors. TPS and Throttle switch would be two items that are substituted with ECU outputs and that's the way it works with the VH layout, logically there would also be a RPM signal to the TCU and i believe there is a common sensor ground

    So what I need to be able to complete:

    - Ideally, someone has a TCU pinout for a TB42E they'd be willing to share () but this seems increasingly unlikely given the time i've spent looking for such a thing
    - ECU Pin 28 does what? This runs to TCU Pin 11, which is the TPS input on a TD/Carby TB so suspect it remains the same. Really I'd like to see a diagram before I just wire some voltage into there, or someone could check DC voltage between TCU Pin 11 and ground on a TB42E, with ignition on and move the throttle position?
    - TCU Pin 25? On the diagrams I have this runs out via a resistor to the Ignition coil. My guess was that this is an interrupt signal to cut spark during a gear-changes... does anyone know any better? Not sure if this is done or not here and if so I'll have to work out which would be the interrupt input on the VH ECU
    - Throttle Switch input. I think this one won't be too difficult, looking at the Gregorys and Haynes manuals its either a Closed or Full Open position signal (closed seems to make sense, though if anyone knows or can test definitively that'd be exceptionally handy). So i just need to find this signal to pull from the VH harness
    - Common ground. TCU Pin 15, this should be ok I have the corresponding VH harness location
    - RPM input from the engine. Does anyone know whether the GQ auto boxes have an RPM input from the engine, or a standalone sensor on the gearbox input shaft? 'Revolution Sensor' in the wiring diagrams is a little vague, and so I'm not sure where this is yet, though it may just be a little more research on my part. If there's another RPM signal from the engine apart from the 'Revolution Sensor' this is shown on my diagrams


    If anyone knows more about the above items and is willing to share or test i'd be super grateful. Alternatively, if you live in the North Perth area and have an Auto, TB42E-powered GQ and would be willing to let me check voltage on a couple of pins then I'm willing to pay a carton bounty if that helps sway you!

    Cheers guys

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    Patrol Freak jff45's Avatar
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    I thought the TB42 TCUs could run standalone i.e. not connected to ECU like the TB45E. The TB45E ECU dropped timing to 0 at shift changes but I don't know if the TB42E also did that.
    Maybe it's only the TB42S carby TCU that works by itself.

    I did a TD42T conversion from a TB45E auto. I retained the TB45E ECU only to continue using the TB45E TCU. It worked well but I've since swapped it out for a ZD30 TCU which also works with the TB45E ECU and has more suitable change shifting behaviour.

    My TCU gets its RPM signal from the dash tacho connection. As the TB45E ECU could no longer supply the tacho signal, I got a Dakota tacho signal converter to use the TD42 pickup to send the signal to the dash.
    As I retained the TB45E ECU, I didn't need to run the TPS signal directly to the TCU.
    John

    2001 GUII TI 4500 - Now converted to TD42T auto with Nomad valve body

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    Ah ok.. it does run without those inputs at the moment, and selects drive/reverse fine but I haven't been able to take it out for a run without the exhaust and see if it shifts correctly.

    RPM does work with the VH ECU and I have that wired into the Patrol tacho, so that's a good point I'll chase that and see if it has a TCU connection from there too. Timing makes sense, assume that'll be in the ignition wiring diagrams now that you mention it so I'll check there tonight

    Thanks for the reply

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