R34 Speedo Issue (send help)

[R34GTTBoi]

Howdy fellas. I have an issue:

TL;DR - 34 GT - Turbo & manual converted (Speedo was working) - Installed 34 GTT motor and loom - Replace ECU & Tuned - Now no speedo. Checked wires from sender & reversed. Checked fuses in drivers footwell (trip metre fuse in drivers footwell). Only other change was the *Anti Skid Control* box has been removed.

Send help please: Unsure of where to go next.

Long story - 
Bought car, already manual converted. Replaced motor with GTT motor and motor loom (loom all the way to ECU plug). The plugs didn’t match the Anti skid control so I’ve ordered one from a GTT but I don’t think that will fix it. I investigated the speed sender and signal seems good. Unsure of where to go next.

Update** Now suspect maybe gearbox loom or earth isn’t quite right? Maybe it came look/dislodged in removing the motor?

I have trawled the hell out of Skyline Owners and SAU before someone links an article there.

[GTSBoy]

I have to plead a little ignorance of what should have been on your car in its original state.....but it is my gut feeling that the NA auto R34s had the speed sender on the diff nose, not the gearbox.  I might be wrong, but it is something to consider.

The RB25DET's manual gearbox speedo sender creates a +/- 1V signal (essentially an AC voltage), the frequency of which varies with speed.  The speedo head reads this and converts it to the 0-5V square wave PWM signal that gets put out onto the speed signal bus (which goes to the ECU/TCU, the ABS/TCS & HICAS CU).  All of those CUs are only receivers on the speed signal bus.  None of them create the speed signal.  Any one of them can be missing completely and the speed signal should still be available.  So long as the speedo head is still doing its job.

The only wires you have to worry about are the 2 wires that run from the speed sender to the speedo.  There is no power (car battery 12V, no earth) involved.  Just the connection between sender and speedo.  of course, the speedo is separately powered off the dash.

It is just possible that the diff mounted speed senders create a different type/quality signal from the gearbox ones and that might explain the speedo head's inability to read it.

There are other alternatives.  The speed signal might be good, the speedo might be good (in terms of receiving the original speed signal and transmitting the square wave version out on the bus.....but the head might have simply died as a coincidence.  Unlikely -- coincidences are to be suspected.  But possible.  A worthwhile test will be to put a scan tool onto the car and take it for a drive.  See if the speed signal is visible from the ECU.

[R34GTTBoi]

As stated in original, speed was working with manual conversion before hand. Only since removing old motor and putting in GTT motor has issue occurred.
Aftermarket ECU is installed now as well so diags won't help.

Edited November 30, 2018 by R34GTTBoi

[GTSBoy]

Scan tools can interrogate all other CUs in the car, including HICAS and ABS/TCS.  They should be able to see the speed signal (if it's there) even without the original ECU.

[NZ-GTT]

I have a factory manual GTT. A while ago I tested an ecu from a Stagea rb25det neo auto in my car and everything worked except the speedo so it could well be an ECU issue.

[R34GTTBoi]

Ended up being the wire to the dash - ran one manually and we were good to go.

[[email protected]]

On 13/03/2019 at 8:34 AM, R34GTTBoi said:

Ended up being the wire to the dash - ran one manually and we were good to go.

Im having same issue after replacing motor. No rpm, speedo and faulty temp. Where did you run a wire to and from? Think this might solve one of my issues. Cheers