R33 GTR speed sensor problem?

[Snara]

Hi

I have problem with speed in my car. In low speed's sometimes car don't see the speed both on cluster and aftermarket ECU . I changed gearbox and speed sensor in the gearbox and still have the same problem. What else i should check?

[GTSBoy]

Change the speedo head.

Speed signal is +/- 1V sawtooth signal from sender to speedo head.  Speedo head electronics convert that to 0-5V squarewave for the ECU etc.  If there is no display or output at low speeds but it works at high speeds, then it's probably not a broken wire or loose connection.  it is some dodgy electronics.  You could take it to an instrument specialist.  You know, like we used to do back before the internet.

[CraigoGTR33]

Great knowledge GTSBoy.  I have a similar problem with my car although I dont have a seperate set of dials.  Perhaps  you can help?

I measured voltage at pin 53 of the ECU (speed signal in from cluster) with the car sat still and it read 4.8V,  when it was moving this value did not change.  According to the service manual it should read 5V (within 1V) and then have dropped to 2.5V at 40kmh.  Would you think this is a problem with the speedo head or the speed sensor?  Any tips to find out more? Are there some connectors in the dash that can cause hassle?  It looks like faulty connector or sensor to me but i could be wrong!

 

[GTSBoy]

The voltage transmitted from the speedo head to the ECU is a 0-5v square wave. It is PWM, so the pulses change width according to speed. Trying to measure that properly with a DMM is not the best idea. An oscilloscope is the best bet.

Anyway, if you have a constant 5V there it suggests that the speedo head is not doing what it is supposed to. It's unlikely to be the sensor. If you connect a mutlimeter on AC volts setting to the sensor and drive, you should see a 0.6v to 1v sort of reading.

And obviously any of the connectors in the circuits could be janky.

[CraigoGTR33]

Ok ill try that test and see what readings I am getting. 

Is there any information around the speedo head that you know of?  Ive got the white nismo cluster so it'd be a shame to take them out, better to fix them if possible.  I did have them out of the car a few years back and resoldered a few places which did the trick for a while but now the problem has returned!

 

[GTSBoy]

If it's the speedo, just pay an instrument shop to fix it.

[CraigoGTR33]

Ok to update the fix.. I took the instrument cluster out on the weekend and unscrewed the speedometer from the unit. On the back is a printed circuit board (PCB).  I saw a few videos on youtube for nissans around the mid to late 90s with problems similar to mine and they suggested simply resoldering all of the solder joints on that printed circuit board. 

I did exactly that and its worked so far!  No hicas fault lights and speed reading perfectly.  Power steering is working better and the engine seems to be running smoother but Im not sure if thats true or not! 

On the first test drive around the block the tacho also stopped working so i took that out and resoldered all that PCB as well. Hopefully I dont have to take them out again for a while. 

Thanks for your help GTS Boy - you were absolutely right that the clocks were at fault rather than the speed sensor.

[GTSBoy]

NP.

 Glad you could do it yourself. I've pretty much given up on suggesting that people break out a soldering iron!

[CraigoGTR33]

hahaha! yeah I must admit I wasnt expecting it to work, all the solder looked fine to me.  Goes to show that visual inspections dont really count when it comes to circuit boards... just resolder everything!

And now onto the next problem on the list.... ! #skylineownership