Faulty Tacho Signal From Power Fc. Electrics Guru Needed..

[mark68]

The problem is i have a very erratic rev counter which I know your going to say is a common problem with the rb25 clocks and dry solder joints, but having changed the clocks now 4 times now i have started to have my doubts..

To confirm this i have also noticed my apexi AVCR which is also taking its rpm signal off the same pin/wire as the clocks (No7) is mirroring the dash tacho..

Therfore the signal out is erattic, i have a Power Fc rather than standard ecu. I undertsand the signals come from the cas into the ecu and the ecu converts these signals into the tach output (pin7), i am wondering if the cas is possibly faulty or the wiring from the cas to the ecu is an issue.

[mark68]

Further update,

The rpm output pin 7 has approx 0.68v output then every 6 or 7 secs it jumps either up or down. You can set your clock by it ... This is with the ignition on but not running. I've checked my other r33 and this is a constant voltage so hear lies the problem..

I cannot find what is causing it though all the grounds to the ecu are fine and have continuity and I cannot identify any other pin on the ecu that is also changing voltage or resistance when the jump happens.

Does the apexi ecu send a signal either out or receive one in every 6 or 7 secs for any particular thing as this might narrow my problem down a bit..

[BH_SLO32]

There is a power feed to pin 7 (from the dash cluster presumably) and the ECU simply earths the signal to create the pulse. It is opposite to the old school feed from the coil (eg RB30).

Cheers

Further update,

The rpm output pin 7 has approx 0.68v output then every 6 or 7 secs it jumps either up or down. You can set your clock by it ... This is with the ignition on but not running. I've checked my other r33 and this is a constant voltage so hear lies the problem..

I cannot find what is causing it though all the grounds to the ecu are fine and have continuity and I cannot identify any other pin on the ecu that is also changing voltage or resistance when the jump happens.

Does the apexi ecu send a signal either out or receive one in every 6 or 7 secs for any particular thing as this might narrow my problem down a bit..

[mark68]

i thought the rpm feed was outward from the ecu to the dash clocks not coming in ?, and it was generated by the ecu, even with the dash cluster unplugged there is still the voltage i mentioned above on the rpm wire.

There is a power feed to pin 7 (from the dash cluster presumably) and the ECU simply earths the signal to create the pulse. It is opposite to the old school feed from the coil (eg RB30).

Cheers

[BH_SLO32]

If you unplug the ECU and check pin 7 on the loom you should see around 5-10V with the IGN on.

I am not sure on the wiring between the dash and the ECU but the ECU is fed power to pin 7. The ECU will then earth pin 7 to create a pulse (eg 5V-0V-5V-0V etc) at the required frequency.

i thought the rpm feed was outward from the ecu to the dash clocks not coming in ?, and it was generated by the ecu, even with the dash cluster unplugged there is still the voltage i mentioned above on the rpm wire.

[mark68]

thanks for that, I am glad to report that after disconnecting my avcr and doing a road test the tacho worked fine, i'm not convinced it was this causing the issue as i've put it all back together and so far they are still working ok. There is obvioulsy a bad contact somewhere in the wireing..

I have learnt alot about the signal and how it works though, it is a constant voltage feed whilst the car is running so next time if it happens i will know what to montior and what it should read...

If you unplug the ECU and check pin 7 on the loom you should see around 5-10V with the IGN on.

I am not sure on the wiring between the dash and the ECU but the ECU is fed power to pin 7. The ECU will then earth pin 7 to create a pulse (eg 5V-0V-5V-0V etc) at the required frequency.

[1NOORTIEONE]

G’day all , while on this topic does anybody know what colour & which wire is the tachometer outlet on the apexi fc30 commander. Any knowledge would be greatly appreciated.