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...

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.

Hi Paul I hope you may be able to help me i've got a problem with my tacho/rpm output from my apexi power fc, firstly i was convinced it was the old dry solder joint issue with the rb25 tacho but having now changed 4 sets of tachos and also realising my avcr is also giving the same erratic reading as the tacho it leads to the pin 7 rpm output of which the avcr is also soldered. So far all the testing is done with the ignition on only. My clocks and the avcr don't move at all with the ignition on. First thing I did was disconnect my avcr but no joy there then also the vems unit and still nothing. Then the dash clocks themselves in case a ground on there was an issue.. I currently have 0.68v on the rpm wire with ignition on only, which jumps up or down every 6/7 seconds you can set your clock by it what i'm not sure of is this causing the problem or is it normal, i don't know anyone else with a power fc on a skyline that could test pin7 voltage and give me something to work with. I have been up and down all the rest of the pins on the ecu. All the grounds are fine and the positive feeds, I found that the consult output wire was sending out a similar jump but this is likely as this would be the output for diagnostic. The other one which only showed a small milli voltage change just before the tacho jumped is pin 36 air intake temperature signal?.. There must be some signal going out from the ecu every 6/7 secs and basically it doesn't like the return signal and it maybe this that's causing the problem but I have no idea what this could be. Also need to point out the car runs fine and the hand commander shows the rpm spot on with nice steady readings even when the standard tacho is going crazy so i ruled out the cas as i know the signals come from this to enable the ecu to create the rpm output.. I did check my partners car and my standard skyline and both of those have a constant steady voltage with the ignition on.. I have had a little help from someone called jarrod on the SAU forum who had a similar problem but he identified is as been the standard boost solenoid wire and when he cut it his problem was then solved. Therefore any bad signal into the ecu could be causing this? I hope you may be able to help mark

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..

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.