[mcramsay]

I have had major trouble getting my stack speedo to work correctly, and it's the last issue on my car to sort out, iva is booked for 19th of October so I have some time to sort it

Bit of background info, stack speedo with a 3 wire Hall effect sensor mounted on the drivers side inner cv joint picking up a bolt head glued on the joint.

I have had issues where the speedo has been counting pulses that don't exist( when calibrating the speedo you put it into calibration mode and you can watch it counting pulses. So after lots of testing and even sending the unit back for testing at the factory I have found the issue. All the wiring for the car runs in one loom to the rear, when in calibration mode with the wheels not spinning the Lp facet fuel pump is inducing a voltage causing the speedo to read haywire. With an oscilloscope on the trigger wire I can see a very noisy signal along with pulsing AC waves which will also affect the reading. I bypassed the signal wire for the speedo to move it away from the fuel pump wiring, this worked temporarily however I think I may be getting some AC induced into the 12v supply to the sensor which is then traveling back up the signal wire. All a bit complicated I know... Even more weird is that it takes around 5 mins of the fuel pump running to start affecting the speedo. If I unplug the pump the speedo instantly behaves normally.

So the easy answer is to move the fuel pump wiring away from the speedo wiring but I will have to take half the car apart to do so.

Is there anything I can put in line on the supply and signal wires on the speedo to remove any induced noise?