2 replies to this topic

[schmoo]

I'm in the midst of replacing the stock instrument cluster in my MSM with an AIM MXL. The MXL is connected to a Hydra ECU, from which it can normally pull speed, water temp, air intake temp, rpm etc.

Having taken my first test run with the new set-up tonight, I noticed that I'm not getting a speed read-out on the MXL. I therefore connected my laptop to the Hydra to see if it was outputting speed. It wasn't.

I checked the wiring diagram and it appears that removal the stock cluster appears to have broken the circuit that sends the speed signal to the ECU.

It appears that the signal from the Vehicle Speed Sensor comes to the IC via an Orange and a Yellow wire at 2M and 1M on the IC harnesses. ECU-bound signals leave the IC on a number of wires.

While my MXL can get speed via GPS, I like have a wheel speed sensor, plus the wheel speed allows the Hydra to output a gear value to data logs as well. As such, I'm wondering if:

1) bridging the orange and/or yellow wires with other wires will re-establish the link between the VSS sensor and the ECU;
2) which wires need to be bridged; and
3) is it as simple as a crimp/solder, or do I need to put a resistor in there, too?

Thanks everyone!

[schmoo]

Just a quick update in case anyone is interested.

Joining 2M to 2L on at the IC and grounding 1M appears to have bridged the signal, but the signal appears to be different, as if a flow restriction has been removed. The result is that the ECU is under the impression that we're moving much faster than we are.

I'm hoping that adjusting the calibration value in the ECU will allow me to bring the value back into line. I'll be trying this tonight.

[schmoo]

Success!!!!

My initial VSS calibration value in my Hydra Nemesis was 253. Now it's 113 and speed is accurate.

What I've observed: the VSS signal is extremely responsive now. The speed display moves very rapidly up and down and can oscillate between two whole numbers (e.g., 64 and 65).

My hypothesis: the electronics in the IC smooth the raw signal to produce something that is easily processed by a speedo needle. This smoothed signal, probably one with pulses at a lower frequency, is what would normally serve as the VSS. Now, I have the raw signal with more pulses per shaft rotation, thus requiring a reduction in the Hydra calibration values.

Hope that's useful to someone in the future.