Read speed via OBD-II without PCM [ISB swap]

[cray54]

I'm helping a cousin to setup some digital gauges that normally connect to an ODB-II port. His swap is a 24v ISB from a 98 Dodge into a 79 Ford F250. The PCM was not swapped. I understand OBD-II codes can be read directly from the ECM.



Was speed information collected by the ECM or the PCM? What would be the best way to collect speed information to send through the ODB-II port to the digital gauges / data acquisition setup?



Thanks,

Chris

 

[AlaskanCummins]

Speed is taken from a tone ring in the rear end of the donor truck. A sensor mounted on the pumpkin sent a signal to the ABS module that was mounted on the drivers side firewall area. That info is then shared with the PCM and then to original gauge cluster. Basically, Dodge uses a "can bus" system for 6 modules to all communicate with each other.

So, in a nutshell, it's not going to work. I ended up using a speed unit called "cable X" with a rigged up speed sensor mounted on the tail cone of the t-case and a speed ring welded to the drive shaft. I now use a Dakota Digital GPS unit to communicate with the cable X and cruise module.

Good luck.

 

[Bob4x4]

The can bus was not used till 06. The rear Wheel Speed Sensor (WSS) is mounted in the rear differential housing Rear Wheel Speed Sensor Location The WSS consists of a magnet surrounded by windings from a single strand of wire. The sensor sends a small AC signal to the CAB. This signal is generated by magnetic induction. The magnetic induction is created when a toothed sensor ring (exciter ring or tone wheel) passes the stationary magnetic WSS. Cab=controller ant-lock Brake.
The PCM uses a speed pulse input received from the Controller Anti-lock Brake (CAB) and internal programming to decide what vehicle speed and distance messages are required. The PCM then sends the proper messages to the instrument cluster circuitry on the CCD data bus. The CAB uses an input from the rear wheel speed sensor and internal programming, which includes a programmable pinion factor to compensate for different axle gear ratios and tire sizes, to determine what speed pulse output is required. The CAB then sends the proper speed pulse to the PCM on a hard-wired circuit.