Erratic Wheel Speed Signal

Hi guys,

I am setting up ground speed launch control on my VW Beetle with a Haltech Elite 1500. I have a wheel speed sensor on my front left wheel and I have a problem with the speed plot being erratic. The sensor I have is a Hall Effect unit which is connected to the standard Beetle speedo cable, and gives 6 pulses per wheel revolution. I have the sensor wired to Ignition +12V, the output to SPI 3 and the ground to chassis ground. In the Haltech software I have the Falling Edge selected, sensor type is Hall Effect and Pull up is Enabled. I'm not sure if using chassis ground as opposed to Haltech sensor ground is a problem or would cause these issues. Attached is my datalog of front wheel speed to show the issue i'm having.

Since you are using a speedo cable, are you sure the triggers targets for the sensor are evenly spaced (and that the cable isn't binding and thus speeding up and slowing down? Some systems offer a "sample teeth" option that average 2 or more triggers to keep the speed consistent. I often use a sample teeth of 3 to overcome trigger spacing (bolts), that are located in groups of two around the hub (Tripod CV joints).

Thats a great idea thanks David. It looks like Haltech have just released filtering for Vehicle speed sensors in their latest firmware. Ill give this a go.