A little background:
84 Firebird, converted to LS1\460LE in 2006.
The car uses a Speartech ECM and harness.
A CableX box (Abbott Enterprises) turns the speedometer.
The speed signal wire used by the CableX box is coming from the Speartech ECM, not the VSS.

Recently, the speedometer has started "pegging". I can be sitting still and the speedometer will "peg" and the odometer will tick off the miles.

I'm seeing 10 DC volts on the speed signal wire coming from the ECM when the car is stationary.

I've used a product called AutoTap to monitor the ECM while driving and it is reporting what I believe to be the correct vehicle speed values.

The car is driven regularly and runs great. The Speartech ECM seems to be managing all other engine systems very well.

Am I measuring the speed signal coming from the ECM correctly?
Has anyone here ever encountered this situation?

Thank you for reading my question.

 

I sent an email to Abbott Enterprises and received a very quick response.

Here is a link that describes how to calibrate and field test the CableX box:
http://www.atrol.com/speedometer/cab...tion_chart.htm

 

My CableX box did not act as expected during the final step of the field test.

Abbott Enterprises asked me to send it to them so they can take a look at it.

I've been really impressed with their quick response to all my emails.

 

Abbott Enterprises has fixed my CableX box and it is on its way back home.

I've received outstanding customer service from them.