I know that MSD warns about where you run the cable that runs from the distributor to the control box. If it is near a spark plug wire or some other source of RF interferance you maybe getting false signals from the distributor pickup. They (MSD) tell you to run the cable where it will be shielded by metal objects. I ran mine over the A/C unit and as far away from the wiring harness and spark plug/coil wires as I could.