I have been noticing a difference in the RPM my tach is showing when I'm cruising on the Hwy. In the cool of the morning...about 5am...heading to work, I am seeing 2000rpm at approx 100Km/h. But in the heat of the day, late afternoon heading home, I am seeing 1850-1900 going the same speed.
I never saw any fluctuations before when I was running the magnetic tach signal pick up on the harmonic balancer, and this very same Isspro tach.
Only thing I can think of is maybe the CPS is going bad, or there is a weak link in the wiring? And the heat of the day is causing a deterioration of the CPS signal?
Thoughts, ideas?