Re: 97 LT1 help needed
Tach is driven off the PCM, based on the cam position signals from the Opti. If the high resolution pulse patter is going erratic, might cause the tach to jump around. The high res pulse signal won't set a code unless it totally disappears for 10 crank revolutions.
Might be worth checking the harness connector at the Opti, for corrosion or a bent pin.
I'd try another scanner. There are $25 cheapies that will pull the codes. If that shows no connection, the wiring for the ALDL connector needs to be checked. Did you verify you have 12V on pin 16?
94 Formula A3+1: 381ci all-forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / Comp Cams custom solid roller / TH400+GearVendors OD/4.11's / Strange 12-bolt / 300-shot N2O / Spohn Suspension / 6-pt roll bar with integrated SFC's / full AutoMeter instrumentation / MoTeC M48 Pro engine management system / a few other odds 'n ends. 800HP/800LB-FT at the flywheel.