1988 Chevy Truck timing not right

When checking timing per emission sticker timing will not go to base timing?Base timing should be zero but cant check?I've had some running issues and codes. Replacement of these parts were nessary. Coolant temp sensor for computer, egr diaphram leaking, tstat sticking over heating, catalytic converter blockage. Truck runs and idles but after a short distance dies, [like if flooding condition]. Turns right back on and will not repeat problem until truck cools. Code 42 pops up which is normal because truck dies cutting off signal to computer no help. Thanks for the help.