Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Disconnect the CMP sensor.2. If the engine runs good at that point, remove the distributor rotor.3. Check the top of the vane cup for a "6" or an "8". This is not the "8" or "6" that the distributor is aligned to during installation.4. If a "6" is present, the wrong distributor, one for a 6 cylinder engine has been installed in this 8 cylinder engine
if the distributor is correct then only thing there is valve adjustment to tight you said 3/4 is to much you should do 1/2 the most and see what happens to much will increase pressure on the intake and drop vacuum. make sure you have a vacuum gage attach so you can read vacuum as you doing it.
do not remove the timing cover yet lest confirm with the distributor first put the engine to top dead center on compression stroke then remove the distribuitor cap check the position of the rotor is it line up to #1 cylinder?
and if it is then get your self a vacuum gage let the engine worm up read vacuum is it less then 14 inches ?