I have a 93 blazer with a 95 4.3L vortec. It cranks but doesn't start. I have the obd 1 connector. I can't find a code reader that works so I jumped the a and b terminals and got a code 34. I tested the map sensor and have good voltage to the connector 5.0 volts at terminal c and a. When I plug it back in I only get about 2 volts when back probing terminals c and b. would this cause a no start problem?

I have replaced coil, pick up coil, icm, temperature sensor, new plugs and wires, rotor and cap.