Hi, welcome to Just Answer.
Sounds like you either have a faulty Pickup Coil inside the distributor, an air gap adjustment, or a faulty Distributor. Be sure you have 12 volts to the ignition coil as well...we don't want to overlook a bad ignition switch or power supply problem. below are the procedures on the Pickup Coil.
SINGLE PICKUP DISTRIBUTOR
See Figures 1, 2 and 3
Raise the hood or engine compartment lid.
Remove the distributor cap.
Align one reluctor tooth with the pole piece pickup coil. If the truck is equipped with an automatic transmission, bump the starter motor using the key. If it is equipped with a manual transmission, place the truck in 3rd or 4th gear and roll the truck until the tooth is aligned.
Fig. 1: Air gap adjustment on a single pickup distributor
Fig. 2: Single pickup distributor-1972-86 V8 engines
Fig. 3: Single pickup distributor with Electronic Spark Advance (ESA)-V8 engines
Loosen the pickup adjusting screw. On 1972-76 models, insert a 0.008 in. (0.20mm) feeler gauge. On 1977 and later models, insert a 0.006 in. (0.15mm), feeler gauge. The gauge should not fit into the gap. Do not try to force it in.
Apply vacuum to the vacuum unit and crank the engine. The pickup pole should not hit the reluctor teeth. If it does hit, readjust the gap. If it only hits on one side, the distributor shaft is probably bent and must be replaced.
Install the distributor cap.
DUAL PICKUP DISTRIBUTOR
See Figures 4 and 5
In the dual pickup distributor, the start pickup is identified by a two-prong male connector. The run pickup is identified by a male and a female plug.
Fig. 4: Air gap adjustment on a dual pickup distributor
To adjust the air gap on the start pickup, follow the previous procedure for single pickup distributors.
Align one reluctor tooth with the pickup coil tooth.
Loosen the pickup coil hold-down screw.
Insert a non-magnetic feeler gauge 0.012 in. (0.4mm) between the reluctor tooth and the pickup coil tooth.
Adjust the air gap so that contact is made between the reluctor tooth, feeler gauge and pickup coil tooth.
Tighten the hold-down screw.
Fig. 5: Dual pickup distributor-1981-86 6-cylinder engines