I have spark but will not fire. Can I dump some gasoline into what looks like a early style fuel injector with two ports, to see if the fuel pump has cratered.

anytime you disconnect the fuel rail, and if it has a bleeder/test port (looks like a tire Valve), Then it needs to be bled before fuel will reach the injectors. Also check Spark plug ignition as well make sure grounds have been returned properly.

pull the vacuum line from the regulator and turn the key on and see if gas drips or sprays out from the nipple on the regulator if so that's your problem the fuel is going threw the line into the intake port

needs air, fuel and spark. You have spark, make sure air filter is not clogged and the fuel pressure is up there; could also be water in fuel... dump fuel from filter in a glass bowl and take a look... replace filter and flush fuel system if water found. Injectors might need cleaning...

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Pull off one injector connector and use a test light or voltmeter to see if one wire has power with key on.
Power to the injectors is fed through the ignition switch, so with key on, you should have power there. The injector ground is inside the ECM. If you have power, you'll have to diagnose the circuit for why computer doesn't ground the circuit when it should.

It takes three things for a gas combustion engine to start and operate---air, fuel and fire---air is usually okay, fire sounds okay, according to you having "power", and the fact that it is intermittent---but still, check for spark---have someone wearing insulated gloves, unless they don't mind small pulses of 12VDC at about 50mA, which is not that bad, and have them hold a spark plug while still plugged into the wire very close to, but not touching, chassis ground. Or, put the spark plug while in the plug wire in a dark area, like down into the engine somewhere, and look for a spark. Either way, if your buddy feels a pulse or sees a spark, then you have fire. If not, it would likely be either the ignition module, usually in the distributor housing (under the rotor), or the ignition coil---you can obtain a schematic and check voltages if you wish---more often than not, in Chevys, it is the ignition module.

If you have fire, then it would be fuel related...depending on the delivery system (fuel pump, electrical or mechanical, or injection)---for an intermittent problem like this, it is likely electrical for fuel delivery, so not a carburetor or mechanical fuel pump---I would bet you have either tuned-port or throttle body injection---throttle body injection is one big port, like 1/2 carb, 1/2 fuel injector. If you have fuel rail injectors, then either they're all bad, or the ECM that controls them is dead (very unlikely)---my guess, if you have fire, is the fuel pump. However, I did have a Chevy Corsica with a bad injector (throttle body), which had the same symptoms.

There is no simple answer, there are to many variables. If you have access to a scan tool, pulling the codes should help. Without them its back to old school hunt and peck method. At this point we need to narrow down the problem. You need to test for spark.

1. Tag and disconnect the spark plug wires from the spark plugs.
   
2. Remove the spark plugs and install the spark plug wires to each spark plug.
   
3. Ground (do not hold spark plug) the spark plug; check if spark occurs while engine is being cranked.
   

Crank the engine for no more than 2 seconds at a time to prevent flooding the engine with gasoline.
If you have spark, You will want to make sure you have fuel injector pulse, along with fuel pressure. If you have spark ..simply spray some starting fluid in through the air filter and hold the gas pedal to the floor and crank it over while spraying. If it fires up, you know it is fuel related( fuel pump, regulator, or ECM if no injector pulse) . If you have no spark then look at ignition coil connection and trace through to the distributor( if equipped ). The crank shaft sensor has a tendency to fail on these as well. This should give you a few things to test and check to start you on your way to narrowing it down. If you have no spark then look at ignition coil connection for power and trace through to the distributor( if equipped ). If it is DIS( no distributor). It may be the Crank sensor or the ECU. The crank shaft sensor has a tendency to fail on these as well.
The ECU uses the signal sent from the Crank sensor to trigger the spark and fuel injectors. ( make certain you have checked all fuses)

THE FUEL IS PRESSURIZED BY A FUEL PUMP INSIDE THE FUEL TANK, THE INJECTORS ARE OPENED AND CLOSED ELECTRICALLY BY THE FUEL INJECTION COMPUTER KNOWN AS THE ECM, THE COMPTER/ECM RECIEVES INFORMATION ON WHEN TO INJECT FUEL AND FIRE THE SPARK PLUGS FROM THE CRANKSHAFT AND CAMSHAFT POSITION SENSORS, HOPE THIS HELPS

if you've gotta dump more gas in it than it should be getting, it may have a large vacuum leak

First, never use starting fluid on a gasoline engine. Check for dirty air filter, then check for Mass air flow sensor (Fault code) . This sensor controls fuel mapping, bad signal here will cause over fueling (black smoke) also called loading up (rich). Stopped up Air filter will affect Mass air flow. Perform OBD II test to prevent buying unneeded parts. Also delete stored codes.

check the spark plugs, and the fuel pump checked. never try additives to clean the fuel injector with ur gasoline, it never works and in fact screws up the system.

the spark plugs change would solve ur problem.

good luck.