A '91 189 (3.1L) runs with the fuel pump unplugged, but won't run with the pump connected? As you well know, that engine is a multi-port injected type, normally requiring fuel pressure and injector pulses to administer fuel.
Given the symptoms, I'd suspect a significant fuel leak in the system, either via a stuck/blown FPR or static injectors. Raising the rear of the vehicle may provide sufficient gravity flow to allow fuel to feed to either the static service injectors or backward through the FPR, allowing the engine to run, albeit richly. Connecting the pump would likely provide far too much fuel to start and run the engine.
Raise the rear of the vehicle, stand on one foot, close one eye, or do whatever you have to do to get the engine running. While running, disconnect the injector electrical connectors one at a time, and keep them disconnected. See if it still runs. While the injectors are unplugged, test each injector solenoid coil resistance. If any of them are below 9.8 ohms, do not reconnect those. If any are shorted to ground, do not reconnect those.
If the engine stops while you are unplugging injectors, the last one unplugged may be shorted. Reconnect the fuel pump to establish injector pressure, and try it again. If the engine does run on the remaining good injectors with the fuel pump running, replace the faulty injectors.
If the engine will still not run with the fuel pump running, and all the injectors check good, there may be a major fuel leak in the FPR and/or fuel return line. To test this theory, you can pinch the fuel return line closed in the engine compartment while the engine is running and judge by the result.