Where is the ECM on the truck on 1991 GMC 1500 Pickup

Fuel injections are getting fuel but, the truck still will not stay started.
I also want to know where the ECM is located on the truck?

The ECM is located behind the dash on the passenger side, you will need a wiring diagram to proceed with testing. If you have fuel injection it means the ECM is receiving power, seeing crankshaft rotation and processing this information to trigger the injectors. Do you have ignition or does the truck loose ignition once the ignition key is released from the start position? If the engine starts and runs it must be mechanically sound.
2 more answers
where is the ECM on a 1999 dodge ram 3500 5.9 L diesel?
electronic control module is the computer behind glove box.