Everything I looked at for the 99 shows multiport injection? Gonna Wing it on GP. Most of the GM TB inj use dual injectors with a connector on top of each one. Pull them off and take a test light to the (I believe Pink or Red wire) and with key just in the on position you should have power on one wire to each one. If you do then the fuse is good. Next take the ground clip to the test light and connect it to the other wire on one of the injector connectors the other probe tip in the other wire and crank the engine, the light should flash meaning the computer is firing the injector. Most of these systems use lower pressure pumps and only spec at a modest 9-13 PSI. Any lower and it doesn't run. The test light is just a cheapy substitute for what is called a NOID LIGHT. You should be able to purchase one for your type system pretty cheap at the local parts house. Hope this helps.