(1991 Sonoma 2.8L) I can watch the injectors run out of gas as the pressure drops, but how can I tell what is causing this? So far I have checked voltage at the pump (good), replaced the filter (new), I have had the tank apart and found bad connectors (fixed those) and although It runs better, it still stalls. Is it the pump or the regulator? P.S. the trunk ran great, but has been sitting for about 6 months and the gas is new.

It's very common for injectors to get clogged. Sometimes a good injection cleaner you put in your fuel tank works and sometimes a professional cleaning works but then again sometimes they don't work at all. Replacement injectors always work, if the fuel pressure was to high all the injectors would flood but check anyway. I hope this helps, Take care

Too much gas. Maybe the fuel pressure regulator has failed. Pull off the vacuum hose to the regulator-if any evidence of gas in the vacuum line, regulator is bad-diaphragm has ruptured and letting in extra gas to engine through the vacuum line.
If that is good, no gas in vacuum line, have the fuel pressure checked. Still possible the regulator is not right.
Watch the pattern of gas out the bottom of injectors while the engine is cranked. Should see a fine mist cone pattern spraying out from the injectors. If it is just dripping, injectors may be clogged.

You might want to check the wires that go to the 02 sensor it sounds like when the tune up was done the wires may of become dis-connected. Unless of course the tune up was done to correct the problem. In that case first check for gas leak under car and around gas tank, if OK then, next ( I take it there's no check engine light on) borrow a fuel pressure tester from Auto Zone and test the fuel pressure After you've hooked up the tester run the engine a few minutes then shut it off and watch the gauge it it slowly drops you more then likely have a leaking fuel injector.If in fact this is the case, before you replace the injector run the fuel down to 1/4 tank and add a good fuel injector cleaner to the gas and run until close to empty. Put fuel in tank and drive at least 50 miles to allow fuel system to clean out. If still the same then the injector is bad. Note; You could also have a bad 02 sensor but that should set the check engine light.

COULD BE FUEL PUMP.CHECK FUEL PRESSURE SHOULD BE 40 - 47 PSI. WITH NEW FUEL FILTER. IF FUEL PRESSURE OKAY.YOUR SPARK PLUGS COULD BE FOULING OUT BY LEAKING FUEL INJECTORS.CLEAN FUEL INJECTORS BY ADDING A CAN OF SEAFOAM TO 3/4 TO FULL TANK OF GAS.WHEN YOU HOOK UP FUEL PRESSURE TESTER WITH IGNITION SWITCH ON ENGINE OFF FUEL PRESSURE SHOULD READ 40 PSI. TURN OFF IGNITION SWITCH IF FUEL PRESSURE DROPS FAST YOUR FUEL PUMP CHECK VALVE BAD.IF FUEL PRESSURE DROPS SLOWLY IN TEN MINUTES TIME FUEL INJECTORS IS LEAKING A NEED CLEANING.INJECTORS SPRAYING TIP CLOGGED WITH CARBON BUILD UP CAUSING THEM TO LEAK DOWN WHEN ENGINE OFF.

Have you checked the injectors and wiring. sounds like bad injector or wiring not sending pulse from pc.

yes it is possible to have a failed injector. test pulse and then remove the rail, leave the injectors hooked up electrically and have someone turn the key on (prepare for fuel spray by disconnecting the ignition and covering the area with a protective cover to also prevent the risk of fires), and watch for the patern. you can also isolate the problem easier by when it is running, disconnecting the harness at the injector or plug wire and notice the engine change. the one that doesnt change, is your problematic cylinder. then test accordingly.

Check the fuel pressure at the shredder valve, you should have 62 to 65 PSI when the fuel system is primed. (engine not running) With the engine started and running the pressure should drop by 5 PSI, anything less then 62 PSI in your fuel system when trying to start the engine will cause a no start. Note; that try to start a the engine by pouring gas through the throttle body may cause an internal fire in the intake ports and will cause the fuel injectors to melt creating a more expensive problem. As for the fuel pump in the gas tank, it''s held on by and snap ring which you can remove with a simple screw driver. Good luck and keep me posted, and don't for get to replace the wire harness from the frame to the gas tank. It's a $12.00 investment that's worth more then it's cost.

Check the fuel pressure at the Shredder Valve, You should have 60PSI to 65PSI upon start and should drop about 5PSI when running. If your fuel pressure is good then it may be a bad injector system. The fuel injector spider system that the vortec has are know to go bad, from the fuel pressure regulator to the puppet fuel valves. Change the fuel filter first if it has not been changed yet and have the fuel pressure check. Good luck and keep me posed. Note: it's been know that spraying ether to start the vortec with the spider injector system has got the puppet valves to catch fire and melt the ends of the puppet valve leading to the replacement to the whole system. Good luck and keep me posted, be glad to help.

Check the vacum line to your fuel pressure regulator. Keep it simple and start with that, dubble check your firing order again. Good luck.

Have you checked for fuel in the fuel rail? If so have you checked the injectors. If the problem is located in the injectors then there are two possible problems:
1...All of your injectors are clogged. Highly unlikely but possible.
2...Your computer is not sending a injector cycle command to the injector. This could be caused by a faulty cam position sensor or a faulty computer.