Have you replaced the fuel filter? Have you checked the fuel pressure and flow? Is there a check engine light on?
no no and yes check engine light is on
carburetor is making a buzzing sound too
It should TB injection, replace the fuel filter and test the pressure and flow and get the codes, this has OBD 1 so go to: http://www.youtube.com/watch?v=UIKdbTFvyUU
Check what tennisshoes has specified. Is it electrical or mechanical buzzing. The fuel pressure regulator is built into the TBI, it would make a mechanical sound if plugged. Most of the time you can remove the TBI and clean it out. If the gaskets don't tear and look good I have re-used them (just monitor for leaks once you get it running again). 1990 shouldn't have the quick dis-connect fuel lines if your lines are rusty spray them with a penatrant and use line wrenches so that you don't round them off. Electrical buzzing? I doubt it would be the injectors, when they go they either stop spraying or spray continuosly. The Idle Air Control Valve is on the TBI but I doubt it would cause this, usually will not idle or will surge if this is damaged. I'm leaning towards the regulator. Clean it then change the fuel filter (on the driverside framerail under the cab, use line wrenches and lube on these fittings also, don't want to twist the end of a line off).
I have a 1978 that does the same thing. Going to replace the fuel filter and go from there. Someone also suggested to me that the fuel pump might be going bad as I can't enough power at high speeds.
@ SanDane Yes the mechanical fuel pump is a good place to start. The rubber supply line from the steel line on the frame to the suction side of the pump should also be checked. The older lines can swell on the inside and choke off fuel flow.
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