83 or 84 380 have 2 pressure regulators. The system fuel pressure regulator is in the fuel dist. Then there is the control pressure regulator bolted to the front of the intake manifold. Some places it is called a warm up regulator. Its purpose is to reduce the control pressure when the engine is cold which makes it run rich and increase the control pressure when the engine is warm to lean it down. A common problem is a restriction in the inlet to the control pressure regulator or no power to the electrical connector. It takes a special fuel pressure guage to check the operation of this control pressure regulator. Now I'm not sure which pressure regulator you are refering to but if you will explain how the runs both cold and warm maybe I can add more to the subject.

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84 500 SEL (307,xxx miles)