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when you checked fuel pressure, did it hold for 4-5 minutes. then when you ran the engine did the pressure drop to specs.

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The bogging and hard starting you describe sounds more like weak ignition than low fuel pressure to me. The 4.3 liter GM V-6 has always been unusually hard on ignition components. This is especially so when the weather turns wet. Because of this tendency; many of those motors will run better and start easier if the spark plug gap is reduced from the originally recommended .060" to .045". If the plugs have over 10,000 miles on them, or show any sign of wear on the electrodes, or if the insulators are not consistently colored, I would install new plugs. I have found that this model is also far more sensitive to differences in brands of spark plug than most other motors. Champion is the one brand of plug that consistently runs well in the GMC 4.3 motor. I would recommend their # 4013 Truck Plug. The regular Champion # 13 Copper Plus is a more easily found option. And the # 3013 Platinum Power or # 7940 Double Platinum Power are premium quality options. The spark plug wires and distributor cap are two other parts which can cause this type of problem, if they are worn.

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The Fuel Pressure went to about 60 and did hold in the range for about 5 minutes.  When I started the engine it dropped to about 50 and held.  The next day when I went to start it again the pressure when I was cranking the engine only got up to 35 to 45 and would not start.  I could hear the fuel pump running between tries, but the pressure barely reached 50.


I changed the distributor cap and rotor, spark plug wires and plugs when I did the fuel filter.  The plugs are the Bosch Platinum+ that you don't gap.  The Jimmy has 128,000 miles on it.

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the fact that the fuel pressure did reach specs, and failed to reach specs another time tells me you most likely have a problem with a failing fuel pressure regulator. the spring diaphram may be weakening. if you don't know how to check this tell me. we won't talk about the injectors unless necessary.

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So the port on the fuel line that I tested the pressure on is not just testing the fuel pump?  I would appreciate knowing how to test the regulator.  Are they as prone to failure as the fuel pump? 

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The fact that the pressure was high at one time and than low at another, really sounds like the fuel pressure regulator (designed to REGULATE FUEL PRESSURE).

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