Fuel pump Issues

If it is not cranking, that is a starter system problem.

You should only have twelve volts to the fuel pump for one second when you turn on the ignition switch, then it should go to zero volts. The twelve volts should come back during cranking.

If you find twelve volts for that first one second, and during cranking, but you do not hear the pump running, if you have a steel gas tank and it is rusty, ground a test light to a paint and rust-free point on the body or frame, not on the gas tank, then poke the probe on a rust-free point on the gas tank. Have a helper crank the engine. If the test light turns on, even if it is just dim, there is a bad ground on the tank. To solve that, drill a small hole through the flange, outside the welded seam, where the top and bottom halves are welded together. Run a self-tapping screw in that hole. Do the same thing on the frame or body. Sand both points clean, then connect a new wire between those two screws.

Dandy. The smaller GM trucks that had steel gas tanks had a lot of trouble with losing the ground for the fuel pump when the tanks got rusty. The ground was made through the tank straps.

Your fuel pump relay is working correctly. If you do not have fuel pressure, it sounds like the pump has failed again. This used to be a common and frustrating problem with Chrysler products. People would replace the pump with an aftermarket one that failed within a few weeks. They would get it replaced under warranty, and that one would fail the same way. Out of frustration they would try two or three different brands, all with the same result. Finally they would buy one from the Chrysler dealer and have no more problems, so of course they assumed it was the quality of the aftermarket pumps that was the problem.

In fact, what was happening was there was debris in the gas that was plugging the impellers in the pumps. This was most common when we started using gas with ethanol. Mold builds up that feeds on that alcohol. Chrysler fuel pumps are extremely quiet because they have such tight clearances between the impellers and pump bodies, but that made them prone to locking up. Each time the pump was replaced, some of that gunk got collected in the old one and was removed. It was just a coincidence that by the time the dealer's pump was installed, the debris in the tank was gone.

In fact, the supplier that builds fuel pumps for Chrysler also sells them to a lot of the auto parts store chains. NAPA is one in particular that I remember. Their Chrysler pumps come from the same place Chrysler gets them from. We finally learned that the proper repair was to have the gas tank steam-cleaned at a radiator repair shop, then install the new pump.

You also have a pickup screen on the housing the fuel pump sits in. If you are just replacing the pump and motor but not the entire housing assembly, that pickup screen is likely plugged. With engines that have the fuel pressure regulator on the fuel rail on the engine, a common symptom to a plugged pickup screen is the engine will stall when the largest volume of fuel is being pumped, which is during coasting. A clue to identifying this is to disconnect the vacuum hose at the fuel pressure regulator and plug it. Fuel pressure will be too high and you will have black smoke from the tail pipe, but the stalling will not occur.