1989 Dodge Van fuel pump

When you turn on the ignition switch, the fuel pump and automatic shutdown relays turn on for one second, then turn off until the engine is rotating, ... Cranking or running. If those relays are staying on when the engine isn't rotating, either someone hot-wired them which bypassed the safety circuit, or the crankshaft position sensor is sending a "noisy" signal that the Engine Computer is interpreting as a signal and is keeping those relays on.

The way the circuit is supposed to work is if the fuel line is ruptured in a crash, the engine can't run with no fuel pressure, so it stalls. Pulses stop coming from the crankshaft position sensor so the Engine Computer turns off the relays so fuel won't be pumped onto the ground and create a fire hazard.

The crankshaft position sensor is in the transmission bell housing, right behind the right cylinder head. It's just a few inches from the distributor.

I can never remember which vehicles this applies to, but some run the fuel pump on the automatic shutdown relay, and some have their own fuel pump relay. When there's two separate relays, the coils are wired in parallel so they both turn on at the same time and are controlled by the same terminal on the Engine Computer.

My guess is someone hot-wired the fuel pump relay because they thought the pump was supposed to run anytime the ignition switch is on. That's a common misconception. The Engine Computer turns those relays on when it sees pulses from the crankshaft position sensor and the camshaft position sensor.

The easiest way to see if the circuit is working is to measure the voltage on the positive terminal on the ignition coil, either smaller terminal on the back of the alternator, or the feed wire, (usually dark green / orange), on any injector. You should see 12 volts for one second after turning on the ignition switch, then again during engine rotation, (cranking or running). Many digital voltmeters don't respond fast enough to catch that one-second blip. A test light works better for that test.

I checked a different source today and they indeed do not show a crank sensor, but they do list a carburetor for your engine, which is not correct.

I don't have a wiring diagram in front of me but I suspect the resistance readings you found are normal. The "ASD input" comes from the relay contact that gets energized when the relay turns on. The computer turns the relay on, and that terminal tells it it was successful. Also tied to that circuit is the ignition coil, injectors, alternator field, and oxygen sensor heaters. The fuel pump relay's coil, or the fuel pump, (when a separate fuel pump relay isn't used), will be on that circuit too. That coil, and all of the other things on that circuit could have a combined resistance of around 32 ohms, so your ohm meter would read 32 ohms between terminal 10 and any ground wires.

Another way of looking at it is there's 32 ohms of resistance to ground on that circuit. Using Ohm' Law to calculate current flow, (current = volts / resistance), 12 volts divided by 32 ohms equals.375 amps. That's not much. That circuit is usually protected with a 15 or 20 amp fuse on newer vehicles, or a rather substantial fuse link wire on older ones.

There is very little that can be wrong with the wiring that will damage the Engine Computer. The biggest threat is if the 5.0 volt supply wire to most of the sensors is grounded, but the computer will simply detect that and shut the supply down to protect it. Once the short is removed, you just turn the ignition switch off and back on to reset it.