97 Dodge Ram Pick up cranks ok engine won't run

Are you missing anything else? Engine cranking, you have fuel injector pulse?
At your ignition coil, brown wire with white tracer, should be hot engine cranking. Probably the same color wire for voltage at your fuel injectors. Use a test light to check for voltage.
If no voltage, check signal from cam and crank sensors. Some of these vehicles the computer has to see proper signals from both the cam and sensor or it won't ground the asd relay. The asd relay sends voltage to several systems including the ignition coil and fuel injectors. Any applicable trouble codes?

Make sure battery has a full charge. Did you check primary voltage to ignition coil, engine cranking, dark green wire with orange tracer? Use a test light, is it hot? The voltage comes from asd relay, check voltage and ground circuits. The load side of relay is that line with arrowhead, that circuit is fuse protected and hot all the time. The control side of relay is the left side in diagram, has to have voltage and ground. The voltage appears to come from ignition switch on or cranking. Grounded by computer.
The distributor has a sensor in it that sends rpm signal to computer, w/o that signal the computer won't ground the asd relay and you get nothing. The asd relay sends voltage to several systems. Just my opinion. Any applicable trouble codes?

Primary voltage to several systems, including the ignition coil, dark green wire with orange tracer. That voltage comes from asd relay. There is a fuse for asd relay. To check for voltage the engine has to cranking. The control side of asd relay, the computer has to ground it before it will energize. Did you check wiring circuits for cam and crank sensor connectors before replacing sensors? Are there any applicable trouble codes?
Are you ok with testing wiring circuits?

You don't do an ohm check . Hook a test light to battery positive an have someone crank the engine over an touch the point part of test light to the PCM circuit at the relay socket . If the test light light's the PCM is grounding the circuit . Watch this video ! Fuel Pump Electrical Circuits Description and Operation ASD relay chrysler

Note the diagram. The left side of asd relay, line with arrowhead, is load side of relay, when the relay is energized that line moves to other terminal and it carries voltage to everything the asd relay controls. The control side of relay, right side, is that coil symbol, that side needs voltage and ground. The computer grounds the control side of relay if it sees proper signal from crank and cam sensors. Not only check those fuses, use a test lite check fuse circuit for voltage, as you can see, one fuse is hot all the time, the other goes hot with the key on.

are you sure that you changed the ASD relay? that code is for no signal from the ASD to the PCM. Check that you have constant 12v at the relay base and that you have switched voltage when the key is on at the relay base, then make sure you have continuity to ground at the relay base. If the relay clicks when the key is turned on then the internal coil is making and should be sending a signal to the PCM when the key is turned on.

First thing to check is the ASD relay and voltage at the coil.

If you cannot read codes, it is most likely because the computer is not "turned on". What I mean by that is there are 3 battery feeds and 3 ground circuits to the Powertrain Control Module (PCM) If any of these circuits are not working, the PCM will not communicate with a scanner. It is like trying to turn on a lamp that is not plugged in...it simply will not work. Don't go out and buy any parts or replace ANYTHING until you have your communication problem resolved. You will only be wasting time and MONEY otherwise. For instance, why on earth would anyone replace a crank sensor on an engine when the PCM is obviously malfunctioning? This can get VERY EXPENSIVE! Most likely, if you fix the faulty power or ground circuit that is stopping your PCM from communicating, you will fix your car.

I can help you test your circuits to find the problem, but the circuits are a little different between the 3.3L engine and the 3.5L engine and you did not mention which engine your vehicle is equipped with.

Please read these two articles and get back with me if you would like further assistance:

Where's The Fuse?

What Else Could Be Wrong?

P0685 DODGE - Auto Shutdown Relay Control Circuit Failure
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)

Possible causes - ASD relay circuit is open or shorted
- Failed Auto Shutdown relay
- Failed ECM
Tech notes Check all the ECM fuses, if the fuses are OK try replacing the ASD relay. P0685 DODGE Description Short or open in Auto Shutdown (ASD) relay circuit

P0688 DODGE - Auto Shutdown Relay Control Circuit Low
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)

Possible causes - ASD relay circuit is open or shorted
- Failed Auto Shutdown relay
- Failed ECM
Tech notes Check all the ECM fuses, if the fuses are OK try replacing the ASD relay. P0688 DODGE Description The Front Control Module (FCM) has detected the supply voltage below an acceptable value

crank sensor, ignition module or computer,

Take your pick without any testing.

Or possible ASD main relay in undershood fuse box.