Replaced all relay's, ECM and Coil but have no spark. All fuses are good. Battery new and has a healthy charge. All conections have been checked and double checked. Suggestions welcome.

Yes, the ECM is the last thing to replace after all other possibilities. No spark could be bad ignition coil, bad Ignition Control Module (controls the coil circuits for spark), bad plug wires, the crank and cam sensors (for ECM to determine spark timing).

Check the ICM -it can be tested at a parts store. If good, check the crank sensor.

Need to know what kind of car, engine etc

How About the CPS Crank Shaft positioning sensor? otherwise Sounds Like( Im Not Sure what you are saying you replaced the ECM) Electronic Control Module) ? Or Electronic Control Unit? Otherwise Checking to make sure you have a good ground from the battery to the motor to firewall as well,also im pretty sure there is a switch in your fuse box for the ignition and fuel pump last but not least coil could be bad even though you have ohms and how many ohms?(ps you said you forced spark thru hooking strait up to positive you got little Spark when you did that? if you did sounds like ground or low voltage or Bad Coil !! have you hooked up and tried to pull a code ? I hope this helps!!

if all you did was this...and and put a new battery in and still wont start...if you have went thru your plugs..wires..distributor..ignition coil...made sure your getting spark..if not..check your relays and fuses..preferebly one that deals with spark and timing for injectors..if everything is fine to that point...then try a crankshaft position sensor...it tells the pcm timing for fuel injectors and fire to the ignition coil...hopefully this helps.

The fuel pump and coil are on two different circuits.
The fuel pump is on the 20amp ECM fuse and the coil, ignition module, and injectors are on a 20amp fuse #10. But the ECM fuse could keep the coil and injectors from working.
You would need to test the fuses in the box in the engine compartment, and the fuel pump relay and coil for voltage and ground. The pump relay is grounded by the computer for 3 seconds when the engine is cranked.

Is it Fuel injection and electronic ignition, or still distributor and carb?
if its FI, check the fuel relay, located in the fuse box usually, not sure where for your truck specifically, but if you locate it, tap on it a few times while someone else cranks the truck, also, the fuel pump could be faulty, can you hear the winding noise when you turn on the ignition, if not, then pump is gone.
The spark issue is a tricky one since you said you have replaced the coil... spark wires ok? coil installed properly? battery charged and leads tight? alternator working? if alternator is failing to charge the battery, then it gets to a point where you dont have enough power to make the coil spark, the engine will crank, but not enough current (amps) to fully charge coils to deliver healthy spark.

Good luck...

1. does it turn over? if so, strong, or weak? 2. did you replace the fuel filter? 3. coil packs, or distributor (pack(s) can be tested) if distributed check cap and rotor, replace coil, but first check starter relay - 4. Check all ignition fuses, starter fuse - (along with relay{above}) 5. Check all connections from battery - positive, negative etc.
Please let me know if you need further assistance.
carsandcomps,
Guru, Premium Expert @ Fixya.com

Dear Sir,
As you saying you have replaced ignition coil and crank sensor, next is check relay fro ignition system in fuse box replace relay with other one for testing purpose only, if no change then next,if you can check continuity of all wire form Engine Control Unit to Ignition coil, if all wire are ok then replace Engine Control Unit (ECM) if any wire found no contunity please reconnect same wire or repair wire it will solve problem if not then you have to replace ECM. thanks.

the crankshaft position sensor located between flywheel and trans is where the power source for the coil comes from. I suggest you need change that

have you checked the crankshaft sensor? thats what gives it spark to the coil then to the plugs