74 Dart Sport Spark Issue

Disconnect the connector from the ECU and check to see if any of the contacts are spread and possibly not contacting the ecu pin.

If that looks good, hold the connector so that the pin pattern looks like a pentastar, pin #1 will be on top center, #2 will be the next in a clockwise orientation, #3 under #2, #4 opposite #2, and #5 opposite
With the key in "run" pins #1,2,and 3 should be within 1 volt of battery voltage. If not, find the problem and repair it (possibly the ballast resistor).
Also, pull the connector off the starter relay so the starter does not engage, check for battery voltage at coil + terminal with the key held in "start".

Connect an ohmmeter between pins #4 and #5 with the distributor connector connected, the reading should be 350-550 ohms. If this shows an open, your wiring is broken between the ECU and distributor or you distibutor pickup is faulty.

If this all checks out ok, check for approx. 1 volt AC pulse at the distributor connector when the engine is turned over (disconnect the distributor connector and connect the multimeter directly to it)

If everything checks out ok, check the air gap on the distibutor reluctor, it should be .008". If there is too much gap it may not trigger the ECU.

Another handy way to check spark without spinning the engine over is to pull the distibutor out and reconnect everything to it, then just spin the distributor shaft by hand with the key in "run" and the coil wire near the block, it should spark.

A couple years ago, I got some defective Ecu's from the parts store. I tried three before I just gave up on that brand--every time I put a new one on there was no spark and when I put an old spare I had on, there was spark again.

Good luck on your troubleshooting, hope this helps.