The Power Transistor Unit (PTU) is in a sense and On/Off switch for the coil pack. The ECU sends a GROUND or NO GROUND signal to the PTU. When the PTU receives a NO GROUND signal from the ECU, it will send spark to the corresponding coil. Either coils 1 and 4 or 2 and 3. When the PTU receives a GROUND signal from the ECU, it stops sending power to the corresponding coil.
A faulty PTU will cause a no spark issue.
If you’re having a no spark issue, a good place to look would be the PTU. First off make sure its plugged in tight. These connectors and units are 20+ years old most of them. Over time they become worn out causing them to come loose from even normal engine vibrations. Alot of people reported their cars shutting off during a pull. A loose PTU connector is often linked to this. If your PTU plug is tight, it may be faulty. Test the coil pack while cranking to see if its getting power. If not, it may be the PTU. Now the easiest way to check and see if your PTU is bad is just to swap it with a known good one. But there is ways to test it. It is recommended you use an analog ohmmeter. Digital ones cannot read the transistor as accurately as an analog meter. Also, temperature is a factor. A cold PTU may work properly but fail after the engine warms up. Test the PTU first while cold then test again warm. Use a heat gun or a hair dryer to warm it up.