Why i don't have any rpm reading 98 deville?

If your 1998 Cadillac DeVille isn't showing any RPM readings, it could be due to a faulty engine control module (ECM), a defective tachometer, or issues with the wiring or connections to the instrument cluster. Additionally, a malfunctioning crankshaft position sensor can prevent the RPM signal from reaching the tachometer. It's advisable to check for any diagnostic trouble codes (DTCs) and inspect the electrical components to identify the cause.