The car is my '86 900 8valve sedan. After removing/reinstalling all my turbo piping, changing out the battery cable to the starter (which was cracking and falling apart), and removing/cleaning the grounds on top of the engine, my rpms now do not register at all. The car starts, runs for around 5 seconds and then dies, presumably from the same issue that is causing the AWOL rpms. I've removed the hall sensor connector to verify that it is not in fact the hall sensor, after which the car would not start at all (as predicted). Plugging the hall sensor connector back in, the car starts and dies after 5 seconds again. If you hold the throttle down, it will run at high rpms for a bit longer. What sends the rpm signal?