so my buddy has a crazy problem going on. his 94 fd is throwing code 05-knock sensor but will come on and off at random times. the other day when the check engine light was on he rolled his wondow up and noticed the cel went off.?. and came back. conclusion is when cel is on if you roll the windows down/up, turn the lights on, rear defroster the cel will be off but come back on if you take your finger off the window switch or turn the lights back off.

 

wild guess: something is not grounded or grounded intermittently.

 

That's a good guess, rousu. The Knock sensor is a one-wire connector for signal, and it gets grounded through the engine. So the ground for the knock sensor takes this path: (sensor>>engine>>battery) . At some point, all those other things (defroster, windows, lights) get grounded to the chassis which gets grounded to the battery. Electricity tries to take the path of least resistance so if the ground wires those other things usually use (defroster>>chassis >> battery) are not connected well, the electricity may try another path such as (chassis >> engine >> battery). The electrical manual shows ground locations pretty clearly, but feel free to post if you've got questions after reading through it. There should be a link in the FAQ thread: https://www.rx7club.com/3rd-generati...l-links-68640/