Yesterday while taking the RX7 around the block for the first time of the year, the oil pressure gauge pegged. When I got home I did some basic diagnosis - engine off, key on it pegged. Unplugged sender, still pegged when the key turns on. Problem is not in the sender.
Into the service manual I went for the wiring diagram. There is a capacitor in parallel to the sender - perhaps that went bad. I go to look and...
... the wire broke off the body of the capacitor and was laying on the engine, shorting the 12v sense wire to ground. Tape off the end of the wire, key on, gauge doesn’t peg.
Here’s the problem though - I started the car, very low reading. If you rev it up it would move some, but it sat just off of zero instead of mid-scale where it usually would be at idle. Back to the service manual, 200 ohms should be the first tick mark, 150 ohms around mid-scale.
After checking the wiring for integrity and other such basics, I unplugged the sender and clipped a 150 ohm resistor in its place to ground. Key on, and the gauge sits just above zero. Shit.
So what does this all mean? When that wire decided to pop off the cap and ground itself out, it seems to have burned out the winding of the gauge movement. On the most important gauge in the car.
Anyone have an 84-85 RX7 cluster laying around with a good oil/volt unit?