Got a new one from Rock Auto this week, and I put it in earlier this evening. It made the gauge behave the same exact way.
So I got down to diagnosing. Multimeter came out. FSM came out. Original OEM and recent O'Reilly brand senders came out. FSM says which wire should be ground and power. Check... FSM says what the resistance in the sensor should be at 0 psi, 17 ohms. Freshly removed "BAD" sensor shows 4.6 ohms. Hmm. I reach in and test the new sensor, and it shows 4.7 ohms.
Ok, recent O'Reilly unit shows 0.6 ohms. Odd, that'* even further from 17 ohms. Old *** original shows 0.8 ohms.
I put the original back in... and wouldn't you know it, it works just fine. It always did, but I just wanted a fresh one, so that'* why I got the O'Reilly unit. And just recently decided I didn't trust it too much, even though it seemed to work fine. That'* why I ordered a new AC Delco unit.
So, now my question is... does my car just need a different sensor then AC Delco thinks it does? Are they both actually bad? The only visible difference between the two that work for me and the two AC Delco units is body length. The original and O'Reilly are about 3.5" long, and the AC Delco units are 2" long.
Any one have a known good sensor they can check the resistance of?