Alright, I installed a 3-wire O2 sensor from an 84' 300ZXT. Or I should say I ordered a universal bosch 3-wire for an 84' 300ZXT. Anyway I got it all installed I spliced one heater wire into the green wire that powers/heats the air regulator, and then I spliced the other heater wire into the ECU ground wire that gets ground on the intake. I don't know if this is what did it, or also a combination of a bad O2 sensor or what, now my car runs completely horrible. With the wires hooked up and the ignition on the power wire was getting battery voltage, the other heater wire was getting like .14v. I looked through the 84' Z31 FSM, the heater looks like it has it's own ground and should get battery voltage with ignition on. Heater wire gets that if I connect it to it's own ground. If I check the voltage on the ground wire it's getting that .14 voltage or lower, is the ECU supposed to have a really low voltage across the ground? Maybe that's why the air regulator and O2s use their own ECU ground? Can anyone check what voltage they get off any of the ground wires to the intake with the ignition turned on?

 

Why are you using a 3 wire Z31 O2 sensor?

 

To help get the car into closed loop sooner. Since all the Z31s used a 3-wire heated, it helps when it gets cold around here.

 

Are you sure it's the right O2 sensor wire you hooked into the air regulator wire?

I'm looking at my 84 Z31T ecu wiring diagram and I don't see ANY O2 sensor grounds...

Black shield wire goes to ecu pin# 24 (A/F signal)
Blue connects to air regulator
Yellow connects to ecu pin# 115

None of them are grounded to the body / motor.

 

I think the 115 pin acts as a ground. When the FSM has you test it you remove that ecu connector with ignition on, put the multimeter into pin 115 and put the other end to a ground. So I assumed that was the ground, but even so, I'm going to just put my 1-wire O2 sensor in and put everything back the way it was and see if I go back to normal. I'm thinking the O2 sensor itself may be dead. I did the heater test and it was giving out a higher ohm reading than was in spec in the FSM. The A/F gauge never started bouncing around at any point either.

I just pulled all the 3-wire O2 wiring out, put everything back, took the heated sensor out, put my 1-wire back in. Pulled the battery cables to let it reset. Hopefully things will be ok.

Should have gotten an NGK O2 sensor. I've read a bunch of people on hybridz say that the NGK O2 sensors are better for some reason.

 

Well it was a fun combination. Switching back to the one wire O2 sensor car still ran like crap, but was a lot more tolerable. I started looking around and found out my el' cheapo blow-off valve was staying open at idle and sucking in nice amounts of air.

 

Hopefully getting the blow off valve to seal will solve your idle issue. NGK or Bosch o2 sensors are fine. I'm using a Bosch sensor for my wideband and standard narrow band with no problems. Is your Z stalling out?

 

It was stalling out. After I went back to the single wire O2 sensor my car was still acting really odd, but it was much more drivable then it was. I noticed while driving the A/F gauge started bouncing like it was supposed to. It didn't bounce at all with the 3-wire. As it was attempting to bounce around it was really erratic, and it could never actually make it to the green rich section. So I pooped the hood, and was checking around the cheapo blow-off valve. Found it was sucking in air at idle. Removed it, and then my car went back to normal. Although it looks like I have caused some sort of vacuum leak, as my vacuum is now a bit lower at idle than it was a day or two ago and idle is still a little shaky, but it's better then it was.

3-wire heater definitely didn't ohm as the FSM stated which leads me to think it was a bad O2 sensor.