Installed 3-Wire O2, now problems

[DuoWing]

280ZXT with 84 ZXT ECCS. I installed a 3-wire O2 to help with warmup period. Ordered a universal bosch 3-wire for an 84' ZXT. Spliced one heater wire into green wire that feeds power to air regulator from Fuel Pump Relay. I spliced the other heater wire into the ECU ground wires. Now I have a bunch of problems. I'm wondering if I just screwed up the wiring.

I checked the power wire and with ignition on I was receiving battery voltage, the other wire was like .14 volts or something of the sort. I don't know if that indicates a funky O2 or just a wiring issue. Could the fact that the O2 sensor heater doesn't have polarity cause an issue with the ECU grounds?

[TimZ]

Could the fact that the O2 sensor heater doesn't have polarity cause an issue with the ECU grounds?

 

On a 4-wire EGO the heater is separate and doesn't have polarity. On a 3-wire EGO the heater shares the ground with the sensor output, so it does have polarity.

 

Also, since the heater can take a fair amount of current it would probably be better to feed it its own power and ground rather than trying to use existing wires of unknown current capacity.

[DuoWing]

Would it be possible for the O2 sensor to be messed up to the point that it can really cause me to run really poorly? Is it possible that tapping the heater wire into the ECU ground could screw something up?

[Xander]

On a 4-wire EGO the heater is separate and doesn't have polarity. On a 3-wire EGO the heater shares the ground with the sensor output, so it does have polarity.

 

Are you sure about that? I always thought that a three wire sensor had a signal wire (black) and two heater wires (white). It grounds via it's connection to the exhaust.

 

check this site for reverence

 

http://www.tomco.co.uk/PAGES/Technical/oxygen%20senors/refchart/refchart.htm

 

PS: I beleive the 300zx had that weird titanium sensors.

[TimZ]

Are you sure about that? I always thought that a three wire sensor had a signal wire (black) and two heater wires (white). It grounds via it's connection to the exhaust.

 

check this site for reverence

 

http://www.tomco.co.uk/PAGES/Technical/oxygen%20senors/refchart/refchart.htm

 

PS: I beleive the 300zx had that weird titanium sensors.

 

Apparently I was mistaken on the polarity thing - however I'l still stand by the other comments - I would not recommend splicing the heater into the existing wiring, and especially not into the ECU ground.

 

Introducing a significant amount of current into the ECU ground is very likely to cause a ground shift and potentially mess up many if not all of its sensor readings.

[Tony D]

When I hooked up mine for the MS, I used a 300ZX 3-wire, and wired it into the fuel pump relay circuit. It is only getting power when the fuel pump is running.

I used the Z31 connector, and wired it according to the Z31 FSM wiring diagram, meaning the signal had a shielded wire back to the ECU, with the other two being power and dedicated ground.

 

I will have to check into that current limiting resistor JeffP mentioned, I have never seen excessive draw, but it may be wise to limit current downstream by such a method.

 

I hooked it into the Fuel Pump circuit because I only want power on it when it's running. If you were worried about power draw on existing circuits, it's simply a matter of putting another relay into the circuit, and using the fuel pump power wire be the one that triggers the 'heater circuit relay' you install with a direct line from power to the sensor (through whatever current limiting resistor you deem appropriate) and then on to it's own discreet ground.

[DuoWing]

I'd like to get a hold of a connector and some wiring fro the Z31 O2 sensor. Anyway I removed the 3-wire, put the 1-wire back in. Car still ran like crap, but at least now it was drivable. I also found that my cheapo blow-off valve had decided to fail open at idle. It was drawing in mass amounts of air, so this was the biggest part of my problem, but oddly enough the O2 sensor was bad and just adding to the problem.

 

I was thinking what I'd do, is I connect the black signal wire to the existing shielded signal wire for the 1-wire O2 sensor. I also ran the heater power through the fuel pump relay circuit so it would only be receiving the heater current when running. I think I may just add another pin and run the other heater wire into pin 115 on the ECU as that seems to be made for the O2 as pin 16 seems to be solely for the Air Regulator.

 

From what I've looked up the 300ZX did use 3-wire titania, but that was the 86+ turbo cars. All the others used the 3-wire Zirconia which fit into the existing threading on my downpipe.