3.2 O2 sensor

[dhw]

I have a 75911s with an 88 3.2. I was installing a new O2 sensor and realized that the harness connector had been removed and the wires connected with crimp connectors. I have had some performance issues that seem like they could be realted to the sensor (hence why I was replacing it) but now I am thinking that it might be wired incorrectly.... The new O2 sensor has two white wires and a black wire. Does anyone know which these correspond to on the ecu side of the harness?

[rcaradimos]

The black is the sensor lead and the two whites are the leads to heat the sensor, that's how I understand it. I'm sure someone can confirm.

[Jeff]

dhw, what kind of performance issues?

Welcome to the board.

[nhromyak]

As I recall the O2 only does idle (perhaps cruise as well)... Everything else is based on the mappings of the DME (Acceleration Enrichment, Power Enrichment etc.)

Hence, I beleive the O2 does fuel economy not performance.

[dhw]

thanks for the welcome...
inconsistant surging idle hot and cold as well as lackluster low end performance.... mild hesitation in the low 2000's

[nhromyak]

Could be a CHT, leaky intake gaskets, or idle set switch.

You can get an idea of the O2 sensor is working by connecting it and disconnecting the black wire. This tends to bring the idle up on mine when it is disconnected as the car goes more rich.

You could also test the output voltage of the O2 sensor. But of course, this is one small equation of what an O2 sensor actually does. The computer is only looking for and relying on the speed of hysteresis (swinging of the voltage across .5 of the O2 sensor, which is difficult to measure.

Good luck.

[dhw]

ya the surge is wierd, its almost as if the car almost dies and then surges up to about 1800-2000, then almost dies again. It will do this for consistantly at a stoplight, and then be fine at the next stop light.... Sometimes tapping the accelerator helps but not consistantly enough to give any clue as to if it what fixes it.

[nhromyak]

Check your idle set switch for contact and connectivity all the way back to the DME computer.

Good luck.

[ianc]

As I recall the O2 only does idle (perhaps cruise as well)...

IIRC, the O2 sensor affects everything (as long as it's warmed up) except when the WOT switch engages.

ianc

[Lorenfb]

"the O2 sensor affects everything (as long as it's warmed up) except when the WOT switch engages." - ianc -

Ian is right on!. The problem occurs though if the system parameters are
significantly out of range, e.g. fuel pressure, temp sensor, or the AFM.
The DME Lambda control system is limited in how much it can lean or
richen the mixture. That's why the '96 and later cars with OBDII can
make mixture changes to allow the Lambda system to operate within
its controllable range, but that also has limitations in the corrections it
can make.

[Jeff]

Check the CHT - check for cracks in the wire and make sure it is the two wire unit, if not replace it. I don't have my manaual in front of me so I can't give you the specs to measure, I will look it up in a little while.

Also as Nick said check your Idle control switch. Un plug it and check for continuity everywhere but closed.

[dhw]

thanks I'll check that stuff out.....

[Jeff]

dhw, something else to look at for the idle problem is the Idle control VALVE (not switch). These can be taken apart and cleaned with Isopropyl. There is a plunger inside that can get jammed up with gunk and keep the idle from coming back to normal.

Good luck and let us know what you find.

[dhw]

the valve was the first thing I checked hoping for an easy fix for this one....