when I got my TII engine, the O2 sensor wasn't connected because the wire is broken. now I'm trying to chase it down so I can get better gas mileage.

so my question is, on an 87' TII, where does that wire go after the 02 sensor? like, where does it go in its path from the wiring harness to the sensor?

I looked under the IM like where it goes on my N/A, but I couldn't find any broken wires or loose plugs. the only one I could find was on that went toward the passenger side strut tower. could this be it? it looked like a pretty big wire though.

I'm hoping to find this without taking off the IM, but If I need to I will.

-travis

 

It's wire comes out of the same harness as the BAC valve.

 

will an engine run, if so well, without the sensor plugged in???

 

Yes, it'll run just fine, it'll just not go into full-loop mode or whatever and use up more gas

 

Closed-loop.

 

If you untape the wiring harness, look for a wire that has a shielded cable inside. This will be the O2 wire. When fixing, do not allow any strands of the shielded cable to come into contact with the O2 wire, or it will put it to ground, no signal.

 

what the frick is closed loop suppose to mean?

 

yes!! I found it. so about how much better MPG should I expect to see? (assume the sensor is in good condition)

 

I saw no difference when mine was unpluged. if you are lucky you might see 5-10% better. it really doesn't do much

 

well damn. I hope mine does work better. thanks

 

EFI runs in two main modes, open-loop and closed-loop.
Open loop means the ECU measures airflow and rpm, and looks looks up in its internal maps to see how much fuel is required to be injected for those conditions. It then adds correction factors for things like air and coolant temps. The O2 sensor is ignored.
When the engines under light load (cruising) it starts looking at the output of the O2 sensor as well. If the mixture's richer than stoichiometric (the ratio of air and fuel for perfect combustion and maximum economy) it'll lean it out. If it's leaner than stoichiometric it'll enrichen it. It does this many times per second so if you're watching an A/F gauge when the ECU does into closed loop you'll see it cycle rapidly back and forth around the middle of the scale.
This is one of the things that make EFI more fuel eficient than carbs. Like scott said the savings would be around 5-10% (depending on how you drive), but that's a pretty good saving if you ask me.