TBI 3-wire O2 sensor upgrade, no open loop

I have a 1987 TBI 350 with long tube headers. I bought a harness off Ebay and to upgrade from a 1 wire O2 sensor to 3 wire to help go into closed loop in the winter. The new sensor stays between about 440 and 460 mv and the truck won't go into closed loop. The sensor is heating up and its getting 12 volts. Anyone else have this issue? Any recalibration or "reset" needed? I am also running EBL Flash. When I put the 1 wire sensor in, the truck will run closed loop.

The 3 eire sensor is p/n 0258003077 Maybe I shoild use another?

Sounds like the harness is pinned wrong or the sensor is faulty.

450mv or there close is what the ECM sees with the sensor return disconnected. Most likely wiring issue as sixshooter mentioned.

Thanks. I may cut theharness off and just solder it in and see what happens. If that doesn't work, I can get another sensor. Thanks.

Don't cut the plugs off. Just look at the female terminals to see if they are still closed and will make a good connection to the female terminals.

As for checking the wiring. Look at the sensor wires, not the plug wires. The 2 wires the same color are the heater wires. The different colored wire is the signal output wire.

Good thread, I was able to xref that part number to OEM applications and now I can get a heated O2 sensor much less expensively, to use on my driver's side manifold for tu ning... another box to check on the project!

You can only use that narrowband O2 for closed loop tuning. If you already have an O2 sensor for feedback into the PCM then it's rather pointless to add another one for tuning.

Overall, I'm not a fan of 3-wire sensors for any use. The 4-wire sensors are a similar price and that way you're not relying on the exhaust and engine block to be the ground for the sensor.

I already have a 1-wire O2, in the downpipe where they all come together, stock location for the 4.3L V6 I sourced the y-pipe from (had to mod it to fit the V8).

I also have an available port at the driver's side head which is presently blocked with the old, broken O2 I took out of the above port.

I don't see any reason not to use that port for a (ok, 4-wire, like your point about the ground) O2 specifically for tuning. Folks on this board who know much more about tuning than I have suggested this approach.

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Originally Posted by 89S10_Project

I already have a 1-wire O2, in the downpipe where they all come together, stock location for the 4.3L V6 I sourced the y-pipe from (had to mod it to fit the V8).

I also have an available port at the driver's side head which is presently blocked with the old, broken O2 I took out of the above port.

I don't see any reason not to use that port for a (ok, 4-wire, like your point about the ground) O2 specifically for tuning. Folks on this board who know much more about tuning than I have suggested this approach.

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a narrowband that isn't part of the closed loop trim system is practically useless...

I believe you are mistaking a narrowband O2 sensor for a wideband O2 sensor. You use a separate wideband O2 sensor for tuning.

Basically, 1 wire O2 sensors have to be within so many inches of the head-they're great for stock manifolds and the like because they rely on the exhaust gas to heat them up and keep them at temperature. Once you go to a long-tube tubular header, the exhaust gas temperature drops too much to reliably heat the sensor-so you go to a 3-wire or 4 wire sensor, incorporating a heater element to keep the sensor hot enough to function.

Outside of the added heater, and the separate signal ground for the 4-wire, there is zero difference between a 1 wire, 3 wire, and 4 wire narrowband O2 sensor. they function identically to each other, and are useless for open loop tuning.