Just wait
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1st Gear
Joined: Apr 2024
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From: Eugene Oregon
Just wait
Hey all. I’ve got an 85 bronco 4.9 I6. Just got it last weekend and have started to do some maintenance on it. I noticed my O2 sensor wiring is cut about an inch off the sensor and I can’t seem to find where to plug the new one into. Anyone got pictures or description of where I should splice or plug?
Mountain Pass
Joined: Dec 2020
Posts: 109
Likes: 12
The I6 forum might be better for this question.
My guesses and 2 cents:
- 85 probably originally used a feedback carb. I don't know what electronics controlled that - EEC-III maybe?
- Since there isn't any obvious wiring for the O2 sensor, someone may have swapped out the feedback carb and its controller for something else, e.g. a non-feedback carb.
- Personally, I'd be inclined to use a regular old non-feedback carb if there wasn't some great reason to use a feedback carb (e.g. punishment from the Peoples' Emissions Commissar) as it would be easier to source parts and troubleshoot.
- And in that case, I'd also consider putting a wide-band O2 sensor in that hole and an AFR gauge on the dash to assist in tuning, future troubleshooting, and driving for fuel economy.
My guesses and 2 cents:
- 85 probably originally used a feedback carb. I don't know what electronics controlled that - EEC-III maybe?
- Since there isn't any obvious wiring for the O2 sensor, someone may have swapped out the feedback carb and its controller for something else, e.g. a non-feedback carb.
- Personally, I'd be inclined to use a regular old non-feedback carb if there wasn't some great reason to use a feedback carb (e.g. punishment from the Peoples' Emissions Commissar) as it would be easier to source parts and troubleshoot.
- And in that case, I'd also consider putting a wide-band O2 sensor in that hole and an AFR gauge on the dash to assist in tuning, future troubleshooting, and driving for fuel economy.
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
Not positive but I believe Bronco never got the EEC3 Variable Venturi feedback carb (thank god) Cali emissions maybe
His 1985 should be fuel injected either way
Not sure about the O2 sensor wire location myself on that 85 Bronco
Most of the early ones exited the cab behind (near) the seats (single wire connector) or came out of the main loom by the HVAC case IIRR
EEC 3 was the VV carb era 1981-1983 (EEC1 2 and 3)
EEC 4 was started in '84
By 85 the 5.0 was fuel injected IIRR and the big block 7.5 was mid year 86 for its fuel injection
Get a new single wire O2 sensor (new old stock Motorcraft or Ford)
Some of the early (one wire) sensors picked up their O2 reference signal from the wire to plastic insulation gap
Meaning, if you repair the wire with solder or a butt connector it renders the sensor inop
His 1985 should be fuel injected either way
Not sure about the O2 sensor wire location myself on that 85 Bronco
Most of the early ones exited the cab behind (near) the seats (single wire connector) or came out of the main loom by the HVAC case IIRR
EEC 3 was the VV carb era 1981-1983 (EEC1 2 and 3)
EEC 4 was started in '84
By 85 the 5.0 was fuel injected IIRR and the big block 7.5 was mid year 86 for its fuel injection
Get a new single wire O2 sensor (new old stock Motorcraft or Ford)
Some of the early (one wire) sensors picked up their O2 reference signal from the wire to plastic insulation gap
Meaning, if you repair the wire with solder or a butt connector it renders the sensor inop
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