Does the 3 Wire feedback carburettor on 1985 Nissan 720 support having an O2 Sensor?

[datzenmike]

Part if the F. I. C. D fast idle control device. It's missing, but mounts in the circular hole and increases idle speed when air conditioner is on

[Doomedwalker]

12 minutes ago, datzenmike said:

Part if the F. I. C. D fast idle control device. It's missing, but mounts in the circular hole and increases idle speed when air conditioner is on

OK thanks, My truck doesn't have AC. i have one of those dash-pots came with my Trucks original Carburetor.

[datzenmike]

Dash pots prevent sudden abrupt closing of the throttle on automatics which can cause stalling.

[Doomedwalker]

4 minutes ago, datzenmike said:

Dash pots prevent sudden abrupt closing of the throttle on automatics which can cause stalling.

 

yeah the truck used to be automatic.

[Smoking Joe]

I have a Six wire carb with computer under the drivers seat along with an O2 sensor in the exhaust manifold. My factory service manual says that after 90,000 miles to disconnect the sensor when the dash sensor light comes on. My truck has about 180,000 miles and the sensor light is obviously on. So during my rebuild of the engine I only to simply unplug the sensor and

hopefully the light will

no longer be illuminated.  My question to the forum should the truck still run as before which was excellent after disconnecting the sensor and the obvious electronic changes to the carb will no longer be active. 

[Thomas Perkins]

8 hours ago, Smoking Joe said:

I have a Six wire carb with computer under the drivers seat along with an O2 sensor in the exhaust manifold. My factory service manual says that after 90,000 miles to disconnect the sensor when the dash sensor light comes on. My truck has about 180,000 miles and the sensor light is obviously on. So during my rebuild of the engine I only to simply unplug the sensor and

hopefully the light will

no longer be illuminated.  My question to the forum should the truck still run as before which was excellent after disconnecting the sensor and the obvious electronic changes to the carb will no longer be active. 

You did right.That just cuts the light off.

[datzenmike]

You do not want to unplug the O² sensor. Unplug the light.

[Smoking Joe]

18 hours ago, datzenmike said:

You do not want to unplug the O² sensor. Unplug the light.

Mike I'm not even sure the sensor is still working when it was plugged in.  I hear what you're saying and please understand I'm not trying to argue your comment I'm just trying to understand, But the FSM states that during 30 / 60 and finally 90,000 miles to unplug and leave unplugged. Granted that's very confusing for me to understand as to why they would utilize an item such as an O2 sensor and then recommend the infinite disconnection of it after x amount of miles.  

[Thomas Perkins]

51 minutes ago, Smoking Joe said:

Mike I'm not even sure the sensor is still working when it was plugged in.  I hear what you're saying and please understand I'm not trying to argue your comment I'm just trying to understand, But the FSM states that during 30 / 60 and finally 90,000 miles to unplug and leave unplugged. Granted that's very confusing for me to understand as to why they would utilize an item such as an O2 sensor and then recommend the infinite disconnection of it after x amount .

Just another bad idea Nissan had back in the day.Also you will see a few connectors under the hood that is not used.Will make you think...

Edited May 27 by Thomas Perkins

[datzenmike]

2 hours ago, Smoking Joe said:

Mike I'm not even sure the sensor is still working when it was plugged in.  I hear what you're saying and please understand I'm not trying to argue your comment I'm just trying to understand, But the FSM states that during 30 / 60 and finally 90,000 miles to unplug and leave unplugged. Granted that's very confusing for me to understand as to why they would utilize an item such as an O2 sensor and then recommend the infinite disconnection of it after x amount of miles.  

 

YES unplug the light. The O² sensor has to be functional or the system will revert to an over rich limp home mode and waste gas.

[Doomedwalker]

21 hours ago, Smoking Joe said:

Mike I'm not even sure the sensor is still working when it was plugged in.  I hear what you're saying and please understand I'm not trying to argue your comment I'm just trying to understand, But the FSM states that during 30 / 60 and finally 90,000 miles to unplug and leave unplugged. Granted that's very confusing for me to understand as to why they would utilize an item such as an O2 sensor and then recommend the infinite disconnection of it after x amount of miles.  

keep the sensor plugged in and or get a new O2 sensor.

[Sephakrid]

On 5/22/2026 at 12:06 PM, Doomedwalker said:

 

i cannot afford anything much better, than 25 to 50 bucks where i sit financially, 

https://www.amazon.ca/Shkalacar-Narrowband-Volmeter-Modification-Accessories/dp/B0CND18DC1/ref=zg_bs_g_9163877011_d_sccl_41/139-4532569-6837822?th=1

 

also do you know what turning this with the big spring on it does?
its not the hi idle.

I believe that screw is for adjusting when the throttle switch activates. Sometimes after adjusting idle RPM, the throttle switch may activate either too early or not at all. 

[Doomedwalker]

44 minutes ago, Sephakrid said:

I believe that screw is for adjusting when the throttle switch activates. Sometimes after adjusting idle RPM, the throttle switch may activate either too early or not at all. 

i think mike has the right answer, i am pretty sure its useless on my truck as i dont have AC.