Oxygen Sensor

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O2 (oxygen) sensors can be used to troubleshoot the fuel/air mixture. This uses an Oxygen sensor (Lambda sensor) to display to you how the actual a/f ratio of the engine as it is running. This is good for carbureted cars too, so you can see which way you need to adjust or jet the carb.

Overview

For O2 sensor use in EFI systems, see Fuel Injection

Most O2 Sensor read only rich vs lean. That's enough for EFI control, or for a rich/lean (red/green) gauge.

For an actual air/fuel ratio number you need a wideband O2 Sensor, also called an "Air Fuel Ratio Sensor".

Testing

You can test the O2 sensor while the car is running. Basically, you can tap in to the existing wire for the sensor. You can get a high-impedance ohmmeter at radio shack for under $40, but the specs need to be 20 Mega ohms resistance (most are not this high). Regular Ohmmeters will short out the sensor.

Rich/Lean Gauge

Rich/Lean gauge will tell you if the running engine is lean compared to 14.7:1 ratio. Or rich.

Sensor cost from $40 up for new. For installation, just weld a threaded 'bung' to your exhaust pipe. It should be at the collector or start of the exhaust pipe, as close to the engine as possible:

How to: welding 02 sensor fitting to exhaust pipe

• $10 a/f sensor from Autospeed article
• full-range LED sensor project from Autospeed article
• datsuns.com tech article.
• For an excellent description with diagrams, download TWM's PDF file www.twminduction.com for their "Halmeter" product.
• Link LambdaLink From New Zealand
• Camden Industries
• Zcar Magazine two excellent articles on using Lambda sensor.
• For more, including build-it yourself A/F meters, see Jason's Weber page

Air Fuel Ratio Sensor

Bosch LSU4.2 sensor was made famous by the aftermarket A/F Gauge companies.

* You can use with dash wideband A/F Gauge
* Haltech can use LSU4.2 with the add-on Haltech CAN wideband kit
* Bosch LSU4.2 5-wire Air Fuel Ratio Sensor (wideband 02 sensor)
* $84 diyautotune.com
* $64 Amazon

But actually LSU4.2 are also used by OEMs like Ford, GM, VW, etc. with various connectors. They are listed as an O2 Sensor with the key words wide band or Air Fuel Ratio. Some examples:

Bosch 17014
* VW Golf 2000-2001 1.8T 
* RockAuto.com $64
* Autozone $64

Denso 234-9002
* 2001-2003 Toyota Tacoma 2WD.2RZ-FE, upstream automatic transmission
* $91 Amazon 
* $108 RockAuto.com

LSU4.2 is already last generation. All OEMs now use the more robust Bosch LSU4.9, but the controller, ECU or gauge needs to support it.