For those of you that would like the part numbers for the O2 sensor here they are. Discount Auto is #11039 - Made by Tomco Inc. Description = 3 wire oxygen sensor. Pep Boys #13277. --Jade

That O2 sensor from Discount Auto Parts is EXACTLY the same one I took off the car (the original). It even has the same markings "AC Rochester" & part number on it. This sensor has exactly the same electrical fitting as the OEM one, including the 'slide' where it clips to the car's body. It was $61 vs. the $459 that Lotus wanted. I saved over $400 bucks including taxes. Is this a great web-site or what? --Matthew Welsh

I just installed a replacement O2 Sensor. I used a Bosch #13277. I got it from www.napaonline.com If you go to that site, enter "91 Isuzu Impulse 1.6 Turbo" and then go to the "fuel injection" section and you will see the O2 sensors there (there are more than just the Bosch). I got the Bosch #13277 for $63 plus tax and shipping and I won't go into why I chose the Bosch, but will say it is a perfect fit with a 3 wire lead--it is a direct replacement, but it is not the O.E. part. Upon removal, the O.E. sensor had "AC Spark Plugs", "Made in USA" on its base. The old sensor was completely fouled up and took a bunch of "liquid wrench" and the use of a special O2 Sensor removal socket (similar to a spark plug socket). I can't see the O.E. part number as it was half stripped off by my attempts at removal prior to using the special socket. I'm glad I replaced it though! Put plenty of "anti-seize" on the threads before you install the new one if you ever want to get it out! If you get some other brand please be sure it has the 3 wire lead! --Doug

NGK also lists a compatible Oxygen Sensor (Part# 21012) to the 4XE1-T Isuzu engine on their website

See Charlie's pictures on Oxygen Sensor Replacement here

More info

Oxygen Sensors measure the oxygen content in exhaust gas. Oxygen in exhaust gas accurately indicates how complete the combustion process is. This data is transmitted to the car's ECU in real-time. The ECU then adjusts the air/fuel ratio to keep the exhaust gas in a composition that permits effective treatment by the catalytic converter.

Sensors should be tested at every tune up, and prior to smog checks. In California, 70% of the vehicle smog check failures are a result of poorly operating or failed Oxygen Sensors!!!

Failed and/or poorly operating oxygen sensors can cause a substantial drop in fuel economy. In addition, exhaust emissions can increase dramatically, and poor drivability may also result. Catalytic converters can also fail due to increased emissions.

Fuel additives and injector cleaners that are labeled as "oxygen sensor safe" may be used in sensor equipped vehicles. Use of additives not labeled as "oxygen sensor safe" can damage your oxygen sensor.