My truck is a Cali emissions truck and is still on the original sensors and my truck has gotten a bit stinky from the tailpipe on startup and it has a shudder (not misfire) that settles about 30 seconds after startup and wondering if either of the sensors has gone bad but not throwing a CEL.
I did a search but it's alot wading thru all that info trying to find what I want.
Do I need to replace both sensors or just replace the rear one first?
And what's the Denso part # and where the cheapest I can find it?
My MPGs have been under 15mpg but a short 1 mile round trip commute isn't helping.
Your Cali emissions model uses an air/fuel ratio sensor precat vs. the normal ol' oxygen sensor that was on the federal models.
Pretty common for the Air/Fuel ratio sensor on Cali emissions models to fail resulting in high carbon monoxide levels, poor running, and fuel economy without setting a trouble code.
They are a bit more difficult to accurately test on the ol' 3rd gens but here are the steps if you wish to diagnose further:
1. Check the rear Oxygen (O2) sensor voltage. See if it is reading high voltage above 0.6 volts indicating rich, or if it is reading low voltage below 0.4 volts indicating lean.
2. If the rear O2 sensor voltage reads low, check for exhaust leaks.
3. Add supplemental fuel and see if the fuel trims go negative and if the rear O2 sensor voltage jumps high.
4. If adding supplemental fuel raises the rear O2 sensor voltage, but the fuel trims remain high positive, it could indicate the A/F ratio sensor is not reading correctly.
5. Unplug the front A/F ratio sensor and check for 3.3 volts and 3.0 volts on the White wire and the Black wire at the A/F ratio sensor harness side connector with the key on.
6. With the A/F ratio sensor unplugged, see how the engine runs and how the fuel trims respond and if the CO comes down.
the part can be found here.
http://www.amazon.com/Denso-234-900...sr=8-1&keywords=4runner+air/fuel+ratio+sensor
