I have been reading around alot and most threads talk about the O2 Sensor before the cat and after..

So here is my question..

I have an 02 Sensor right after the y pipe.. then.. down about 1 FT~1.5FT away from the rear axel.. is the Cat.. O2 Sensor sits in front about 6 inches up stream on the pipe.. nothing on the other side of cat.. cat is about .75ft away from muffler.. all looks stock..

Any idea?

Also.. will I have a problem once the Cat goes 'missing' and a pipe is placed there instead?

 

I have a Sport and it has one pre-cat and one post-cat, post cat is between the muffler and the rear axle. I know mine is factory because I bought it new. Can't comment on your set up, sorry.

 

I have an '01 Dak Sport 4X4, 4.7l, auto, with California emissions

Precats on both cylinder banks feed into a Y pipe, then into a cat right before the muffler. Mine has 4 O2's, one before and one behind each precat.

Sounds like you have a Federal emissions truck. Single cat before the muffler with two sensors, one fore and one aft of the cat. From what I've read here and elsewhere you can add a 'simulator' to the rear one (to keep the CEL out) and ditch the cat, but you need the front one in place and working to control fuel/air ratio.

Hope this helps

Have a good day

David and the Mutts

 

Yeah everything looks 100% factory.. 1 sensor after the y pipe and one right before the Cat.. nothing after.. weird..

 

Anyone know when those cat sensors need replaced? I'm over 95k on my truck.

 

Just replaced mine @ 94,000. Recommended @ 100,000 I believe.

 

Bump?...

 

From: http://www.thepartsbin.com/oxygen-sensor.html


Know When to Replace Your Oxygen Sensor

Here are some fast and reliable diagnostic procedures which you can use to check out most oxygen sensors. A great time to do his is when you are performing a tune-up. The following symptoms will help tip you off to a failed oxygen sensor: Surging and/or hesitation
Poor or a decline in fuel econmy
Failed exhaust emissions testing
Premature failure of the catalytic converter (rotten egg smell)
Indicator "idiot" check engine lights coming on
Replacement Intervals Replace unheated oxygen sensors on 1976 to early 1990s vehicles every 30,000 - 50,000 miles Heated (1st generation) oxygen sensors on mid-1980s to mid-1990s vehicles every 60,000 miles Heated (2nd generation) oxygen sensors on mid-1990s and newer vehicles every 100,000 miles. Keeping the OEM oxygen sensor fresh may improve fuel economy as much as 10%-15% (which can save $100 each year in fuel costs on average). Keeping the sensor in good operating condition will also minimize exhaust emissions, reduce the risk of costly damage to the catalytic converter and ensure peak engine performance (no surging or hesitating). For these reasons, the oxygen sensor should be considered a "tune-up" replacement item just like spark plugs, especially on older vehicles (those built before the mid-1990s). Tips to Remember Follow these steps and you're well on your way to passing emissions with flying colors and saving money in fuel costs & repair bills: #1: Increased fuel consumption, engine problems (hesitation or surging), "Check Engine Light" lit or emissions test failure could all be signs of an oxygen sensor in need of replacement. #2: Checking the operation of the oxygen sensor and feedback control system should always be a priority anytime a vehicle fails an emissions test due to high HC or CO.


End Quote......

But the sell parts..........FWIW

 

O2 sensors typically last 80k miles. After that they tend to slow down or die altogether. Normally they fluctuate about 0.5V between 0.1V and 1V twice per second in a sine wave pattern, usually like 0.3V to 0.8V. When they get old they tend to slow down like an older person on a walker. They may still fluctuate but maybe every say, 5 seconds. The ECU is expecting twice per second, so when this happens it thinks the sensor is stuck and you get CELs with codes like "O2 sensor stuck high" (or low) or "out of range" or something like that.

Your fuel mileage will probably be affected because the ECU relies on the O2 sensor's signals to determine the fuel mapping to use. "Bad" signals will result in bad mapping and possibly "safe" mapping (fuel dumping to prevent overheating from a perceived lean condition) with the ECU disregarding the O2 sensors completely and your fuel efficiency will suffer.

 

so, i have 210000 on my stock sensors all 4 of them. i think i will be in a world of hurting soon. and i have over 100k miles on my spark plugs. i am suprized it is still running. 10-15% gain in fuel econ. is what you say i could get with new O2 sensers? i may need to put in some new ones.