Originally Posted by snakedoc67
Looking at picking up an O2 sensor from a JY cherokee for my Comanche since I cant afford a new one at this time. Have looked thru the posts the last few days here and on ComancheClub but have not seen any way of testing to see if its any good. Any ideas for a test for the O2 sensor and what has been the experiences with a sensor from the jy? http://www.jeepforum.com/forum/images/smilies/dunno.gif
With the engine off and sensor unpowered, you can test the heating element - but that does nothing to measure the actual effectiveness of the sensor proper.
You'd need to run the engine and use backprobe pins on an analogue meter or an oscilloscope to read the sensor switching - and that won't happen at a breaker's.
A HEGO is something I would flatly refuse to buy from a breaker's. Yes, you may get a useful one, but you won't know how much life it has left in it - and it's at least as likely you'll get one that won't work worth a crap.
My advice? Start saving your nickels, and plan to buy a new replacement. They're less than $100 for a "direct fit" replacement, you may as well do it right the first time (save yourself the work, save the money for having to buy it twice - and a failed HEGO from the breaker's will be effectively the same as what you're dealing with now - the ECU will "swing rich" if the signal from the HEGO is bunk, to prevent engine damage (13.2-13.5:1, usually. Rich enough to prevent detonation, but not so rich as to cause washdown.)
Leave it be, save your money to do it right the first time. It's an MJ, so it will be RENIX or OBD-I (depending on year,) and neither is horribly picky about the HEGO RENIX can ignore it readily, and OBD-I will eventually throw a code - which can be cleared when you replace the sensor with a new part.