96'NamibianXJ

hi! figured the more places i post the better my chances of advice. anyway, i live in Namibia, Africa and our 96' xj's oxygen sensor is broken and so i was wondering what will happen if i take it out. performance and mpg wise. and if its even possible and how(do i just disconnect it at the wires or is there a plug some place). thank you for any advice, its VERY appreciated.

Bustedback

Replace it, you'll damage the cat converter if you run without the o2 sensors, the mileage will be lousy.

96'NamibianXJ

thanks man. ill try replace it soon. it just sucks that theyre cheap in the States and not here. oh well not the end of the world anyways! whats a CAT converter and whats it do?

nasonguy

the catalytic converter (cat for short) burns off excess exhaust gasses by a catalytic (chemical reaction) process. When you remove the O2 sensor, the engine computer doesn't know what to do, so it makes the motor run really rich (lots of gas). This not only makes for really bad gas milage, but also means that lots of excess, unburned gas will be in the exhaust. When this happens, it tends to "wear out" the catalytic converter a lot quicker than normal.

djb383

Which O2 is broken? USA OBDII ('96 up) XJ's have 2 O2 sensors......1 upstream and 1 down stream of the cat. The upstream O2 (ahead of the cat) definitely effects the way the engine runs....the downstream O2 has no effect on engine performance. Maybe '96 XJ's in Africa still only have 1 O2???????

96'NamibianXJ

i think it has two and theyre prob both broken. is got 160k on it now and as far as i could read up on them they usually last 150k. i know about the upstream one and where its at but wheres the downstream one? is it in the silencer? we took it to the dealer and the said they bypassed the one(i think downstream). so yeah gonna phone them find out how much its gonna cost us tomorrow. like i said if it has two they are probably both gone cause its not functioning properly at all. thanks!

96'NamibianXJ

thanks now i know. that rich fuel mixture sure sounds like our jeep at this present time!! at low revs it feels like theres too much fuel and not enough air in the system and you almost have to keep flooring the gas pedal so it would stay clear or open it seems. very irritating in city traffic. thanks for the advice. we probably should be trying to avoid driving it until its fixed right?

nasonguy

Nope, wrong. Downstream O2 sensor has a huge effect on the system.

The system works by taking the Upsream (pre-cat) readings and comparing them with the Downstream (post-cat) readings to determine what the AF ratio needs to be. It does this in addition to doing a quick analisys with the upstream sensor.

Not trying to be rude or nothin', just fighting mis-information.

In short, if the computer doesn't get readings from the downstream sensor, it can't compare the two, and then doesn't know what the AF ratio should be.
When it can't determine this, it goes in to a kind of "safe mode" or a default fuel map. This fuel map is grossly rich so that no matter what, the motor isn't going to run lean, even at WOT at high altitudes, this is to avoid detonation and bad things like cracked pistons and melted rings.... The only issue with this fuel map is that it is wwwaaayyyy too rich 99% of the time, and that leads to a host of problems...

nasonguy

Should be right after the Catalytic converter, which is just past (towards the rear of the vehicle) the transfer case.

96'NamibianXJ

just found out that the previous owner took out the cat converter and downstream 02! whyyyyy! now what? im thinkin what will happen if we put a freeflow exhaust in? will it be a bit better, or no?

Hommersimpson

if its not against the law there.. yea run 2.5 all the way out the back... get another o2 put in it when you can... it will still run a little rich most likely but wont hurt it....

djb383

Haven't had the downstream O2 in our '98 XJ for a couple of months now. The CEL is on but it's getting mid-teens mpg in-town/city driving and low 20's mpg at 70 mph highway driving......and it runs like a top. Everything I've read says the upstream O2 is the one that closes the "loop" and provides the rich/lean info to the ECU. The downstream O2 just monitors the cat for proper operation.

nasonguy

Interesting, for sure.

When mine was knocked out, I had the CEL of course, but it also idled rough, milage dropped by like 20%, smelled like a volcano when I got on it hard, and it was all sorts of smokey out the tail pipe, haha.

Popped in a new one (I had plain old ripped the old one out on a big A rock, took the plug and everything), reset the computer, every single one of those problems went away.

smtippin

Sorry for hte thread diversion, but on a very related note...I hear a lot of noise about needing to change the O2 sensors together. Is it recommended to change both at the same time? If you're blowing a code for the downstream, wouldn't it be perfectly fine to just replace the one?

s

nasonguy

Common sense tells me that if one wears out, the other is close, so why not just get them both at once?

When I replaced mine, I only did the downstream, but that's because it didn't wear out, I smashed the effer on a huge rock and destroyed it, the front one was untouched, so in theory it wasn't "close" to dying.