how many oxygen sensors???

hrjaw · 12-13-2004, 07:54 AM

Good Morning All,
I am looking to replace the O2Sensors in my 99 wj 4.0....my jeep has hit 90,000 miles and my gas mileage has dropped quite a bit recently.....all the routine maintenance has been done....my question is this...my local dealership states that i ahve california emissions, which means that i should have 4 sensors....the two downstream sensors which i have, and they sold me one upstream sensor...however....they state that i only have one upstream, not 2....can anyone clarify this for me???......it would be cheaper to replace three vs 4, but if i need 4 then i will replace all 4....

Meerkat · 12-13-2004, 08:31 AM

Here ya go...

**Texas ZJ1** · 12-13-2004, 09:08 AM

I understand the confusion.

IN some repair books, some V8 ZJs have two O2 sensors. Yet, the year models do make a difference. The V8s prior to 96 have one. Post 96 have two.

Hunter

hrjaw · 12-13-2004, 09:51 AM

thanks for the quick response everyone......one last question...does anyone have the part # for these so that when i go back i can get the right ones?
thanks again,
Roger

WVZJ · 12-13-2004, 11:59 AM

I strongly recommend you get the mopar sensors. They last longer than your average sensor and they plug into to your harness, you won't have to splice any wires.

hrjaw · 12-13-2004, 12:06 PM

well, that is the problem. that is what i was trying to do. i went to my jeep dealer to get the o2 sensors, and i have three so far...two downstream, and the one upstream. it's the second upstream that they seem to have a hard time finding for me. i even gave them the vin # and all, and they don't know which additional sensor it is i need to buy. the crappy part is that once i buy it, i can't take it back, even if it was sold to me wrongly.

Meerkat · 12-13-2004, 12:08 PM

Instead of having one large catalytic converter after the 'Y' pipe, 99 and newer California models have two small catalytic converters in the 'Y' pipe. That is why they have four O2 sensors, one before each cat, and one after each cat, but before the 'Y' merges into a single pipe.

HTH

Meerkat · 12-13-2004, 12:12 PM

Oops, I just realized you only have a 4.0....
you should only have two O2 sensors, one before the cat, and one after....

**Texas ZJ1** · 12-13-2004, 12:16 PM

OM,

did Warren goof?

Hunter

Meerkat · 12-13-2004, 12:18 PM

**Phil Gerard** · 12-13-2004, 12:44 PM

Quote:

Originally Posted by Texas ZJ1

OM,

did Warren goof?

Hunter

No, he was just workin with limited data!!!!

Phil

hrjaw · 12-13-2004, 12:59 PM

i thought i should only have one up and one down also, but my california emissions vehicle does seem to have 4 sensors. two up and two down.
Roger

Meerkat · 12-13-2004, 01:05 PM

What would be the point?
As you'll notice in the picture I posted earlier, it shows 4 sensors, but that is two per catalytic converter. One converter is mounted on each leg of the exhaust manifold. Since it is a V8 in the picture, it has two legs. A six cylinder is only going to have one pipe from the exhaust manifold to the muffler.
It has occured to me that it may have 4 for redundancy so California doesn't get smogged up if an O2 sensor fails, but I rather doubt it.
There is only one way to resolve this issue... you are going to have to actually count the converters.
Something else to keep in mind. The downstream O2 sensor is not going to affect your gas mileage. So if it comes down to it, make sure the upstream one or two sensors get changed first. Then take care of downstream if need be.

HTH

hrjaw · 12-13-2004, 03:10 PM

Warren,
i just went out and checked. it does indeed have the two individual dog legs/pre cats...i.e. California emissions. so that would lead me to believe i do indeed have the 4 sensors. i am going to try and order the two upstream, but the dealer wants the part # of off the old sensors before they will sell me the new one. this should be fun!
Roger

Meerkat · 12-13-2004, 03:33 PM

Well, I am nonplussed...

I knew the newer 4.0's actually have split the exhaust manifold to it is more like two 3 cylinder exhaust manifolds on the same side, but I figured they would go to a common collector. That's quite amazing.

I think I would have to try to find a different dealer though. They should be able to look up the number for your O2 sensors themselves. Additionally, they should have been able to (correctly) tell you how many sensors there are and where they are located.