Downstream o2 sensor question....

[huntingfinatic]

Hi all... 99 cherokee classic 179,xxx -my mileage has dropped considerably(from 18-20 to 10-12) the past few months. No real changes to driving habits, speed, traffic...... and so on. CEL came on several times.... went to parts store.... OBD II says downstream voltage (blah Blah). Reset it.... week or two later... light on again. Same thing. Scan, reset order front and rear sensor. Ordered front one too because its my understanding that that is the one that varies fuel mixture. (rock auto cheaper for both shipped to my door than O'reilly was for one). Anyways, 20 mins and sore hand from strippin the threads out of the bung to remove the rear sensor...I have no threads to screw the new sensor into. My thought is to rough up the old bung, go to exhaust shop in morning, get a new bung i can weld on right on top of the old bung. It should still heat up like normal, but may be out of the " "stream of exhaust a bit. Any thoughts or suggestions on whether that will mess with the signal to the ECM?

[Mudderoy]

Hi all... 99 cherokee classic 179,xxx -my mileage has dropped considerably(from 18-20 to 10-12) the past few months. No real changes to driving habits, speed, traffic...... and so on. CEL came on several times.... went to parts store.... OBD II says downstream voltage (blah Blah). Reset it.... week or two later... light on again. Same thing. Scan, reset order front and rear sensor. Ordered front one too because its my understanding that that is the one that varies fuel mixture. (rock auto cheaper for both shipped to my door than O'reilly was for one). Anyways, 20 mins and sore hand from strippin the threads out of the bung to remove the rear sensor...I have no threads to screw the new sensor into. My thought is to rough up the old bung, go to exhaust shop in morning, get a new bung i can weld on right on top of the old bung. It should still heat up like normal, but may be out of the " "stream of exhaust a bit. Any thoughts or suggestions on whether that will mess with the signal to the ECM?

I know the front O2 sensor has to be inside the exhaust tube a certain depth. I suspect the rear is the same way. So you would need to get the new bung at the same depth.

[DeftwillP]

Get a new high flow cat off of eBay. Win win.


Tapatalky

[OrangeXJ]

You may be able salvage it by running a thread chaser through it. It should be 18mm

[4.3LXJ]

You might check into getting it heli coiled too. You would have to pull the pipe for that, but shouldn't be too big of a deal. If you pull it to weld it anyway, you can also weld up the old hole, drill a new one and weld that bung in in a little different position. Orientation does not matter.

[bigjim350]

Having the downstream O2 a little further out of the exhaust flow won't hurt anything. The only difference might be that your ECM thinks its running a little cleaner than it really is.

[huntingfinatic]

Well fella's I called a local muffler shop. Bought a new bung for $5. 4 1/2" grinder and cut off wheel made short work of the old bung, two mins later had the new bung welded in place. Didn't have to take off cat or driveshaft or nothing. I did have to borrow my wifes compact mirror out of her purse in order to see the top side of my weld. I had to use the force to do that side. Couple little squirts to fill the potential pinholes where i couldn't see my puddle. Hopefully this will cure my issue. New cat will be next process. I did a tune up with plugs, wires, air filter ect. already. Just think it may not be breathing well enough. Thanks for the input all!

[Mudderoy]

Well fella's I called a local muffler shop. Bought a new bung for $5. 4 1/2" grinder and cut off wheel made short work of the old bung, two mins later had the new bung welded in place. Didn't have to take off cat or driveshaft or nothing. I did have to borrow my wifes compact mirror out of her purse in order to see the top side of my weld. I had to use the force to do that side. Couple little squirts to fill the potential pinholes where i couldn't see my puddle. Hopefully this will cure my issue. New cat will be next process. I did a tune up with plugs, wires, air filter ect. already. Just think it may not be breathing well enough. Thanks for the input all!

I'm glad you did it this way. This has to be the best way to do it.

[LizardRunner]

Sounds like a good fix to me. The muffler shop I use said they would do the bung replace for 15.00 total it was up to me to pull and replace the sensor though.

[huntingfinatic]

Here are my results....seems it made a substantial difference. back to that 17-18 mpg area. I took it on a longer drive (220 miles non city driving) 65-70 mph. Not bad for wintery, snow covered roads and a little spinny spinny here and there for the first 100 miles of it.