Trying to get better mpg, I bought the two bosch O2 sensors to replace them in my WJ 99 4.0. Last weekend, I prepared all the stuff. The downstream was very easy, but the upstream, was very hard to unplug the wire. About 20 minutes later, I did it, but when I took the new bosch sensor to screw it, big suprise.
I can't put it in the hole of the mud because it's larger than the OEM and it hits the transmision box. I tried for 2 hours to install it but I can't.
Finally, I reinstall the OEM again.
Does anybody knows what is the way to replace it ?
What can I do ? Thanks for any help.

Do the two replacement Bosch's have the same part #? Upstream & downstream are two different part #'s. . hence a possible clearance issue @ the upper end?