Front/Upstream O2 Sensor Replacement Problems

[dimwittedmoose51]

Have a99' VE with 156k on it and I'm replacing the original O2 sensor with the flat flange on the exhaust manifold. Got both heat shields off and used enough PB Blaster to get the 2 12mm nuts off with no problems. Now, I'm at a standstill as the flange on the O2 Sensor is butting up against the Driver's side Spring/Bolt that holds the tails pipe to the exhaust manifold.

1. If I try to tighten the bolt/spring combo to move it up further and allow access so the flange can clear, I'm not sure how to do that. Access to the 14mm bolt head is near impossible from under the car and trying to tighten or loosen it from above is just about impossible, especially if I try and get any sort of torque on it. I did buff the exposed threads with a Dremel wire brush before I PB Blastered it, but still have the clearance issues to deal with.

2. If I try and remove the front stud by double nutting it , that would drop the flange enough so I could remove the old one, but I would be pushing my luck with rusted studs/nuts.

3. My only other option is to try and grind enough off the top of the exhaust manifold spring/bolt so as to get clearance that way

None of these possibilities is a good one, so does anyone on the list have a better idea?? Haynes was no help at all......

Thanks,

DM&FS

[dimwittedmoose51]

Plan #4 might be to take the Sawzall or die grinder and cut the flange on one side so the old unit could be removed and then notch the new one for clearance. We're talking an 1/8 of an inch here max.

[dimwittedmoose51]

Sawzall wouldn't fit, Makita 4" grinder was too scary to use under there in tight quarters, and double nutting the forward stud was useless. That left grinding with the Dremel and the1/8" carbide router bit available at most hardware stores. I used the one with the rounded end. Slow going for sure,as that flange is made of real high quality stainless steel and the rear bolt hole areas were attacked first. Took my time and the upper and lower cuts done and it still wouldn't clear the exhaust bolt head. Success finally came when I stuck the Dremel and the carbide bit in between the interfering surfaces.

After maybe each 60 seconds of grinding, I'd pull out the tool and see if the old sensor flange would clear. At this point, I didn't care if the metal came off the bolt head or the O2 Flange. Maybe 3 rounds on each side did the trick and it finally came out, although I never did get the router bit to pass completely through the congested area. At that point, I didn't care. I just wanted to move forward. It's really difficult seeing what you're doing in there as well and maybe having a small mirror would be helpful too. I was careful not to nick the studs or the gasket surface.

I still haven't figured out how you are supposed to remove the exhaust pipe assembly with the O2 sensor in place. I did grind a bit off the new Denso sensor flange top edge so I won't have this issue in the future. Even with the O2 sensor off, it's certainly a tight fit under there for that driver's side exhaust bolt. Definitely a place where a 3/8" pnuematic 90 degree air wrench would come in real handy.

Hope this will help someone in the future....

DM&FS