97 Chevy Astro AWD, o2 sensors and catalytic converter

It would take too long to copy and paste all of the picture links individually so for now I'll just put the link to my PhotoBucket pics of the exhaust removal.  If a picture is worth a thousand words, then here's a 34,000 word exhaust removal and reinstallation guide...

http://s715.photobucket.com/albums/ww159/kzoosteve/97%20Astro%20Exhaust/

This was a pretty big job.  I don't recommend it for a rookie but it's not rocket science either.  If you do decide to take this one on, I recommend you use the following tools:

    
1. Plenty of jack stands.  You'll be spending a lot of time under the van, don't take any chances.  I used 4 stands. 

    
2. Eye protection.  Lots of rust and dirt falling off the bottom of the vehicle while your lying on a creeper or on your back lookiing up.  Also required for air tools.

    
3. An air compressor and pneumatic tools are an excelent idea. 3/8 inch might cut it but I used a 1/2 inch gun.  I also needed to use my air chisle/hammer to remove the broken exhaust flange studs. (Not the exhaust manifold flange studs).

    
4. Metric impact sockets.  Deep and regular types, with and without a swivel.  Metric wrenches... probably goes without saying.

    
5. Hearing protection.  You'll be in a tight space with a loud impact wrench near your face.

    
6. A torch.  Not a must, but very nice to have if possible.  I used MAPP gas.  It didn't seem to get the metal hot enough though.  If you can, use oxy-acetylene.

    
7. A saws-all.  If you can't get your hands on one, be ready to use a hack saw to make the cut behind the cat to give you the clearence you need to pull it completely out.

Even after I cut the pipe off just behind the cat itself, I still didn't seem to have enough room to manuver the pipes around to be able to clear the crossmember.  I wound up loosening the crossmember by removing the two bolts on the passenger side and also the two bolts under the transfer case at the rubber mount.  I'm not sure that this was completely necessary.  The thing that really helped was removing the hanger bracket that's bolted to the transfer case.  Two bolts and it's out.

After removal of the exhaust, I first made sure to try to loosen all of the o2 sensors.  As it turned out, I couldn't loosen the one between the cat and the muffler to save my life.  I took the old parts and the replacement cat to a muffler shop to weld the new cat in place and to break loose the one o2 sensor I couldn't get.  As it turned out it took two guys and a torch to break it loose.  It was so tight that it actually stripped the threads on the way out.  The mechanic retapped the threads for me.  My local Lentz Muffler shop charged me $25 bucks for the welding which I felt was pretty reasonable.  After getting the front half of the exhaust back together in my driveway, I'll temporarily duct tape the seam between the cat and the muffler (2nd half) while I drive it out to Lentz to make the second weld.

I recommend that you fit the pipes and cat back into position before you screw in the new o2 sensors.  Don't bolt anything in place, just feed the pipes back in over the crossmember.  Like that you wont risk damaging any of the new sensors durring installation.  You may also want to use some anti-sieze compound around the threads to make removing the sensors easier next time... if there ever is a next time.

A quick note, make sure not to get any solvents of any kind on the sensor side of your new o2 sensors.  I would even use caution not to touch the tip of the sensor with your fingers just to be on the safe side.  Some chemicals can quickly damage the sensors and cause them to give false readings to the onboard computer.

I replaced all four O2 sensors while I had this beast appart.   The total cost of parts was a little over $300.  I figure I saved more than twice that much doing it myself.

Good luck if you decide to have a go at this, and feel free to contact me with any questions.

Thanks,

Steve (01)