I just went through this ordeal, so I thought I'd share some tips.
I won't cover what the CPS does, or how to diagnose it. Once you've determined you need to change it, here are some strong "hints".
1. It's located on the back of the block. On an 89 3.1 I was able to crawl under and work on it from the bottom. Find a two-wire connector. Connector is set at a 90 degree angle to the block.
2. After Unplugging connector and moving it well out of the way, you need to soak where the sensor meets the block (all the way around) with some type of cleaner or penetrant. The advise I got was CARB cleaner, because there is coking from the engine that needs to be broken down. I used Berryman's and it helped. NOTE that carb cleaners can be VERY toxic! Where it touched my hands, my hands were burning. Wear gloves, eye, nose/mouth protection. Actually I didn't even spray the stuff directly. I took a cotton ball, soaked it in the cleaner, and then patted around the area.
If you have the luxury of time, I recommend you soak, wait a day, soak again.
3. When you go to pull the sensor, be gentle. The plastic will be very brittle from the years. Try to pull straight out when you are pulling. Occasionally twisting it (but never side to side) will help. You may have to resort to using a screwdriver to pry. If so, try to use a very wide screwdriver, and better yet put one on each side of the sensor and work them together. If you hear cracking, in my opinion, stop and soak it some more.
4. If it breaks (and it did for me), and you don't have anything you can grab with pliers or it broke too deep to insert pliers, the advice given me was to take a metal pick or a drywall screw and heat it up red-hot with a torch, then poke into the plastic sensor. Allow to harden and cool, then pull out. NEVER do this with carb cleaner or other solvents in the area, wait till those have completely dried. I chose a drywall screw about 2.5" in length, locked into vice grip pliers. I had a helper heat the screw red hot (stuck my arm out from under the car), and then I gently but with some pressure pressed into the sensor. Wait two minutes, and pull. Repeat over and over and it comes out.
Yes there are other possibilities (pushing it out from the inside if you've dropped the oil pan, or pushing it into the block and then leaving it or taking off the pan to get it out) but I believe this is the fastest way.
Hope this helps someone!
Thursday, September 29th, 2011 AT 1:10 AM