Friday, May 24, 2013

The Brick Chronicles: Catalytic Converter/Exhaust Manifold (?) Phase II

Last time, in the Brick Chronicles, I had just ordered a catalytic converter. Since then, I've gotten to work on Phase II: Installation. With most people clearing out after graduation, I had a nice shady corner of the parking lot to myself. After all, I guess I am now a "shady tree mechanic."

Ad-hoc parking lot garage setup.
The jack setup in the picture above is rated at 9 tons (safety factor of about 6!). Anyways, the cat is split from the pipe that once connected it to the muffler, so the first step was to remove the section that was severed and not perturb the muffler pipe. The interface is this rusty two-piece bracket, which as far as I could tell was kept together by the remnants of some kind of pin. I pried the bracket apart using a flat head screw driver and some pliers. I honestly believe this is the procedure Volvo intended because if you're changing the cat then it follows that your hardware is ~15 years old.  

Rusty bracket.
Removing the brackets revealed the rusty pipe interface. I was a little concerned that this connection was welded at first. However, after blasting it with penetrating oil and torquing the free pipe with adjustable wrenches in opposite directions, it twisted right off. 

Rusty tubes.
Ta da.
Enter, the stubborn oxygen sensor.
With the pipe free, I could now access the downstream oxygen sensor. It makes most sense to remove the entire assembly before extracting the sensor because the pipe is free and unwieldy to secure. Before removing the pipe, a skid plate is blocking the sensor wire and must be removed.

The wire is held to the frame via a series of clips which I pried up with a flat head screw driver. I did not have a good means of fixing the pipe in place in my parking space garage so I actually ended up following the wire up to the wiring harness in the engine bay, and removing the whole thing from the car. Remove the air distribution hose from the filter housing to access the wiring harness.

The silver washing machine hose like thing is the air distribution hose.
The left connection goes to the front sensor, and the right goes to the rear. There are red clips that you can pry up. At this point - poking around with a screwdriver in the engine bay - it would have been wise to start doing things one-handed because the chassis is live (floating ground). I elected to take off my watch and try not to touch things.

Oxygen sensor connectors.
One piece.
Moving on the oxygen sensor extraction, I'll start by saying how you shouldn't do this. I tried to take a shortcut and extract it while the wire was still tethered to the car; with the available slack, the assembly reaches just a few inches outside of the frame. I'm not proud of this, but my plan was to wedge one end of the pipe under my front tire and get a foot on the other end while wrenching on the sensor. Attempt one involved a liberal dose of penetrating oil (probably five coats all told) but was not enough to sufficiently break through the fillet of rust fusing the sensor to the pipe. No dice. For attempt two I lit a small fire (I hope nobody from DOTS reads this) and roasted the threaded part of the tube, attempting to expand it and release compressive stress on the threads. Still nothing. A third method involved melting candle wax into the threads to lubricate them. This failed because rust almost entirely concealed any access to the threads, and was admittedly only attempted because I read about this trick online and how cool would that have been if it worked? All of these attempts were useless because my method of constraining the pipe with tire and foot was JV at best.

Once I finally detethered the pipe/sensor assembly the sensor came right out with the help of a vice and a big wrench with a pipe to make it even bigger.

A more sensible strategy.
So, that's half of the cat removed and one oxygen sensor (of questionable functionality) salvaged. I am optimistic that the sensor still works and am reading into ways to diagnose this without a legit OBDII scanner (i.e. using an oscilloscope). We'll slate this as a problem for future self. Next up, I will remove the upstream oxygen sensor and the larger part of the cat, which is buried deep in the engine bay. Here's the updated scoreboard:

D.E.C. catalytic converter - $396.55 (FREE SHIPPING!)
+        Exhaust flange gasket - $3.95
+     Oxygen Sensor Socket - $17.00
=                                         $416.50
($2000 - 416.50 = 1583.50)

In the green for now at least. You can borrow oxygen sensor sockets from Autozone free but I figured this was an investment for future brick chronicles and car repair projects. Until next time.

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