Saab 9000 Catalytic Converter Heat Shield Fix

Just finished this and thought I'd post it up as a reference for others. My main symptom was a rattle between 1000-1500rpm that sounded like bolts in a pan being shaken around. Closer inspection revealed it to be the heat shield on top of the cat that was rattling against the cat itself. The welds holding the two together had corroded through...permissible as the car has covered 160,000miles. An easy way to confirm this before spending much time/money is to wedge a coil of copper wire between the cat and heat shield and see of that stops the rattling. If so, the heat shield is the culprit. Once you've confirmed it's the heat shield you can set about removing the cat.

Tools you'll need

Axle stands, trolley jack, 13mm ring spanner, 16mm ring spanner, copper grease, lambda sensor spanner (adjustable wrench will do), welding kit/friend who can weld for you.

Optional but highly reccomended

Turbo to downpipe stud and bolt kit (3 x studs and 3 x 13mm nuts), 13mm locknuts for exhaust flanges as the old ones have a habit of rounding off.

Step 1

On safe level ground get the front of the car up on axle stands. You can remove the road wheels if you like but I found they didn't get in the way

Step 2

Under the bonnet unplug the lambda sensor from the wiring loom and remove the connector from it's bracket at the base of the oil dipstick tube. Remove the clips holding the lambda sensor wiring to the metal hose running down the side of the engine next to the aux belt. Loosen the 10mm nut holding the lambda sensor wire clamp at the bottom edge of the AC compressor mounting bracket. These steps should give you enough freedom in the wiring to unbolt the sensor itself without damaging anything. If quite old the sensor itself may be difficult to unbolt - give it time, patience and plenty of WD40. Once removed place it into a jiffy bag or similar to protect it from dirt/oil/knocks.

Step 3

Next, loosen the three 13mm nuts holding the exhaust downpipe to the turbo. Plenty of WD40 and heat will probably be needed unless you've been here recently. A very short 13mm ring spanner would be useful for the bolt furthest from you as it's nestled under the exhaust manifold and difficult to get enough 'angle' on it with a longer spanner. At this point some of the studs may decide to come out along with the nuts. It may be an excellent time to replace the studs and nuts for piece of mind/ease of re-assembley. If you plan to re-use your studs and nuts make sure you clean up the threads and get any studs that have come out all the way back into the turbo before you re-tighten the nut.

Step 4

Time to get under the car. Place the trolley jack under the cat with a piece of wood between the two for protection. Make sure the jack is high enough to take the weight of the cat. Now loosen off the two 13mm nuts holding the mid-section and flexi-section of the exhaust together. This is advisable as the union between the cat and flexi is likely to be a much tougher job and you're much more likely to encounter rounded nuts and other rusty bolt related headaches.

Step 5

With the downpipe loosened and the flexi/mid exhaust section separated, all that holds the cat onto the car is one 16mm bolt on it's topside. With the jack taking the weight loosen said 16mm bolt and then gently lower the section of exhaust from the car using the trolley jack. The downpipe may need some assistance to help thread it out of the engine bay.

Step 6

With the cat off the car you can inspect the damage. I found that the two welds next to each other at the one end had rusted through and the shield itself was left wobbling around in the air connected by just one weld at the other end. My fix was to get a friend to re-weld these joints and re-enforce the one weld that haddn't rusted through. Here's a pic of the cat after welding:

Step 7

Once you've re-welded the heat-shield you can fit the chunk of exhaust back to the car. In true Haynes style, the fitting is the reverse of removal. The only things I'd point out are to make sure the exhaust unions are all well-fitted and make sure you use new exhaust flange nuts if in any doubt about the condition (read: how rounded they are!) of your current ones. Pop some copper grease on the lambda sensor when you re-fit to ease future removal.

Hope this helps anyone who's got the same problem.