View Full Version : B5 S4: Gutting your precats

07-10-2004, 05:49 PM
Gutting your precats

Things needed
- Nice Vise hard mounted with some room to move around it
- Drill with a 3/4 inch Spade Bit (the bits are for wood) and a Metal HoleSaw (I think it was 3/4" but measure the O2 sensor nub to be sure before you drill)
- Hammer and a Punch
- Long large straight Flat Head Screw Driver (that you don't care about damaging)
- Patience, and maybe a few bandaids

- O2 Sensor Nubs (small threaded nubs you weld into the pipe to accept an O2 sensor)
- Pipe Plugs (same thread as O2 sensor to screw into then weld to plug the old hole)

Before removing the Downpipes (DPs), look at where the main cat O2 sensor is. Now pick a spot about 1 inch behind the main cat that you will be able to have the O2 sensor located to with no interference with the body of the car or anything else. Mark the spot with a punch.

Step 1
Remove Downpipes.

Step 2
Clamp one of the pipes into a vise so it is held with the main cat up in the air, so pieces of the pre cat don't fall into it.

Step 3
Use screw driver and hammer, pound the screw driver in between the precat and pipe inner, get it in an inch or so and wiggle it up and down to break the precat away from the inner pipe, keep working around the precat and deeper into it. Eventually it will become kinda loose.

Step 4
Use drill and spade bit to drill into the precat, the chunks will start falling out (make sure you have the main cat up in the air at this point).

Step 5
Keep working with the drill and screw driver till you get it all out.

Step 6
Repeat on other pipe.

Step 7
O2 sensor relocation. The sensor before the precat stays where it is. The sensor infront of the Main cat is the one to move, plug and weld its old location.

Step 8
Drill with the hole saw at the locating you marked before removing the DPs.

Step 9
Weld the new O2 sensor nub into the new hole behind the Main Cat, make sure it is sealed completely around the hole.

Step 10
Repeat on other DP.

Step 11
Reinstall, you will have to untie the sensor wires to get enough slack to move them to the new location, then retie them up.

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