Fix It

Depending on what year and what motor you have in your GMC Sonoma will dictate the level of difficulty and the type of catalytic converter you need for replacement. Before the year 2000, the converter was connected to the exhaust system behind the front exhaust pipe in the popular 4.3 liter engine. In the year 2000, the catalytic converter became the front exhaust pipe which is much more challenging and difficult to remove and replace.

Instructions

How to Install a Catalytic Converter in a GMC Sonoma

1

Lift the GMC Sonoma all the up on the car lift. Load all the tools and the new converter into the tool cart/tray and wheel it over near you under the Sonoma, but out of your way. Put on the safety glasses.

2

Locate and remove the oxygen sensors. In the front Y-pipe converter application, there will be three oxygen sensors. In the older kind of Sonoma, there is only one oxygen sensor. Locate the plugs for the wire and unplug them using the flathead screwdriver to press in on the clip lock. Use the ratchet and oxygen sensor socket to remove the sensors. If need be, you may have to heat the pipe up a little with the torch to extract them. Allow them to cool down if you needed the torch.

3

Screw the oxygen sensor(s) into the new converter, but apply a light coat of anti-seize lubricant on the threads first. For the Y-pipe with three sensors, make sure to put the correct sensor into the correct port. Be caul not to overtighten to prevent stripping out the threads of the sensor(s).

4

Light the torch with the striker and heat up one nut on the manifold stud at a time (for the front Y-pipe converter). When the nut is cherry red, place the pneumatic gun, extension, swivel and socket onto it and remove the nut. If the converter is connected to the front pipe, cut the three nuts and bolts with the torch on both sides of the flange, then use the hammer and punch to knock the rest of the bolt out of the flange connection.

5

Cut the two or three nuts and bolts out of the rear flange connection on the converter using the torch. Cut the bolt on both sides of the flange and knock the rest of the bolt from the flange connection using the hammer and a punch. Be caul on the last bolt as the converter will separate from the exhaust system. Put on the gloves and remove the old converter.

6

Install the new catalytic converter starting with the inlet first (closest to the motor). Install the gasket(s) first and then thread on new manifold stud bolts for the Y-pipe converter or replace the nuts and bolts on the converter connected to the front pipe. Use a bolt head and washer on one side and a lock washer and nut on the other side of the flange.

7

Tighten the nuts on the manifold with the gun or tighten the nuts and bolts on the flange connection, using the gun on one side and holding the bolt steady with a hand wrench on the other.

8

Replace the gasket and hardware on the rear connection of the catalytic converter. Place the bolt head and flat washer on one side and the lock washer and nut on the other side of the flange connection. Tighten with the gun on the nut side and hold the bolt head with a hand wrench.

9

Plug the oxygen sensor wire(s) back into the plug(s).

10

Remove the tool cart and any other debris from under the Sonoma, lower the truck and start the engine up. Raise it back up and check for any possible exhaust leaks coming from the manifold, flange or oxygen sensor connections. Tighten as needed.

The 4.3-liter six-cylinder engine in your 2002 GMC Sonoma is equipped with many ways to reduce the harmful emissions created from the combustion process, and the most effective way is through the use of the catalytic converter. When the converter becomes clogged, you will likely experience a drop in fuel economy and engine performance. Your converter is located under the passenger compartment and connects between the exhaust manifold and the muffler inlet pipe. To remove the converter assembly, the rear transmission support will have to be removed.

Instructions

Removal

1

Park the truck on a level surface and set the parking brake. Lift the front of the truck into the air with the floor jack and place two of the jack stands under the front frame rails. Lower the jack until the truck rests securely on the jack stands. Remove the floor jack.

2

Place a block of wood on the jack arm and raise the jack until the wood contacts the transmission pan. Pry up on the transmission wiring harness plastic retainer on the transmission support to remove it. Remove the transmission mount to support stud with the socket and ratchet.

3

Place the third jack stand under the converter assembly and raise the stand arm until it is high enough to support the assembly. Remove the bolts for both of the converter hanger brackets with the socket and ratchet. Remove the three bolts securing the transmission support to the frame rails with the socket and ratchet. Remove the transmission support, washers and reinforcement from under the vehicle.

4

Disconnect the truck wiring harness from the right and left pre-cat oxygen sensors and the post-cat oxygen sensor by squeezing the tabs and pulling them apart. Remove the two converter assembly to muffler pipe nuts with the socket and ratchet. Remove the three flange nuts for the right and left manifold to converter assembly mounting studs.

5

Support the converter assembly by hand and remove the jack stands. Lower the converter assembly and slide it out from under the truck. Pry the both of the rubber hanger and brackets from the converter assembly.

6

Mark each of the oxygen sensors with tape so they can be installed to the same location during the installation process. Place the oxygen sensor socket over the left pre-cat oxygen sensor, making sure the pigtail sticks through the slotted portion of the socket. Remove the oxygen sensor with the oxygen sensor socket and ratchet. Repeat for the right pre-cat and post-cat oxygen sensors and set the oxygen sensors aside.

Installation

7

Clean the oxygen sensor threads with a wire brush. Install a small amount of copper anti-seize to the threads of the oxygen sensors. Install the oxygen sensors to their respective fittings on the converter assembly and tighten to 31 foot-pounds with the oxygen sensor socket and torque wrench. Push the rubber hanger over the hanger arm on the converter assembly; allow the bracket to hang.

8

Install the new exhaust gaskets onto the muffler pipe and both exhaust manifold. Slide the converter assembly under the vehicle and position it under its mounting location. Place the jack stand under the truck and lift the converter assembly onto the stand. Balance the converter and guide the outlet end onto the muffler pipe studs. Install the retaining nuts hand tight.

9

Support the opposite end of the converter assembly by hand and remove the jack stand. Guide the converter assembly inlet onto both of the exhaust manifolds and install the mounting nuts hand tight. Tighten the exhaust manifold nuts alternately to 30 foot-pounds

10

Connect all three oxygen sensor pigtails to their respective wire harness plugs. Set out the transmission support bolts and place a washer on each one. Set the transmission support into place and hold the reinforcement plate in position on the frame. Slide the mounting bolts through the frame and hold them in place. Install a washer to the over each mounting bolts and tighten the nuts to 40 foot-pounds.

11

Install the transmission mount nut and tighten to 42 foot-pounds. Swing the converter hanger bracket up and hold It to the transmission support Install the bracket mounting bolts and tighten to 13 foot-pounds.

12

Lower the floor jack and remove it from under the transmission. Push the transmission harness retainer into its mounting hole on the transmission support. Lift the front of the truck off of the jack stands with the floor jack and remove the jack stands from under the truck. Lower the truck to the ground and remove the floor jack.