EXHAUST TECH:

Replacing catalytic converters and a muffler

by Marc Olivares

PREFACE:

My 1999 Discovery recently logged a P0420 code for catalyst inefficiency. Since I routinely used my catalytic converters as rock sliders, I knew this would be an inevitable repair. What I hadn't anticipated was the outrageous cost for a replacement Y-pipe. As I researched, I found that a new Y-pipe ranged in price from the mid 500's to over a $1000. Since my beloved Discovery is getting on in age, I couldn't see spending over $1000 on exhaust work, so, I began exploring the option of universal weld-in converters.

CATALYTIC CONVERTER OPTIONS:

The Land Rover Discovery series 1 came with a Y-pipe that has roughly a 2-1/8th outer pipe diameter. If the method described below is used, the selected converter must have meet the following criteria:

  1. Have a minimum of a 5500 lb rating
  2. 3-way converter style
  3. 2-1/4" inlet and outlet
  4. Width between 4" and 4-1/2"
  5. Height between 6" and 6-1/2"
  6. Overall length between 13" and 16"

The following are a few examples of converters that will work on a Land Rover 4.0L v-8:

MY CONVERTER AND MUFFLER SELECTION:

For simplicity sake, I chose the universal OE replacement converter by Maremont. These converters can be found at any affiliated CSK parts store around the country. Mine came from a Checker Auto Parts. When purchasing a Maremont converter, the reference book lists the replacement converter as part number 38502. This converter will not work for installation method I describe below, due to a 2" inlet/outlet inner diameter. The 38503 is the same converter as the 38502 with a slightly larger inlet/outlet inner diameter of 2-1/4".

The muffler I selected is also a Maremont OE replacement part that is designed for a 1993-2003 Grand Cherokee. This muffler (part #103192) is approximately 2" longer and 2" narrower than the Land Rover OEM part. This muffler has a center inlet and an offset outlet, both having inner diameters of 2-1/4"s.

PARTS NEEDED:

TOOLS NEEDED:

PART 1: CATALYTIC CONVERTER INSTALLATION

To remove converter from the vehicle, you much first disconnect the (4) oxygen sensor connectors, remove the (6) 13mm nuts from studs on exhaust manifolds, and lastly remove the (2) nuts from the Y-pipe/muffler flange.

Once removed from the vehicle, give the Y-pipe a visual inspection, check for cracks or deterioration on the pipe and flanges. The converter on the driver's side of my Discovery had suffered mild rock contact and was likely the reason for the premature catalyst failure. Next, remove the (4) oxygen sensors using a 17mm flare nut wrench. An open-end wrench will work if a flare nut wrench is unavailable, just be careful not to strip the sensors if they are to be reused.

Once the oxygen sensors have been removed, use a reciprocating saw to cut the converters out of the Y-pipe assembly.  Starting the cuts on the converter side of the welds is best approach. Cutting through the weld can be difficult, as this thickest and hardest portion of the pipe. Once the converter has been liberated from the Y-pipe, inspect it for obvious damage. The honeycombing on this converter had melted together and approximately 50% of it was missing.

Using a sanding wheel on a 4" grinder, grind off the residual welds and rust on the pipe.  Approximately 2" of the pipe will need to be prepped for welding.

Comparison of the stock catalytic converters and new Maremont unit.

Using a bench vise, slightly oval the (4) 2.25" OD pipe pieces (slip collars). A very slight oval helps the slip collar stay in place when fitted onto the receiving pipe. Place a slip collar onto each end of the Y-pipe flanges and tack weld in 2 places. Now, bolt the Y-pipe flanges back to the exhaust manifolds. Keep in mind that the shorter of the two flanges goes to the driver¡¯s side.

Next, using the assistance of a helper, slide the converters, rear slip collars and rear Y-pipe assembly on Y-pipe flanges. Use the muffler flange as a guide for centering the Y-pipe assembly in place. If the anything is touching the frame rails, drive shaft, transfer case, etc¡¦ simply shift the Y-pipe on the slip collars until there is a uniform space between the pipe and it's surrounding parts. Once the Y-pipe is aligned correctly, bolt the rear flange to the muffler flange, and tack weld all the pipe pieces into place.

Now, remove the muffler flange bolts, the (6) 13mm nuts from the exhaust manifold and gently lower the Y-pipe assembly from the vehicle. Place on a workbench and weld all tack-welded seams.

Clean oxygen sensor bung with a very light spray of brake cleaner and a wire brush. When the brake cleaner has evaporated, gently blow out the threads. Lightly wipe the shielded end of the oxygen sensors and apply a very light dab of anti-seize to the threads. Install oxygen sensors.

Install Y-pipe assembly with new exhaust manifold gaskets, tighten (6) 13mm nuts, and reconnect oxygen sensors.

PART 2: MUFFLER INSTALLATION

Remove muffler assembly by sliding the hangar pin keepers out of the rubber grommets (3 total). Slide muffler assembly forward and rotate until the rear of the pipe clears the rear axle.

Comparison of the stock muffler and the MAREMONT OE replacement.

Starting at the rear of the muffler, remove there pipe assembly from muffler just behind exhaust hanger pin.

On the front end of the muffler, remove the flange by cutting approximately 3" from the edge of the flange. Once the flange has been removed from the muffler, make a second cut at the taper on the flange. This taper has approximately the same inner diameter and the new mufflers outer diameter. If you cut to far up the taper, gently ease in the edge of the taper using a pair of pliers or channel locks. Continue until the flange fits snugly over the muffler inlet.

Bolt the muffler flange, exhaust olive and Y-pipe assembly together.

Install the rear section of exhaust pipe in the vehicle, using the rear pin keeper and a strap to hold in place.

Using a piece of 2.25" inner diameter pipe cut approximately 2" -3" long (i.e. slip collars from above) insert into the rear section of exhaust pipe. Install the muffler into the vehicle by sliding the front into the tapered flange and the rear onto the rear slip collar. Adjust the muffler so that there is ample clearance between it and surrounding parts. Tack-weld and remove from vehicle.

Place assembly on bench and weld seams.

Install muffler assembly on rear hanger pin, install exhaust olive, and tighten muffler flange. The last thing you'll need to do is cut off the (2) remaining hanger pins from the stock muffler. Install the hanger pins in to the rubber keepers, and weld onto pipe to support muffler assembly.

RECYCLING:

Once you have finished your exhaust project, call a local metal recycling center in your area and ask if they buy back converters. The local metal salvage yard paid me $190 for converters that I removed. Catalytic converters are made up of precious metal and are very desirable to the local salvage centers.

DISCLAIMER:

EPA/CARB compliance was not addressed in this tech write-up, if you live in California, be sure to check that you are replacing your converters with a CARB compliant units. Also, when possible I listed a CARB/50-state rated converter, but be aware that not all of the units listed are 50-state compliant.