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S54 Engine Catalytic Converter Replacement
 
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Pelican Technical Article:

S54 Engine Catalytic Converter Replacement

Nick Czerula

Time:

6 hours6 hrs

Tab:

$1200

Talent:

*****

Tools:

Set of sockets 8mm, 10mm, 12mm, 13mm, plastic scraper

Applicable Models:

BMW Z4 Coupe/Conv (2006-08)

Parts Required:

Catalytic converters (headers), gaskets, exhaust clamps, hardware and gaskets for full exhaust

Hot Tip:

Work with a cool exhaust

Performance Gain:

Replace mufflers

Complementary Modification:

Replace in pairs

The catalytic converter's job is to clean up the exhaust leaving the engine to meet emission standards. In a catalyst (cat for short) exhaust gases are forced to pass through a fine-meshed ceramic matrix impregnated with platinum-iridium alloy. These metals bring unburned CO and hydrocarbon molecules together with excess oxygen in the exhaust and accelerate oxidation. This chemical reaction creates heat and the heat further improves oxidation efficiency; therefore cats need to run at a high temperature for maximum efficiency. Over time the high heat as well as contaminants in the exhaust melt or otherwise damage the ceramic matrix in the cat so that it requires replacement.

BMW Z4M models with an S54 engine utilize four catalytic converters, two mounted to the outlet of each header and two (integrated) in the H-pipe. Catalyst replacement is a big job and requires removing the complete exhaust system and many other components. Read through the procedure thoroughly before beginning. Plan for this job to take a day, if all goes as planned. To replace the H-pipe header, see our tech article on exhaust system replacing. This article will cover replacing the exhaust headers with integrated catalytic converters on BMW Z4M models.

A damaged catalytic converter can rarely be diagnosed visually. Catalyst failure usually sets fault codes in the ECM. Before you remove the exhaust system, use a BMW scan tool or equivalent to download fault codes and determine if there is any reason to suspect the failure of these major emissions control components or of the oxygen sensors. The oxygen sensors, particularly those downstream of the catalysts, may be easier to remove once the exhaust system is off the car.

The most common fault codes that show your catalytic converters are faulty include: P0420 Catalyst System Efficiency Below Threshold (Bank 1) or P0430 Catalyst System Efficiency Below Threshold (Bank 2). Bank 1 refers to the catalyst attached to the front three cylinders (1-3). Bank 2 refers to the catalyst attached to the rear three cylinders (4-6).

You do not have to replace both cats at the same time. Replacing only the faulty one can save quite a bit of money. However, keep in mind, if one is faulty the other may not be far behind. When dealing with the previously mentioned fault codes, check that the engine is running well and there are no other fault codes stored before condemning the cats.

When removing the exhaust system, have new fasteners, gaskets and rubber insulators on hand to help complete the repair.

When removing the exhaust system and particularly if you are going to store it while other repairs are taking place, be sure to protect the oxygen sensors and their electrical leads. Do not drag the exhaust system on the ground carelessly.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please include your vehicle information.

Raise and support the rear of the vehicle on jack stands. See our tech article on jacking up your vehicle. Wear those safety glasses whenever you work under your automobile.

Remove the exhaust system. See our tech article on exhaust system replacing. It's a good idea to remove the oxygen sensors to prevent damage, however it is not necessary. To do so, see our tech article on oxygen sensor replacing. It's also a good idea to remove the exhaust gas sensor to prevent damage, however it is not necessary. To do so, see our tech article on exhaust gas temp sensor replacing.

BMW Z4M models with an S54 engine utilize four catalytic converters, two mounted to the outlet of each header and two (integrated) in the H-pipe.
Figure 1

BMW Z4M models with an S54 engine utilize four catalytic converters, two mounted to the outlet of each header and two (integrated) in the H-pipe. Bank one catalyst in in the front header (red arrow), while bank 2 catalyst is in the rear header (blue arrow). To replace one header, both have to be removed. It is worthwhile to replace them as a pair due to this configuration.

To make room to work, remove the secondary air pump and hoses, see our tech article on secondary components replacing.
Figure 2

To make room to work, remove the secondary air pump and hoses, see our tech article on secondary components replacing. Start by removing the crankcase breather hose. Disconnect the electrical connector (inset) by pressing the wire release and pulling the connector straight off. Then lift the solenoid (green arrow) up and out of the mounting bracket. Next, detach the breather hoses from the intake and breather (red arrows).

To remove the breather hoses, squeeze the collar and pull straight up.
Figure 3

To remove the breather hoses, squeeze the collar and pull straight up.

Place breather hose and solenoid aside (green arrow).
Figure 4

Place breather hose and solenoid aside (green arrow). You can leave the rubber hose attached. It only has to be moved enough to make room for the engine cover to come out.

Remove the six 10mm engine cover fasteners (red arrows).
Figure 5

Remove the six 10mm engine cover fasteners (red arrows). Then remove the oil filler cap (green arrow).

Lift and remove the engine cover.
Figure 6

Lift and remove the engine cover.

Working at the rear corner of the cylinder head, pull the wiring harnesses (red arrows) out of the holders.
Figure 7

Working at the rear corner of the cylinder head, pull the wiring harnesses (red arrows) out of the holders.

Working at the rear corner of the cylinder head near the camshaft sensor (purple arrow), remove the 13mm heat shield fastener (red arrow).
Figure 8

Working at the rear corner of the cylinder head near the camshaft sensor (purple arrow), remove the 13mm heat shield fastener (red arrow).

Then, remove the three 10mm fasteners (purple arrows) then remove the secondary air check valve, remove the 13mm heat shield fasteners (red arrows).
Figure 9

Then, remove the three 10mm fasteners (purple arrows) then remove the secondary air check valve, remove the 13mm heat shield fasteners (red arrows).

Working at the rear corner of the cylinder head, pull the wiring harnesses (red arrow) out of the heat shield.
Figure 10

Working at the rear corner of the cylinder head, pull the wiring harnesses (red arrow) out of the heat shield.

Lift and remove the heat shield (red arrow).
Figure 11

Lift and remove the heat shield (red arrow).

Locate the oxygen sensor electrical connectors at the rear of the cylinder head.
Figure 12

Locate the oxygen sensor electrical connectors at the rear of the cylinder head. Label or mark the wiring harness to aide during reinstallation. I suggest replacing one sensor at a time so you do not mix up connectors. Bank 1 Sensor 1, red arrow. Bank 2 Sensor 1, purple arrow. Press the release tab and pull the electrical apart (inset).

Unclip and lift up the wiring harness housing.
Figure 13

Unclip and lift up the wiring harness housing. Squeeze the tabs (red arrows) and flip up. Then remove the electrical connector for the sensor you are replacing from the holder. Disconnect the electrical connector by pulling it straight apart (inset).

You now have access to the headers.
Figure 14

You now have access to the headers. Working at each of the six header connections at the cylinder head, remove the three 11mm nuts (red arrows). The blue arrow shows a 1/4 drive ratchet under the header to remove the lower hidden nut. Do this for each of the six connections. Support the headers as you remove the final nuts.

Pull the header away from the cylinder and off the mounting studs.
Figure 15

Pull the header away from the cylinder and off the mounting studs.

Remove the front (red arrow) and rear (blue arrow) headers together through the bottom of the vehicle.
Figure 16

Remove the front (red arrow) and rear (blue arrow) headers together through the bottom of the vehicle.

Once removed, remove all the gaskets and clean the sealing surfaces (red arrows).
Figure 17

Once removed, remove all the gaskets and clean the sealing surfaces (red arrows).

Working above the cylinder head, clean the sealing surface for the gasket using aplastic scraper (red arrow).
Figure 18

Working above the cylinder head, clean the sealing surface for the gasket using aplastic scraper (red arrow). If the removing the nuts pulled the studs out (blue arrows) use new studs.

If you feel the need to reuse the studs to save money, use a stud extractor socket to counterhold the stud as you remove the nut.
Figure 19

If you feel the need to reuse the studs to save money, use a stud extractor socket to counterhold the stud as you remove the nut. Once all the studs are in good shape and the sealing surfaces clean, install the gaskets onto the cylinder head studs. Then feed the headers onto the studs and install the nuts finger tight. Tighten all the nuts in an alternating pattern beginning in the center of each header, working outward. Once tight, reassemble all other items. Check the exhaust to be sure it is sealed and clear any fault codes.

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Page last updated: Sat 12/3/2016 03:07:41 AM