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Exhaust Manifold Replacement
 
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Pelican Technical Article:

Exhaust Manifold Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$200 to $1,200

Talent:

*****

Tools:

Set of sockets, flathead screwdriver, hydraulic floor jack and jack stands

Applicable Models:

BMW Z3 (1996-02)

Parts Required:

Exhaust manifold, Exhaust manifold gaskets, Exhaust fasteners

Hot Tip:

Work with a cool exhaust

Performance Gain:

Replace faulty exhaust manifold or catalytic converters

Complementary Modification:

Install aftermarket header

The exhaust system of any gasoline powered passenger vehicle sold in the US since 1996 is required to be equipped with a catalytic converter. 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 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.

In the 4-cylinder engine and early 6-cylinder engines in Z3 vehicles, the catalyst(s) are bolted to the exhaust manifold. After the cat comes the muffler and the rest of the exhaust system. Beginning with 2001 models, the 6-cylinder engine exhaust manifolds were integrated with the catalysts.

A damaged catalytic converter can rarely be diagnosed visually. Catalyst failure usually sets fault codes in the engine control module (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.

Exhaust manifold and 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.

When replacing your exhaust manifold, have new gaskets, manifold nuts and flange studs ready. If replacing gaskets due to exhaust leak, inspect the manifold closely for cracks or warping. Before removing the flange nuts, clean them with a wire brush and spray penetrating oil on the threads. Allow it to soak in before attempting to remove the nuts. The flange studs have a tendency to break. If this happens to you, no sweat; once the manifold is removed you can easily replace them.

On post-2001 models: The catalytic converter and exhaust manifold for each bank of cylinders (cylinders 1--3 and cylinder 4--6) is one item. You have to remove both exhaust manifolds together even if you're replacing only one. 

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

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 leave your vehicle information.

Raise and support front of vehicle on jack stands. See our tech article on jacking up your vehicle.

Models with 4-cylinder engine:
Models with 4-cylinder engine - Working at front of exhaust system, remove nuts that connect exhaust system to exhaust manifold (green arrows).
Figure 1

Models with 4-cylinder engine - Working at front of exhaust system, remove nuts that connect exhaust system to exhaust manifold (green arrows). Be careful when loosening these nuts. I like to spray studs with penetrating oil and clean the end of stud with a wire brush before removing. Depending on your region, these can seize up. If they break, don't worry. You can remove the studs by hammering them out and replace with new ones. Depending on if the nuts haven been replaced, they could 16, 17 or 18mm. Once the exhaust has been unbolted from the manifold, you will have to unbolt the manifold from the head. Start by removing the ignition coil and wires. Remove the engine cover. See our tech article on engine covers removing.

Models with 4-cylinder engine - Rotate the electrical connect counterclockwise to disconnect (green arrow).
Figure 2

Models with 4-cylinder engine - Rotate the electrical connect counterclockwise to disconnect (green arrow).

Models with 4-cylinder engine - Next you can remove the two 8mm nuts (green arrows) from the ignition coil mounting bracket studs.
Figure 3

Models with 4-cylinder engine - Next you can remove the two 8mm nuts (green arrows) from the ignition coil mounting bracket studs.

Models with 4-cylinder engine - Lift the ignition coil up and off the mounting bracket and lay aside.
Figure 4

Models with 4-cylinder engine - Lift the ignition coil up and off the mounting bracket and lay aside.

Models with 4-cylinder engine - Next you have to loosen the two 10mm ignition wire loom fasteners (green arrows).
Figure 5

Models with 4-cylinder engine - Next you have to loosen the two 10mm ignition wire loom fasteners (green arrows). Loosen the nuts about three turns.

Models with 4-cylinder engine - Then slide the ignition loom with mounting bracket (green arrow) up and out of valve cover.
Figure 6

Models with 4-cylinder engine - Then slide the ignition loom with mounting bracket (green arrow) up and out of valve cover.

Models with 4-cylinder engine - Once the loom is free, remove each spark plug wire from the spark plugs.
Figure 7

Models with 4-cylinder engine - Once the loom is free, remove each spark plug wire from the spark plugs. Then remove the ignition wires and ignition coil as a unit. Store them is a safe place. Now you are going to have to remove the secondary air pipe along with the check valve. I like to remove them as one unit and leave the hose connected. This makes it easier and much faster.

Models with 4-cylinder engine - First you have to disconnect the secondary air pipe.
Figure 8

Models with 4-cylinder engine - First you have to disconnect the secondary air pipe. To disconnect the pipe from the secondary air valve. Squeeze the release tabs, then pull the pipe straight off.

Models with 4-cylinder engine - Working at the front of the cylinder head, remove the three 10mm fasteners for the secondary air check valve and mounting bracket.
Figure 9

Models with 4-cylinder engine - Working at the front of the cylinder head, remove the three 10mm fasteners for the secondary air check valve and mounting bracket. Two are two bolts and one is a nut (green arrows).

Models with 4-cylinder engine - Working at the exhaust manifold flange, remove two 11mm nuts from the secondary air pipe.
Figure 10

Models with 4-cylinder engine - Working at the exhaust manifold flange, remove two 11mm nuts from the secondary air pipe. In this photo I am using a mirror to show the location of the secondary air pipe nuts (green arrows). The yellow arrow points to one of the 11mm exhaust manifold flange nuts you will remove later. Remove both secondary air pipe 1mm nuts, then remove the secondary air pipe from the exhaust manifold. With the pipe remove, clean all of the old gasket off the pipe.

Models with 4-cylinder engine - This photo shows a better view of the secondary air pipe nuts (green arrows) and the exhaust manifold nuts (yellow arrows).
Figure 11

Models with 4-cylinder engine - This photo shows a better view of the secondary air pipe nuts (green arrows) and the exhaust manifold nuts (yellow arrows). All are 11mm nuts. Once the secondary air pipe is removed, removed the exhaust manifold nuts, then remove the exhaust manifold from the vehicle.

Models with 4-cylinder engine - With the exhaust manifold removed, you can replace any broken flange studs.
Figure 12

Models with 4-cylinder engine - With the exhaust manifold removed, you can replace any broken flange studs. Put the manifold in a vise, (be careful not to crush or bend it) and knock out the studs using a hammer. Install new manifold and gaskets on cylinder head, be sure to align manifold outlet flanges with exhaust pipes while installing. Then install new mounting nuts by hand, run them down to manifold. Then tighten manifold nuts. Install secondary air valve and pipe. Install exhaust pipe to manifold nuts and tighten. Reinstall ignition coil and wires. Reassemble remaining items and check exhaust system for leaks. .

Models with 6-cylinder engine:
Models with 6-cylinder engine - The 6-cylinder portion of this tech article was performed on an M54 engine on BMW.
Figure 13

Models with 6-cylinder engine - The 6-cylinder portion of this tech article was performed on an M54 engine on BMW. The manifold set up is very similar to Z3 and these steps can help you replace the exhaust manifolds. Remove all four oxygen sensors from exhaust manifold. This will help you avoid accidentally damaging the sensors. See our tech article on oxygen sensor replacing. Working at front of exhaust system, remove nuts that connect exhaust system to exhaust manifold (green arrows). Be careful when loosening these nuts. I like to spray studs with penetrating oil and clean the end of stud with wire brush before removing. Depending on your region, these can seize up. If they break, don't worry. You can remove the studs by hammering them out and replace with new. Support engine from below using a hydraulic floor jack with a block of wood between jack and engine. Next, working at right front of cylinder head, remove secondary air valve from engine. See our tech article on secondary air components replacing.

Models with 6-cylinder engine - Working in engine bay, locate top of right engine mount.
Figure 14

Models with 6-cylinder engine - Working in engine bay, locate top of right engine mount. Photo shows mount looking down past exhaust manifold. Remove nut from motor mount (green arrow). Remove right side engine mount bracket fasteners, then remove bracket from engine. The bracket has four fasteners and bolts to the side of the engine block. You can access it from below the vehicle.

Models with 6-cylinder engine - Remove exhaust manifold fasteners (green arrows).
Figure 15

Models with 6-cylinder engine - Remove exhaust manifold fasteners (green arrows). There are eight fasteners on each manifold. Remove the front manifold fasteners first, then rear manifold fasteners. This photo shows the manifolds with engine removed for clarity. Once fasteners have been removed, pull exhaust manifold away from cylinder head and remove from engine compartment. Remove front manifold, cylinders 1-3, then remove rear manifold, cylinders 4-6. Do not drop exhaust manifolds when removing. The catalytic converters are fragile and can be damaged from an impact.

Models with 6-cylinder engine - With the exhaust manifold removed, you can replace any broken flange studs.
Figure 16

Models with 6-cylinder engine - With the exhaust manifold removed, you can replace any broken flange studs. Put the manifold in a vise, (be careful not to crush or bend it) and knock out the studs using a hammer. Install new manifold and gaskets on cylinder head, be sure to align manifold outlet flanges with exhaust pipes while installing. Then install new mounting nuts by hand, run them down to manifold. Then tighten manifold nuts. Install engine mounting bracket to engine and tighten. Install engine mount upper nut and tighten. Install secondary air valve to cylinder head. Install exhaust pipe to manifold nuts and tighten. Reinstall oxygen sensors, use anti-seize paste on thread. Reassemble remaining items and check exhaust system for leaks.

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Page last updated: Sat 12/3/2016 02:07:51 AM