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Removing Your Exhaust Manifold
 
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Pelican Technical Article:

Removing Your Exhaust Manifold

Nick Czerula

Time:

2 hours2 hrs

Tab:

$200

Talent:

***

Tools:

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

Applicable Models:

BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)

Parts Required:

Exhaust manifold gaskets, Exhaust fasteners

Hot Tip:

Work with a cool exhaust

Performance Gain:

Replace faulty exhaust manifold or catalytic converters

Complementary Modification:

Replace your exhaust hangers

The E46 6-cylinder engine is equipped with two exhaust manifolds (bank 1 = cylinders 1-3, bank 2 = cylinders 4-6). Each manifold ducts the exhaust to a built-in 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.

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.

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. 

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 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 you are 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. Never 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. Do you have 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 the vehicle on jack stands. See our Pelican Parts technical article on Jacking Up Your BMW

Remove all four oxygen sensors from the exhaust manifold. This will help you avoid accidentally damaging the sensors. See our Pelican Parts technical article on Replacing Your Oxygen Sensors.

Working at the front of the exhaust system, remove the nuts that connect the exhaust system to exhaust the manifold (green arrows).
Figure 1

Working at the front of the exhaust system, remove the nuts that connect the exhaust system to exhaust the manifold (green arrows). Be careful when loosening these nuts. I like to spray the 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, donÂÂÂÂÂ't worry. You can remove the studs by hammering them out. Support the engine from below using a hydraulic floor jack with a block of wood between the jack and the engine. Next, working at the right front of the cylinder head, remove the secondary air valve from the engine.

Working in the engine bay, locate the top of the right engine mount.
Figure 2

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

Remove the exhaust manifold fasteners (green arrows).
Figure 3

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

Install new the manifold and gaskets on your cylinder head, be sure to align the manifold outlet flanges with exhaust pipes while installing. Then install the new mounting nuts by hand, run them down to manifold. Then tighten manifold nuts. Install the engine mounting bracket to the engine and tighten. Install the engine mount upper nut and tighten. Install the secondary air valve to the cylinder head. Install the exhaust pipe to the manifold nuts and tighten. Reinstall the oxygen sensors, use anti-seize paste on the threads. Reassemble the remaining items and check the exhaust system for leaks.

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Comments and Suggestions:
Norcal Dude Comments: Reference The Gr8 design's question from 2 years ago, I don't know how you could do this without removing the subframe on an E46. That was the key to me getting it done and is mentioned in the Bentley manual. Maybe the different models might not require it but my 2001 330i did. I also used my Harbor Freight engine support bar that I bought for my oil pan gasket repair. That seemed to give me a little extra clearance that I needed for getting the 1st Bank Cyl 4-6 out. An 11MM Ratcheting wrench would have been nice but I made do with my tools on hand and a lot of elbow grease. Not being in a hurry is key to getting this done also - you will be challenged...
May 27, 2017
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Tony Comments: I have a 2005 325i and I show 6 codes 0300,0301,0302,0303,0313 & 0444. It starts and idles ok but then engine start shaking randomly. Throttle response is very minimal. I turn off car and then turn back and then its like it resets and throttle response gets better. Although, it is still extremely low on bottom end power. Can this be the cats?
May 25, 2017
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders. Also confirm there are no vacuum leaks. - Nick at Pelican Parts  
S3bas Comments: I have been having oil pool up on the spark plugs, I have changed the valve cover gasket and plastic washers . I am not sure we're the oil is comming from . I have bad catalyc converters witch I'm changing next week . Could the bad catalyc converters/headers be pushing gunk back up the engine . I also saw black grit . I was told it could possibly 've failling pistons
April 25, 2017
  Followup from the Pelican Staff: Not likely. I would assume the valve cover has a crack in it, allowing oil to escape. Best bet is to remove the valve cover and leak test it or have someone with a co2 leak detector check it when installed. - Nick at Pelican Parts  
Fox Fader Comments: You can forget about hammering those studs out whether air hammering or by hand, cause if they break, those things are FROZEN in place something fierce. Ask me how I know.
April 24, 2017
  Followup from the Pelican Staff: I can usually get them out no problem. We are in a salt belt. I will say, the studs usually break if you don't heat them first. - Nick at Pelican Parts  
Justin Comments: When I jack up the engine, just enough to support it. Do I need to disconnect anything else like the fan, etc?

2005 325i automatic.
April 10, 2017
  Followup from the Pelican Staff: If raising it more than an inch or so, remove the cooling fan. - Nick at Pelican Parts  
S3bastian Comments: I am always getting codes for cylinder missfire for bank 2 ... Cinders 4,5, and 6
I can checked for vacumm hoses , and change fuel filter and fuel pump . And valve cover gasket along with the ccv. Upper and Lowe intake boots changed and disa boring replaced . Could it be a bad catalog converter car has 207,000 miles I don't think it's ever been changed
March 24, 2017
  Followup from the Pelican Staff: Yes, you can have the backpressure tested, catalytic converters FYI usually set a fault for high RPM high load which is almost specific to that type of failure. Below 1 PSI is the unwritten spec for the acceptable backpressure, most often it'll be close to zero. - Casey at Pelican Parts  
DJ Lil BASTARD Comments: 2003 BMW 325I SPORTSWAGON I will be driving and get the car upto 6500rpm's or just need to get on freeway and the car beeps loud I lose power, and if I shift into N and turn key off and on it will run fine, if I dont shut off and on I have no power, still runs but rev's up and down almost stalling. I found big cracks on my top intake boot so i replaced it with K&N 57i 1002 cold air system but still running into same problem. My car has just started sounding like it has exhaust leak and it sounds like its at the manifold. What shoud i do the car came from AZ and anything rubber is in bad shape. Help thx DJ Lil BASTARD
January 18, 2017
  Followup from the Pelican Staff: Is the check engine light on or flashing when the problem is present? if you have a fuel trim fault, it could be more vacuum leaks or unmetered air. Or a fuel delivery issue. - Nick at Pelican Parts  
Sroor9001 Comments: Is it same procedure in e39 525 model 2002
November 28, 2016
  Followup from the Pelican Staff: It will be different due to component and location differences on the models. You can use it as a rough guide though. - Nick at Pelican Parts  
nj123 Comments: I am getting a high O2 reading bank 2 post cat sensor. Will oil dripping down from a previous leaky valve cover gasket cause onto bank to exhaust manifold cause it to leak and make a high O2 content exhaust?
October 6, 2016
  Followup from the Pelican Staff: It can ruin the sensor if oil gets into the top where the wires enter. - Nick at Pelican Parts  
kris.b30 Comments: Ok. What about us guys with RHD e46 ? On a close look I cant think of a way to get around the nuts on the back as the steering is in the way.
August 25, 2016
  Followup from the Pelican Staff: I don't have any experience with RHd models. You may want to remove the steering shaft. - Nick at Pelican Parts  
NyKoLe Comments: Why does white smoke come out my exhaust when I drive it I have a 2002 bow 325i I wanna know what's the problem or how do I change it
December 23, 2015
  Followup from the Pelican Staff: White smoke is likely coolant. I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty.
- Nick at Pelican Parts
 
The Gr8 design Comments: Will I need to remove my front subframe to do this. I plan on replacing them with carless headers. O3 330xi
June 10, 2015
  Followup from the Pelican Staff: I haven't done headers on an E46, but I recall the guys in the shop just removing the right side engine mount and bracket. Not the subframe. - Nick at Pelican Parts  

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Page last updated: Fri 6/23/2017 02:22:00 AM