Difficulty Level: 5
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten
This article is one in a series that have been released in conjunction with Wayne's
101 Performance Projects for Your BMW 3 Series. The book
contains 272 pages of full color projects detailing everything
from performance mods to timing the camshafts. With more than 650+ full-color
glossy photos accompanying extensive step-by-step procedures, this book
is required reading in any 3 Series owner's collection. The book was
released in August 2006, and is available for ordering now. See
The Official Book Website
for more details.
Let me start off by congratulating the BMW engineers for squeezing the E36
six-cylinder engine into an almost impossibly tight spot. It is quite a
remarkable packaging job, considering they did it in the early 1990s when
all they had were computers with 386 processors and rudimentary 2D CAD
programs. Yet their success makes it a big pain for mechanics who work on
these carsóitís a tight squeeze, and you have to remove a lot of stuff to
remove the intake manifold.
The best way to learn how to remove the intake manifold is to carefully
follow along with these pictures. This task includes one of the steps in the
head gasket replacement (Project 17), so a number of other items have
already been removed (fan, radiator, belts, etc.). If youíre just pulling
the intake manifold, you donít need to remove these other items.
For this project, I strongly recommend that you get a digital camera and
take about a hundred photos of the disassembly process. If you have any
questions as to how it was put together beforehand, you can easily refer
back to the photos. As an additional resource, the companion CD-ROM to this
book (available at www.101Projects.com) contains approximately 300 more
photos of the manifold removal and installation process.
Before you begin, let the car sit for about six hours before working on it.
The pressure in the fuel lines should have dissipated somewhat, and the car
should be stone cold while youíre working on it. Disconnect the battery (see
Project 84), as you will be working very close to the starter, which has
live current running to it at all times. You will also be disconnecting fuel
lines near this connection and donít want to risk any sparks. Additionally,
remove the gas cap from the gas tank to relieve any pressure that may have
built up inside the tank from expanding fumes.
Since installation is simply the reverse of removal, just hook everything
back upóbut carefully inspect the intake boot for cracks prior to doing so.
Consider replacing the intake boot while youíre in there, as it may start to
crack and break once youíve disturbed it. Also, watch out for the lower rear
manifold mounting bracket, as it can be very difficult to reattach (see
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The air filter housing.
The blue arrow points to the air intake channel that feeds the air filter.
Remove the air filter housing and this channel by disconnecting it at the
clips (orange arrows).
The throttle body and
mass airflow sensor assembly are shown here. The two hoses located below
that assembly need to be disconnected (orange arrow). Disconnect the
electrical harness to the airflow sensor so you can move the sensor around
easier (blue arrow). Disconnect the rubber boot from the sensor and the
throttle body by releasing the clamps (yellow arrows). Check this boot
carefully, as it often cracks and can cause erratic idling if it does.
Disconnect the throttle body from the intake manifold (top two with the
red arrows). At this point, you should be able to pull away the throttle
body. Also, disconnect the vacuum hose that supplies the brake booster
(green arrow), and detach the oil dip stick guide tube and the vent hose
at the base of the dip stick.
Be careful of the
throttle body cables when you detach the throttle body, as you donít want
to twist or damage them. Also, do not disconnect the hoses that
connect to the throttle body from underneath.
Disconnect the two fuel lines that circulate fuel through the injector
rail. Carefully disconnect the clamps from the pipes that exit out of the
bottom of the manifold (blue arrows). For S52/M52 engines, you may need
special BMW tool 16-1-050 to release these fuel lines (purple arrows).
Thereís also a clamp that holds the two metal lines underneath the
manifold. Remove this clamp as well (look down the tunnel under the
manifold for access). When reinstalling the manifold, the most frustrating
attachment point was the bracket shown by the yellow arrow (remove this
bolt after you have disconnected the fuel lines). A single bolt fastens
the bottom of the manifold to this bracket, but getting that bolt threaded
back into the hole was very difficult, because you canít see if the
manifold is aligned with the bracket (misaligned in the photo). Use a
small inspection mirror and an assistant to help you guide the bolt back
into its proper place in the manifold. Thereís a similar bolt and bracket
combination toward the front of the car.
This photo shows a
close-up of the fuel injector plugs after the harness has been removed.
The valve cover breather hose (yellow arrows) must be disconnected. The
rearmost intake manifold nuts (inset) can be difficult to get to, so I
recommend using swivel sockets for this task (see Photo 1 of Project 49).
To remove the intake
manifold, you need to remove the engine wire harness first and slide it
out of the way. Start by unscrewing the main plugs (green arrows, lower
right). Then, loosen the main wire junction box (blue arrow) by lifting up
the rain tray under the wipers and removing the two small screws contained
within (red arrow, upper right). Let the harness hang looseóyou will need
to push it out of the way when you lift out the manifold. Even more
annoying than removing the wire harness, you need to disconnect a hosethat
is located underneath the manifold, inside the tunnel below the plastic
manifold runners (yellow arrow). Reach in and disconnect the plastic clip
on the hose. It was a tight squeeze for my hand, so you may need to ask
someone with small hands for help. The purple arrow shows the fuel
injector wire harness pushed off to the side.
disconnected, the manifold should lift up out of the engine compartment
but not without a fight. The manifold is tightly squeezed in between the
cylinder head and the firewall (near the wipers). You will have to wrestle
with it a bit to get it off the studs that attach it to the cylinder head.
Double- and triple-check your connections to make sure you didnít forget
to disconnect a hose or line.
While you have the intake manifold apart, you should replace a few
important seals. The first is the throttle body seal, shown on the right.
It seals the throttle body housing to the intake manifold. A leak in this
gasket can cause poor running and an erratic idle. On the left, one of the
manifold-to-head gaskets is shown. These gaskets can also cause erratic
engine performance if there are leaks around them. If the seal is
breached, it will create a vacuum leak, and the engine may suck in
additional air on the intake stroke, altering the air/fuel mixture ratio
for that particular cylinder.