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[Marks DTM Calib]

As with any engine, the key to reliability is effective servicing.

When combustion occurs, blow by gases (the fumes which pass by the piston rings), accumulate within the engine casing.

In years gone by, these fumes would have been vented to atmosphere (if you were lucky there may have been a catch tank) but, emission rules mean that this is no longer an option.

As a result, engine manufacturers 'capture' these gases and feed them into the inlet to be burnt and expelled via the exhaust. This is all carried out by the engine breather setup.

In addition to the blow by gases, some oil vapour also passes through these breathers and this is a key contributor to the 'blocking' issue. This is made worse if the oil is old and 'past its best' as it takes on a tar like constituency.

So, onto the cleaning

To start, its recommended that you have the following items:

• Carb cleaner (or similar suitable cleaner)
• Breather bridge to plenum seal 1 off required - 90467543
• Breather bridge to throttle O ring 2 off required (4 off on extended plenum's) - 90500983

All of the above is cheap.

Remove the plenum as detailed in:

V6 Plenum Removal

Using a flat blade screwdriver, ease the ecotec cover off so as to expose the torx retaining screw for the breather bridge assembly.



Remove the 4 TORX bolts and separate the throttle body from the plenum. Now remove the torx bolt holding the breather bridge to the plenum and lift it off. On later units with the extended plenum assembly, an additional short breather section is fitted, this should be removed and cleaned in the same way as the main breather bridge.



The next pic shows the three parts removed, the throttles at the front, the breather bridge to the left and the plenum in the center.



The black breather bridge needs a good shot of Carb cleaner and pay particular attention to the underside where there should be 4 smallish holes visible.



Spend plenty of time cleaning the throttle assembly, paint stripper is excellent for removing the tough carbon off the rear of the butterflies as is Carb cleaner, pay close attention to the edges of the throttle butterflies.

This is also a good time to check the throttle butterflies, they should close pretty much fully shut (within machining tolerances anyway) but, don't over do it as they can stick shut.

Its not unknown for some mechanics to wind the throttle stop in to overcome stalling issues. This is a BAD idea as it means the idle is no longer under ECU control and the ECU can not effectively compensate for varying idle demands from air con, steering input and alternator loads.

So check the setting is adjusted so that the throttles are shut but they don't stick (if you wind out the throttle stop until you can just feel it stick, then wind it back in half a turn is about right!)

When these items are clean, fit the new seals to the breather bridge, re-assemble the plenum system ready to re-fit to the car as shown. Its worth putting a thin wipe of grease on the seals of the breather bridge to aid assembly.



And yes, that is the same plenum as in the first picture!

Remove the 2 breather tubes - 1 small one from the breather box, 1 large one that divides into two from the same breather box.

Next we need to clean the vent housing, this is mounted at the rear of the 1-3-5 head (driver's side in the UK) and has two connections located on the top face, one small and one large.

The smaller pipe (brass) has a very small hole in the center, this can be cleared with ideally a small drill (approx 1.6mm) or a suitable piece of wire.



Its also worth cleaning the area around the breather holes for completeness (and it makes it look nice!)

Next, the big pipe.



Again, a drill bit is recommended as this ensures that crud is removed (twist the drill as you go) rather than pushed into the breather box.

Do beware of squirting loads of Carb cleaner into the breather holes as this will have an adverse effect on the oil.

[Marks DTM Calib]

Now to clean the two breather pipes.

Before starting, check the tubes for damage and splits, if you find any then you can get away with removing short pieces of tube (10-20mm) and still get the items to fit comfortably.

So, onto the smaller of the tubes.

The method I use is to block off one of the ends and half fill it with carb cleaner, shake it well for a few minutes and then blast it through with more carb cleaner to get it nice and clean. A final rinse with water can be used but, make sure its dry (shake it well) before re-fitting.

The larger tube is a little harder due to the Y piece but, the same method works well. Again, a good blast through with water gives a good final rinse.

Re-assembly is the reverse of removal!

Torque Values
EGR pipe to EGR valve 25Nm

Item	Value
Plenum to inlet	8Nm
Support bracket to EGR valve	20Nm
Cable tray to plenum	6Nm
Throttle body to plenum	8Nm
Breather bridge to plenum	8Nm

[feeutfo]

This is taken from my 03 3.2v6. Earlier models differ slightly I believe in as much as the rubber flap is built into a gasket used to seal the box to block.


Where it sits ,and the holes into crank case, behind cylinder 5 which is the big lump on the right. Coolant transfer pipe top left and bell housing are visible in the back ground, as is a coolant leak top of picture is the oil cooler cover plate and one of it's bolts.



Exhaust manifold heat shield shown at the bottom of the pic needs bending out the way to reach two of the torx bolts. Scuttle and wiper motor also need to be removed for access.


Breather box itself shows some baffles and a rubber flap. Center rivet needs to be drilled out and and tapped with a new bolt to refit the cover which appears to be sealed with something similar to cam cover sealant. Box itself is sealed to the block with same grey goo used for the oil cooler cover plate.



Breather pipe exits.

These are the brass pipes that exit the breather box to the two rubber pipes to plenum.



The smaller one more clearly shown was blocked on mine and was the reason for removal to see what was going on. It had simply sealed over and gone hard and I could have just forced the blockage through with a suitable thin blunt instrument  through the small hole shown in the guide. So don't be tempted to remove the box itself to unblock unless you really want to, it's not necessary IME. Just force it through, wash down with carb cleaner then change the oil. Although some older models do have an awful lot of gunk in there. Also don't be tempted to drill the small brass hole out to get into the blocked box, higher oil consumption will most likely result.

Thanks to YZ250 for his spare breather box and andyc  for his guide in straight six news.