Cars / e34 / Engine / S38 ITB Synchronization

S38 ITB Synchronization

Article by: Igor Kostenuk

Article applies to: all BMW models with the S38 Motorsport engine.

I decided to pull this job on my M5 a couple days ago and document it as much as I could.

This job requires a couple of special tools which I will list and other things that need to be done prior to doing this job in order to do it correctly.

PRIOR to adjustment:
All 24 valves must be adjusted to spec (0.28 to 0.33mm)
All ignition components in full working order ( Cap and rotor, coil, spark plugs, wires and crank position sensor)
All vacuum lines under the Intake Plenum must be fresh, can’t have vacuum leaks.
All vacuum related rubber o-rings must be replaced.

Tools Needed
Carbtune tool http://www.carbtune.com/
Vernier Calliper
Feeler gauges
10mm socket
8mm socket
7mm socket
Screw drivers

Parts needed
Brass screw o-rings 17211742635 x6
Throttle body to plenum o-rings 11611305124 x6
Vacuum hose, 1-2 meters of it.

Procedure

Remove the intake plenum and replace every vacuum line in your sight:

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Remove the TB shocks using an 8mm socket or wrench:

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This is what they look like:

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Adjust the shock according to BMW specs:

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Use a vernier calliper to adjust to 98mm:

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Clean up the little shocks, use a drill with a wire brush bit, treat with oil after cleaning them.

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Next step is to adjust the ITB throttle valves:

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Adjust by BMW spec (top 21.7mm, bottom 22.7mm)

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Assemble everything back, use new o-rings between the ITBs and and Intake plenum tubing (sorry forgot to take pics of that)

O-rings p/n#: 11611305124. Assemble all the ITB components back.

Now start removing the brass screws, use 7mm socket:

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Remove all of them, be careful, if they haven’t been out of the in a while, you can strip or break one, they are made from brass, very soft material.

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This is what they look like out:

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Clean out the holes as much as you can:

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I used a pick and 600 grit sand paper:

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Remove old o-rings:

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Clean up the brass screws using a drill and a wire brush bit.

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New O-rings:

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Install new o-rings:

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Screw them back into the ITB’s:

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Tighten to the end and do ONE full turn back (360 degrees):

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Now I’m going to replace the spark plugs and the ignition coil (mine were due).

After this I will start balancing the ITB’s.

NEW coil:

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New spark plugs:

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Old vs. New:

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Set spark plug gap:

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Now the Balancing begins:

Connect carbtune vacuum lines to the ITB ports, you can only do 4 ITB’s at a time with this tool, so leave the other two plugs in on cylinder 5 and 6.

After, just move two vacuum lines to cylinders 5 and 6 and plug cyl 1 and 2. Use cylinder 3 and 4 for reference.

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Make sure the tool stands vertically.

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ENGINE MUST BE AT OPERATING TEMPERATURE, YOU CANNOT DO THIS ON A COLD ENGINE

Start the engine and observe your carbtune. Use a 7mm socket to adjust. Tighten in increase vacuum, loosen to decrease vacuum.

BMW says they should all be around 22.7 in Hg. I wouldn’t worry about that too much, make sure the readings are more less on the same line and the idle is from 850-950rpm.

This is how it works, the higher your vacuum is, the lower your idle speed will be, the lower your vacuum is, the higher the idle speed will be.

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And DONE.

Bonus pic

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