Volkswagen Workshop Service and Repair Manuals > Golf Mk4 > Power unit | 4-cylinder injection engine (1.6 l roller rocker finger) | Mixture preparation system, electronic inj.,Gas | Checking components

Checking intake manifold change-over

Perform this test only if torque is insufficient, that is when elasticity or pulling power is inadequate.

Special tools and workshop equipment required

t	Hand vacuum pump -V.A.G 1390-

t	Vacuum tester -V.A.G 1368-

Test prerequisite

l	The variable intake manifold changeover valve -N156- is checked with vehicle diagnosis, testing and information system -VAS 5051B- in „Guided fault finding“.

Test procedure

If the variable intake manifold changeover valve -N156- is OK, perform the following tests:

–	Check that vacuum lines are connected correctly → Chapter.

–	Check vacuum hoses for porosity.

–	Test vacuum system for leaks.

Checking vacuum unit in upper part of intake manifold for leaks

–	Pull off vacuum hose to actuator for variable intake manifold changeover -arrow- on variable intake manifold changeover valve -N156--1-.

Note

The vacuum unit for intake manifold change-over is integrated in the intake manifold and not visible from the outside.

–	Connect hand vacuum pump -V.A.G 1390- to vacuum tester -V.A.G 1368- -connection B-.

–	Connect vacuum hose for vacuum unit to vacuum tester -V.A.G 1368- -connection A-.

–	Set vacuum tester to -A/B- position.

–	Operate hand vacuum pump -V.A.G 1390- several times. Create a vacuum of maximum 500 millibar.

–	Vacuum must not drop.

If vacuum drops:

–	Renew upper part of intake manifold → Chapter.

If pressure does not drop:

–	Check change-over mechanism in intake manifold for freedom of movement.

–	Remove upper part of intake manifold.

–	Repeat leakage test on vacuum unit. Check whether change-over flap moves.

If a fault is found:

–	Renew upper part of intake manifold → Chapter.

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