Maximum Boost Pressure

Run hose of pressure reading equipment (83 93 514) from passenger compartment to engine compartment. Position pressure checking gauge vertically (to avoid erroneous readings). Connect hose of pressure reading equipment to connection of vacuum hoses placed beside expansion tank.
Tilt rear seat cushion forward and detach electrical wiring from control unit. Connect test wiring harness (83 93 548) with service box between normal harness connector for control unit and control unit itself.
Set knock detector switch on service box to OFF position. This switching off has to be made to prevent knock detector from varying boost while measurements are being taken. Depending on type of fuel in tank, engine may knock continually while measurements are being taken. Engine should be at normal operating temperature.
CAUTION: Checking maximum boost pressure in a road test must be performed as quickly as possible (approximately 3-5 seconds) to avoid abnormally high temperatures building up in brake linings.

Fig 1: View of APC System

NOTE: Car should be driven at least .6 of a mile between each test and after testing is completed in order to allow brake linings to cool.
On cars with manual transmissions, start test by driving car in 3rd gear at an engine speed lower than 1500 RPM. On cars with automatic transmissions, start test by driving car with gear selector in position "1" at an engine speed lower than 1500 RPM.
Depress accelerator pedal to floor. When engine speed approaches 3,000 RPM, apply brakes (while keeping accelerator pedal pressed to floor) so engine is held under full load at 3,000 RPM. Read boost pressure from pressure gauge.
NOTE: A boost pressure surge may be noted when engine is accelerated to maximum, i.e. boost pressure will momentarily exceed pre-set maximum figure when accelerator is floored.
Once stabilized, pressure reading should be (.6 bar). If boost pressure is correct, remove testing equipment. If boost pressure is incorrect, faulty boost pressure regulator valve, sticking diaphragm unit pushrod bushing, or blocked orifice in solenoid valve hose connection to turbocharger may be the problem.