Checking overrun boost — VW

FB FH FK FN FP FT FV HN JB GY HM HV AJD
(Vehicle with manual gearbox only)

Minimum engine oil temperature 60 °C.
Choke valve fully open.
Ignition off.

Connect up ignition tester V.A.G1367 with clip-on trigger V.A.G 1367/8 or ignition tester V.A.G 1767.
Start engine, increase speed to 4000 rpm and release throttle lever. The engine speed must drop off slowly to approx. 1700...1800 rpm, dwell at this level and then drop off more quickly to idling speed. If not, check following functions/settings:
Throttle valve positioner/overrun mixture valve =>page
22-85
Control valve =>page
22-90
.
Voltage supply for control valve (control unit) =>page
22-87
.
Retard valve /with throttle valve positioner only): vacuum connections =>page
22-93
.

Checking overrun mixture valve

(vehicle with manual gearbox a 07.84)

Connect vacuum pump V.A.G 1390 and vacuum tester V.A.G 1368 to connection -A- of overrun mixture valve.
Start engine and let it idle.
Used vacuum pump to generate vacuum.
At 640...680 mbar the overrun mixture valve must open and there must be a noticeable increase in idling speed (100...300 rpm). If necessary, adjust overrun mixture valve. to do so, loosen lock nut -B- and turn vacuum connection -A-.

Checking and adjusting throttle valve positioner

(including vacuum unit leak test)

Minimum engine oil temperature 60 °C.
Choke valve fully open (starter cable fully in).
Idle adjustment OK; checking =>page
22-72

Connect up ignition tester V.A.G 1367 with clip-on trigger V.A.G 1367/8 or ignition tester V.A.G 1767.

Connect up vacuum tester V.A.G 1368 and vacuum pump V.A.G 1390 to vacuum unit.
Switch vacuum tester to throughflow.
Use vacuum pump to generate approx. 300 mbar.

The throttle valve positioner must open the throttle valve slightly; if necessary, check vacuum unit for leaks as follow.

Set vacuum tester such that vacuum is held on vacuum unit end.
Set vacuum on tester to 200 mbar, The vacuum may drop off by max. 10% in one minute. Otherwise there is a leak in the vacuum unit/hose.

Start engine and check engine speed. Adjust if necessary with screw -1-.
Specification: 1200 ± 500 rpm.

Checking control unit and voltage supply for the overrun boost control valve

Minimum engine oil temperature 60 °C.
Choke valve fully open (choke cable fully in).

Connect up ignition tester V.A.G 1367 with clip-on trigger V.A.G 1367/8 or ignition tester V.A.G 1767.

Pull plug off control valve and use auxiliary leads form V.A.G 1594 to connect up hand multimeter V.A.G 1526 for voltage measurement to both plug contacts.
Start engine and let it idle.
Specification: approx. battery voltage
If necessary, located and eliminate open circuit in wiring using CFD:
Slow increase speed/let it drop off and determine switching speeds of control unit.

Specifications for increasing speed:
with overrun mixture valve
above 1750 rpm · = · 0 volts
with throttle valve positioner
above 1900 rpm · = · 0 volts

Specifications for decreasing speed:
with overrun mixture valve
below 1500 rpm · = · approx. battery voltage
with throttle valve positioner
below 1750 rpm · = · approx. battery voltage

Renew control unit if the specifications are not attained.

Checking control valve

(for overrun boost with throttle valve positioner)

Voltage supply Ok; checking =>page
22-87

Remove air cleaner.
Start engine and let it idle.
Pull plug off control valve.
Pull vacuum hose (control valve/retard valve) off retard valve.
Pull vacuum hose (control valve/servo unit line) off servo unit line.
Pull vacuum hose (control valve/carburettor) off T piece and blow into hose. The valve must be tight; otherwise the valve is defective (renew) or the vacuum hose is leaking.
Connect plug to control valve and simultaneously blow intro vacuum hose (control valve/carburettor).
The valve must be heard to click and open up. If not, control valve is defective (renew) or vacuum connections/hoses are clogged.

Note:

If the valve is blown into from the retard valve end, the valve must be open both with and without voltage supply. If not, renew valve.

Checking control valve

(for overrun boost with overrun mixture valve)

Voltage supply Ok; checking =>page
22-87

Remove air cleaner.
Start engine and let it idle.
Pull plug off control valve.
Pull valve hose (control valve/overrun mixture valve) off overrun mixture valve.
Pull vacuum hose (control valve/servo unit line) off servo unit line and blow into hose. The valve must be open. If not, valve is defective (renew) or vacuum hose is clogged.

Attach plug to control valve and simultaneously blow into vacuum hose (control valve/servo unit line). The valve must be heard to click and be sealed off. If not, control valve is defective (renew) or vacuum connections/hoses are leaking.

Note:

If the valve is blow into from the overrun mixture valve and, the valve must be open both with and without voltage supply. If not, valve is defective (renew) or vent cap at 3rd vacuum connection is clogged.