1081 VW Golf & Jetta

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Chapter 4 Part F:Fuel and exhaust systems - Digifant fuel injectionThe following information is a revision of, or supplementary to, that contained in Part B of this Chapter

Injection systemType . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DigifantApplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 litre (codes PBX and PF) engineSystem pressure at idle:

On . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Approximately 2.5 barOff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Approximately 3.0 bar

Idle speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 50 rpmCO content % . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 0.5Holding pressure (System off for 10 minutes) . . . . . . . . . . . . . . . . . . . . 2.0 bar minimum

Torque wrench settings Nm lbf ftThrottle valve housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 15Inlet manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 19Fuel pressure regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11Injector insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 15

Airflow meter - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Automatic air cleaner temperature control - testing . . . . . . . . . . . . . 4Control unit - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Fuel injectors - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Fuel pressure regulator - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Fuel pumps - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

General information and precautions . . . . . . . . . . . . . . . . . . . . . . . . 1Idle speed and mixture (CO content) - adjustment . . . . . . . . . . . . . . 2Idle speed stabilisation system - testing . . . . . . . . . . . . . . . . . . . . . . 3Overrun cut-off and full throttle enrichment - testing . . . . . . . . . . . . 11Throttle stop - adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Throttle valve switches - testing and adjustment . . . . . . . . . . . . . . . 5

4F1

Specifications

Contents

Easy, suitable fornovice with littleexperience

Fairly easy, suitablefor beginner withsome experience

Fairly difficult,suitable for competentDIY mechanic

Difficult, suitable forexperienced DIYmechanic

Very difficult,suitable for expert DIYor professional

Degrees of difficulty

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1 General information andprecautions

General informationThe Digifant fuel injection system is fitted to

the 1.8 litre (codes PB and PF) engine and is afully electronic and computerised version ofthe K-Jetronic system described in Part B ofthis Chapter.

The main components include acomputerised control unit, electronic injectorsand various sensors to monitor enginetemperature and speed, induction air flow andthrottle position. The control unit determinesthe opening period of the injectors and alsocontinuously adjusts ignition timing accordingto engine speed, load and temperature.

PrecautionsRefer to Sections 1 and 2 in Part B of this

Chapter whilst noting the following:

a) Take extra care to prevent dust and dirtentering system components

b) Do not use compressed air or fluffy clothsfor cleaning

c) Switch off the ignition beforedisconnecting any component wiring orwhen washing the engine

d) Boost-charging the battery is onlypermissible for one minute at 16.5 voltsmaximum

e) Disconnect both battery leads beforecarrying out any electric welding

2 Idle speed and mixture (COcontent) - adjustment 4

1 Run the engine until the oil temperature isat least 80C. This should correspond tonormal operating temperature.2 Switch off all electrical components,including the air conditioning, where fitted.Note that the radiator fan must be stationaryduring adjustment.3 For accurate adjustment, the throttle valveswitch and idling stabilisation control valvemust be functioning correctly and the ignitiontiming must be correct.4 With the engine stopped, connect atachometer to the engine. Plug one of theexhaust tailpipes and position the probe of anexhaust gas analyser in the remaining pipe.5 Disconnect the crankcase ventilation hosefrom the pressure regulating valve on thevalve cover and plug the hose.6 Run the engine at idle speed. Afterapproximately one minute, disconnect thewire from the temperature sender (seeillustration) and quickly increase the enginespeed to 3000 rpm three times.7 With the engine idling, check the idle speedand CO content. If necessary, adjust thescrews (see illustration). The CO adjustmentscrew is fitted with a tamperproof plug at thefactory. This plug should be prised out beforemaking an adjustment.8 Reconnect the temperature sender wireand again quickly increase the engine speedto 3000 rpm three times. With the engineidling, the idle speed and CO content shouldbe as specified. If necessary, make any smallcorrections required.9 Fit a new tamperproof plug.10 Reconnect the crankcase ventilationhose. Note that if this increases the COcontent, do not alter the adjustment. Thecause is fuel dilution of the engine oil due tofrequent stop/start use. A long fast drive

should reduce the CO content to the correctlevel. Alternatively, an oil change will achievethe same objective.

3 Idle speed stabilisationsystem - testing 2

1 Check that the stabilisation control valvebuzzes when the ignition is switched on. Ifnot, use an ohmmeter to check the continuityvalve after pulling off the connector (seeillustration).2 Run the engine until the oil temperature isat least 80C. This should correspond tonormal operating temperature.3 Connect a multi-meter to the stabilisationcontrol valve in series with the existing wiring.4 All electrical components must be switchedoff during the test and power steering (wherefitted) centralised.5 Run the engine at idle speed. Afterapproximately one minute, quickly increasethe engine speed to 3000 rpm three times. Atidling speed, the control current should beapproximately 420 30 mA and fluctuating.With the temperature sender plugdisconnected, the current should beapproximately 420 30 mA but constant.

4 Automatic air cleanertemperature control - testing 2

1 Disconnect the hose from the vacuum unitthen remove the air cleaner cover andelement.2 Check that the flap in the lower body isclosing the warm air inlet.3 Suck on the vacuum hose and check thatthe flap moves freely to close the cold air inlet.4 Flap operation may be checked with theengine idling by extending the vacuum hoseand positioning a thermometer by thetemperature regulator. Below 20C, the coldair inlet must be closed. Above 30C, thewarm air inlet must be closed. Between 20Cand 30C, the flap should be positionedmidway so that both inlets are open.5 Refit the air cleaner element and cover,then reconnect the hose.

5 Throttle valve switches -testing and adjustment 2

1 There are two throttle valve switches.Switch 1 monitors the throttle valve closedposition and switch 2 monitors the throttlevalve fully open position (see illustration).2 Disconnect the supply plug from switch 2and check that approximately 5 volts isavailable across the two terminals with theignition switched on. If not, check the wiringfrom the control unit.3 Connect an ohmmeter across the terminalsof switch 2, then slowly open the throttle valveuntil the switch points close. The gap at thethrottle lever stop must be 0.20 to 0.60 mmwhen the points close. If necessary, adjust theposition of switch 1.4 A piece of card marked with 10 is requiredto check switch 2. Attach the card to the firststage throttle valve shaft.

4F2 Fuel and exhaust systems - Digifant fuel injection

2.6 Crankcase ventilation pressure regulating valve (1) andtemperature sender (2)

2.7 Idle speed adjusting screw (1) and mixture (CO content)adjusting screw (2)

3.1 Idle speed stabilisation control valve(1)

1081 VW Golf & Jetta

5 Fully open the throttle and align a datumwith 0 on the card. Close the throttle byapproximately 20, then slowly open it untilswitch 2 points close. This should occur at10 2 before full throttle. If necessary,adjust the position of switch 2. Note that thethrottle valve lever roller must contact thesloping part of switch 2.

6 Throttle stop - adjustment 21 Throttle stop adjustment is initially set atthe factory and should not be tampered with.However, if it is accidentally disturbed,proceed as follows.2 Back off the adjustment screw until a gapexists between the carrier lever and stop lever(see illustration).3 Turn the adjustment screw until the twolevers just make contact, then continue to turnit a further half-turn. Tighten the locknut.4 After making an adjustment, readjust thethrottle valve switches, and the idle speed andmixture.

7 Fuel pressure regulator -testing 5

A pressure gauge and adapter is required forthis test. As these will not normally be availableto the home mechanic, it is recommended thata VW dealer carry out the test.

8 Fuel injectors - testing 31 Refer to Part B of this Chapter, Section 13,paragraphs 1 to 3, but in addition, carry outthe following electrical tests (see illustration).2 Disconnect the wiring plug from the conduitnext to the injectors and connect anohmmeter across the terminals on theconduit. The resistance of all four injectorsshould be 3.7 to 5.0 ohms. If any number ofinjectors are open-circuited, then theresistance will be as follows:One injector open-circuited - 5.0 to 6.7 ohmsTwo injectors open-circuited - 7.5 to 10.0ohmsThree injectors open-circuited - 15.0 to 20.0ohms

3 If necessary, prise off the conduit andcheck that each individual injector has aresistance of 15.0 to 20.0 ohms.4 Checking the injector spray patterns cannotbe performed as described in Part B of thisChapter, due to the position of the fueldistributor. However, the injectors may beremoved together with the fuel distributor andwiring conduit, and the engine turned on thestarter for a few seconds. Use a suitablecontainer to catch the fuel.

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1081 VW Golf & Jetta

5.1 Throttle valve housing components

A Front crankcase ventilationvalve

B Vacuum hose connectionfrom fuel pressureregulator

C Vacuum hose from aircleaner temperatureregulator

1 Air inlet hose2 Bolt3 Idle speed adjustment4 Throttle valve switch 15 Throttle valve switch 26 Throttle valve housing7 Gasket8 Bracket9 Bolt10 Inlet manifold

11 Vacuum hose to brakeservo unit

12 Idle speed stabilisationcontrol valve

13 Support14 Gasket15 Support16 Bolt17 Bolt18 Bracket

6.2 Throttle stop adjustment

Arrow indicates adjustment screw

1 Carrier lever 2 Stop lever

9 Airflow meter - testing 21 Disconnect the wiring plug from the airflowmeter (see illustration). 2 Connect an ohmmeter between terminals 1and 4 and check that the resistance of theinlet air temperature sender is as shown (seeillustration) according to the ambient airtemperature. 3 Connect the ohmmeter between terminals 3and 4 and check that the resistance of thepotentiometer is between 0.5 and 1.0 K ohms. 4 Connect the ohmmeter between terminals 2

and 3 and check that the resistance fluctuatesas the airflow meter plate is moved.

10 Control unit - testing 5The control unit is located on the left-hand

side of the bulkhead. The ignition must alwaysbe switched off before disconnecting theplug.

It is not possible to test the control unitwithout using the VW test appliances. If a faultis suspected, the unit should be taken to a VWdealer.

11 Overrun cut-off and fullthrottle enrichment - testing 2

1 Run the engine until the oil temperature isat least 80C (normal operating temperature)then let the engine idle.2 Manually close the full throttle valve switch2 and hold it closed.3 Open the throttle until the engine speed isapproximately 2000 rpm. Check that theengine speed surges, indicating that theoverrun cut-off is functioning.4 If the engine does not surge, disconnect thewiring from the temperature sender andconnect a bridging wire between the twocontacts on the plug.5 Repeat the procedure in paragraphs 2 and3. If the engine now surges, the temperaturesender is proved faulty. However, if it stillrefuses to surge, check the associated wiringand throttle valve switch 2.6 If no fault is found, renew the control unit.

12 Fuel pumps - testing 2Pre mid 19891 The main fuel pump is located in theaccumulator housing beneath the rear of thevehicle. An additional lift pump is located inthe fuel tank, together with the fuel gaugesender (see illustration).2 With the engine stopped, have an assistantswitch on the ignition. It should be possible tohear both pumps running for a short period. Ifnot, check fuse 5 for continuity and alsocheck all wiring connections.3 With the ignition on, disconnect each wireconnector from the pumps and check thatthere is a 12 volt supply by using a voltmeter. 4 Should there be no voltage at the pumpswith the ignition switched on, the fuel pumprelay (No 2 on fusebox) may be faulty. This isbest checked by substituting a new relay.

From mid 19895 From mid 1989, certain models fitted withthe Digifant system are fitted with a single fuelpump in the fuel tank rather than the previousarrangement described above. The pump canbe tested in the same manner as thatdescribed for the previously fitted in-tankdual pump.6 The fuel pump can be removed in a similarmanner to that described for the fuel gaugesender unit in Part A of this Chapter, Section8.

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1081 VW Golf & Jetta

8.1 Fuel injectors and pressure regulator components

A Crankcase, ventilationhose

B Vacuum hose1 Fuel pressure regulator2 Bracket3 Bolt4 Fuel return hose (blue)

5 Fuel supply hose (black)6 Bolt7 Bracket8 Crankcase ventilation

pressure regulator valve9 Connector10 Temperature sender

11 O-ring12 Fuel distributor13 Wiring conduit14 Clip15 Plug16 Injector17 Insert

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1081 VW Golf & Jetta

9.1 Airflow meter components

1 Air cleanerelement

2 Cover3 Bolt4 Seal5 Airflow meter6 Connector7 Tamperproof plug8 Mixture (CO

content)adjustment screw

9 O-ring10 Clip11 Air inlet hose12 Plate13 Seal14 Retaining ring15 Air cleaner body16 Rubber washer17 Temperature

regulator18 Warm air hose

9.2 Inlet air temperature sender resistance graph

12.1 Fuel pump and filter components

1 Bracket2 Rubber mounting3 Nut4 Fuel supply to fuel distributor5 Fuel filter6 Pump accumulator7 Strainer8 Fuel pump9 O-ring10 Retainer11 From fuel lift pump in fuel tank12 Return to fuel tank13 Return from pressure regulator14 Adapter

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1081 VW Golf & Jetta

Notes