General information and precautions

Fuel and exhaust systems - Mono Jetronic fuel injection / General information and precautions

General information
The Mono-Jetronic central fuel injection system is fitted to the 1.8 litre (code RP) engine. It is a simplified method of fuel injection (see illustrations).

1.0a Mono-Jetronic system component location

1 Electronic Control unit (ECU) 2 Connector (throttle valve positioner and idle switch) 3 Throttle damper
4 Connector (injector and air intake temperature sender) 5 Throttle valve positioner and idle switch 6 Intake air pre-heater temperature regulator 7 Injector and air temperature sender 8 Fuel pressure regulator 9 Inlet manifold pre-heater 10 Injection timing vacuum control valve 11 Injector
12 Throttle valve potentiometer 13 Water separator (throttle valve potentiometer) 14 Self diagnosis fault warning lamp 15 Lambda probe connector 16 Activated charcoal filter solenoid valve 17 Activated charcoal filter solenoid valve 18 Injector series resistor 19 Thermoswitch for manifold pre-heater 20 Coolant temperature sender 21 Self diagnosis plug

1.0b Mono-Jetronic system inlet manifold and associated components

1 Warm air deflector 2 Nut
3 Flange
4 Bolt
5 Bracket
6 Lambda probe
7 Bolt
8 Inlet manifold
9 O-ring
10 Gasket
11 Cap
12 CO measuring pipe
13 Spacer
14 Coolant hose connection 15 Vacuum connection
16 O-ring
17 Thermoswitch (red) for manifold pre-heater – from 8/1988 18 Coolant temperature sender (blue) 19 Retainer spring
20 Thermoswitch (red) for manifold pre-heater – up to 7/1988 21 Coolant sender unit
22 Inlet manifold pre-heater 23 Screw
24 Connector

Fuel is injected into the inlet manifold by a single solenoid valve (fuel injector) mounted centrally in the top of the injector unit housing.

The length of time for which the injector remains open determines the quantity of fuel reaching the cylinders for combustion. The electrical signals which determine the fuel injector opening duration are calculated by the Electronic Control Unit (ECU) from information supplied by its network of sensors. Fuel pressure is regulated mechanically.

The signals fed to the ECU include the following:
a) The engine coolant temperature b) The engine speed and crankshaft position - from the distributor
c) The position of the throttle valve plate - from the throttle position sensor d) The oxygen content in the exhaust gases - via a sensor (Lambda probe) in the exhaust manifold
Using the information gathered from the various sensors, the ECU sends out signals to control the system actuators as required.

The ECU also has a diagnostic function which can be used in conjunction with special VW test equipment for fault diagnosis. With the exception of basic checks to ensure that all relevant wiring and hoses are in good condition and securely connected, fault diagnosis should be entrusted to a VW dealer.

Basic testing can be carried out on the system components covered in the following text. More detailed testing can be carried out by using specialised equipment but this must be entrusted to a VW dealer.

Precautions
Refer to Sections 1 and 2 in Part B of this Chapter.