Volkswagen Golf/Jetta/Cabriole 1990-1999

CIS-E Motronic



Click image to see an enlarged view

Fig. CIS injection unit-Fox

Click image to see an enlarged view

Fig. CIS-E (electronic) fuel system

The CIS-E Motronic system used on the 16V engine is a highly developed and electronically controlled version of the original Bosch® Continuous Injection System (CIS). The main components are the fuel distributor, mechanical injectors and a fuel pump.

The fuel pump is mounted in a reservoir under the vehicle, along with the filter and fuel accumulator. The reservoir holds about 1 liter of fuel and is supplied by a small transfer pump in the fuel tank. The transfer pump is part of the fuel gauge sending unit assembly but it can be replaced separately.

The fuel distributor used in the Motronic system is very different from that used in earlier CIS systems. The unit is made of aluminum and is slightly smaller. It is still divided into an upper and a lower chamber but the pressure difference between chambers is not constant. A differential pressure regulator mounted on the side controls the pressure in the lower chamber which ultimately controls the fuel flow to the injectors. Control plunger movement controls the amount of fuel supplied to the upper chamber. When the engine is not running, the control plunger rests on an O-ring and there is some free-play between the plunger and air flow sensor arm. If the fuel distributor is replaced, the plunger free-play must be adjusted.

The fuel distributor is mounted on the mechanical air mass sensor. As air flows into the air cleaner and up through the sensor assembly, the air pushes the sensor plate up, which lifts up the fuel distributor plunger. When the engine is not running, the arm that the plate is bolted to rests on a spring. This allows some opposite movement of the plate if the engine back fires. There is no service procedure that requires disassembly of the air flow sensor. If the plate is removed, a special tool is required to center the plate in the bore.

The fuel injectors are purely mechanical and open at 54-70 psi (3.7-4.8 BAR) fuel line pressure. All injectors are open when the engine is running, injecting fuel to the intake ports continuously. They are mounted into plastic inserts that are threaded into the intake manifold. An O-ring is used to hold the injector in place and at the same time to seal the insert. Injectors can be removed from the insert without disconnecting the fuel line. The cold start injector is mounted at the flywheel end of the intake manifold. It is a simple solenoid valve with a spray nozzle tip. During starter operation, the control unit operates this injector when engine depending on coolant temperature is below 86°F (30°C).

Other components in the Motronic system include the oxygen sensor, a coolant temperature sensor, a position sensor in the air flow sensor, two throttle position switches, the idle air stabilizer valve, and the fuel system pressure regulator. The function and testing of all these items is described in , Electronic Engine Controls.

Never smoke when working around gasoline! Avoid all sources of sparks or ignition. Gasoline vapors are EXTREMELY volatile!

Most of the following procedures will produce fuel vapors. Make sure there is proper ventilation and take the appropriate fire safety precautions.