Fuel Injection System - Bosch Cis Audi 4000 S Quattro

DESCRIPTION

Bosch Continuous Injection System (CIS) is a mechanical fuel injection system which uses airflow sensor assembly connected to fuel distributor to control injection quantity.

Lambda is a feedback control system capable of continuously measuring and correcting air/fuel ratios. Combination of 2 systems allows for both economy and performance with minimal exhaust emissions. (Scheme 12)

Bosch CIS Lambda Fuel Injection System Diagram This illustration is typical of all models. Specific details may vary. Scheme 12

System consists of mixture control unit (airflow sensor and fuel distributor), control pressure (warm-up) regulator, auxiliary air regulator, cold start valve, thermo time switch, fuel injectors, fuel pump, filter, oxygen (O2) sensor, electronic control unit (ECU), frequency valve and catalytic converter.

Some models use additional components, such as thermo vacuum valve, hot start pulse relay or constant idle speed control system.

MIXTURE CONTROL UNIT

Airflow sensor housing contains sensor plate which moves in cone-shaped venturi. All engine intake air is drawn past sensor plate. Sensor plate, and attached hinged lever, moves with air drawn into engine.

Movement of sensor plate lever changes position of control plunger in fuel distributor. Control plunger is used to meter amount of fuel injected into each cylinder. Movement of plate is controlled by airflow, cone shape of venturi, counterbalance weight and fuel pressure.

Note. Air flows UP through sensor housing on most inline engines, and DOWN through sensor housing on V6, V8 and turbocharged engines. Direction of airflow is changed for manufacturer's convenience in routing airflow.

Fuel distribution can be equal only if pressure to each injector is equal. Pressure regulating valves in fuel distributor equalize system pressure. These valves are adjusted during assembly of fuel distributor and cannot be adjusted in service.

CONTROL PRESSURE REGULATOR

Control pressure regulator (or warm-up regulator) modulates system fuel pressure before it goes to top of plunger in fuel distributor. (Scheme 13)

During cold start operation, reduced control pressure allows plate to open farther with same airflow. This supplies more fuel (richer mixture) to injectors until normal operating temperature is reached. As engine warms up, control pressure regulator increases control pressure, causing leaner air/fuel mixture.

Bi-metallic strip in control pressure regulator reduces spring pressure on control diaphragm. Strip is heated by electric coil. As strip heats up, it will bend and allow increased spring pressure on control diaphragm. This will increase control pressure.

Poor electrical connections will cause warm-up function of regulator to cease operation. Some regulators have altitude compensation function that changes with barometric pressure.

Control Pressure Regulator Pressure-compensated type is shown; all types are similar. Scheme 13

AUXILIARY AIR REGULATOR

During cold start operation, auxiliary air regulator provides additional air to engine to increase idle speed. It allows intake air to by-pass throttle plates which are closed at idle.

Heating coil in regulator is connected to fuel pump circuit. As coil warms up, air passage gradually closes. Regulator is calibrated to maintain smooth idle without major engine speed changes as engine is warming up.

COLD START VALVE

Cold start valve is mounted on intake manifold and sprays fuel during starting. It provides additional enrichment so engine will start easily. Valve is powered through starter circuit and grounded through thermo time switch. It operates only while cold engine is being cranked.

THERMO TIME SWITCH & HOT START PULSE RELAY

Thermo time switch provides ground for cold start valve. It is affected by engine temperature and starter current. Depending on engine coolant temperature, switch will take from 3-10 seconds to open. Injection through cold start valve will stop when thermo time switch opens.

Some models use hot start pulse relay to improve hot starting. While starter is being operated on cold engine, pulse relay allows cold start valve to spray small amounts of fuel at regular intervals after thermo time switch open. On hot engines, pulse relay allows cold start valve to spray fuel after 2 seconds of starter operation, shut off, then spray periodically until engine starts.

FUEL INJECTORS

Fuel injectors in CIS system open at pre-set pressure. Fuel is always present in lines between fuel distributor and injectors to ensure good starting. As pressure from fuel distributor increases (when engine is started), valves open and spray constantly. Amount of fuel injected will be determined by position of control plunger in fuel distributor. (Scheme 14)

Bosch CIS Lambda Fuel Injector Pin in injector vibrates to atomize fuel. Scheme 14

FUEL PUMP

Electric fuel pump is used to provide fuel pressure of 60-80 psi (4.2-5.6 kg/cm 2 ). To aid in starting, check valve in pump maintains pressure in lines when engine is not running. Fuel accumulator and line pressure regulator "O" ring also act to hold pressure in system.

Fuel pump is controlled by relay to prevent it from continuing to operate if engine stalls. It can be wired in several ways. Two common circuits use switch on airflow sensor or coil energized by ignition system. When testing system, fuel pump relay must be by-passed.

O2 SENSOR

O2 sensor is located in exhaust manifold and measures amount of unburned O2 in exhaust gas. If O2 is low (rich mixture), higher voltage will be generated by sensor. If O2 is high (lean mixture), lower voltage will be generated. Voltage signal from O2 sensor is sent to ECU which controls fuel mixture through frequency valve.

ECU & FREQUENCY VALVE

ECU continually corrects air/fuel mixture, based on signals from O2 sensor. ECU sends signals to frequency valve, which is located in fuel line between upper and lower halves of fuel distributor. Frequency valve operates at constant frequency (70 Hz) as soon as engine is running.

When frequency valve is closed, fuel pressure to injectors is determined by spring in each pressure regulating valve. When frequency valve is open, fuel pressure decreases in lower half of fuel distributor, tension on spring is relieved, and more fuel is directed to cylinders. (Scheme 15)

ECU grounds connection for frequency valve in different length pulses. This will open and close valve to ensure continuous regulation of fuel mixture. When engine is cold, ratio of valve open to valve closed is about 60/40.

After engine warms up, voltage produced by O2 sensor determines amount of time frequency valve must be open or closed. This ratio can be read with special tester or with dwell meter (on most models). Dwell reading of 45° indicates ratio of 50% open, 50% closed.

Effect Of Frequency Valve On Fuel Distributor. Scheme 15

CATALYTIC CONVERTER

CIS Lambda systems can control air/fuel ratios within .02%. This close regulation allows use of 3-way catalyst that can decrease NOx, HC, and CO emissions. Converter can be damaged by improper adjustment of system or by use of leaded fuels.

ELECTRONIC IDLE SPEED CONTROL SYSTEMS

This system maintains constant idle speed by varying amount of air by-passing throttle valve through air control valve. Air control valve is operated by idle speed ECU which receives engine information from throttle switch, coolant temperature sensor, and ignition coil.

TESTING

Note. Testing procedures described below will apply to all models using CIS Lambda system unless otherwise noted. Not all models will use all components.

Scheme 16

1. All CIS systems are very sensitive to air leaks. Check condition of rubber boots, hoses and gaskets. Other areas of air leakage are injector "O" rings, cold start valve, oil filler cap and dipstick.
2. Install pressure gauge to perform fuel pressure tests. On all models, pressure gauge is installed in line between control pressure regulator and fuel distributor. (Scheme 16) (Scheme 16): Pressure Gauge Installation Bleed pressure gauge by opening and closing valve several times.
3. To operate fuel pump with engine not running, disconnect fuel pump relay from relay panel on Audi models. Insert jumper wire into sockets that correspond to terminals 30 and 87 on relay.
4. To operate fuel pump turn ignition on. Place pressure gauge as low as possible in engine compartment, then open and close valve 5 times to bleed gauge. Place valve in open position and hang in convenient location. Turn pump off.

Scheme 17

Scheme 18

1. Remove rubber bellows above airflow sensor plate. Unplug electrical connectors on auxiliary air regulator and control pressure regulator. Operate fuel pump for 10 seconds to build up control pressure. (Scheme 17): Removing Fuel Distributor Control Plunger DO NOT allow control plunger to drop from fuel distributor.
2. Lift sensor plate slowly with magnet or pliers. Use care to avoid damage to sensor plate or venturi surfaces. Resistance due to control plunger pressure should be felt through entire lift. Release plate and allow it to return to rest position slowly. Lever and control plunger should follow. (Scheme 18)
3. Lift plate and return it rapidly to rest position. Plunger should be heard hitting lever as it moves slowly to rest position. If not, control plunger is sticking. Remove 3 screws from fuel distributor and lift off of airflow sensor housing. Be careful not to drop control plunger. (Scheme 17) (Scheme 18): Checking Sensor Plate Operation & Adjustment
4. Clean plunger in gasoline. Remove any deposits with finger nail; DO NOT use tools. Slide plunger in and out while turning it. If any sticking or binding is felt, replace fuel distributor.
5. Reinstall fuel distributor. Plate should be centered in housing. If not, loosen center bolt and align plate with 0.004" (.1 mm) feeler gauge at 4 points around rim. Using Loctite, install and tighten bolt.
6. Check airflow sensor plate height adjustment. Plate should be even with bottom rim or 0.02" (0.5 mm) lower. If not, bend spring clip or reposition stop pin (tap lightly with punch) to set plate height. (Scheme 18)

CONTROL PRESSURE TEST (COLD ENGINE)

1. Testing must be done on cold engine. Unplug electrical connectors at auxiliary air valve and control pressure regulator. Place valve on pressure gauge in open position and operate fuel pump. Check control pressure.
2. Reading should fall in shaded area of graph. Check ambient air temperature and read correct area of graph. (Scheme 19) If control pressure is not correct, retest with new control pressure regulator. Control pressure regulator cannot be adjusted.

Note. Some control pressure regulators have atmospheric pressure compensation. If so, fuel pressures will vary depending upon barometric pressure.

Control Pressure Test (Cold Engine) Graphs. Scheme 19

CONTROL PRESSURE TEST (WARM ENGINE)

1. Connect plug to control pressure regulator. Leave auxiliary air valve and airflow sensor (if equipped) plugs disconnected. Place valve for pressure gauge in open position and operate fuel pump.
2. After about 5 minutes, control pressure should rise to specified level. See CIS (LAMBDA) FUEL PRESSURES table. On models with vacuum hose connected to control pressure regulator, leave hose connected to read pressure.
3. Start engine and allow to idle. Pressure should remain same or rise slightly. On models with control pressure regulator vacuum line, remove and plug hose. Pressure should drop.
4. If pressure does not reach level specified, disconnect plug at control pressure regulator. Check for voltage across terminals with test lamp or voltmeter. At least 11.5 volts should be present. If not, check wiring. If voltage is present and pressure not correct, replace control pressure regulator.

CIS (LAMBDA) FUEL PRESSURES

SYSTEM (LINE) PRESSURE TEST

1. Close valve on pressure gauge. With engine off, operate fuel pump. Pressure should rise to level specified. See «CIS (LAMBDA) FUEL PRESSURES»(/audi/4000-s-quattro/1985-1985/remont/testing-diagnostics/#fuel-injection-system-bosch-cis) table. If pressure is too low, check fuel pump output.
2. Disconnect fuel return line from fuel distributor and run hose from fuel distributor to container. Operate fuel pump and measure output after 30 seconds. See FUEL PUMP OUTPUT SPECIFICATIONS table. If not as specified, check fuel lines, filter, accumulator and pump. FUEL PUMP OUTPUT SPECIFICATIONS Application 30 Sec. Flow Rate: Qts. (L) Audi.80 (.76)
3. If pressure is too high, check for kinked or blocked fuel return line. If lines are clear, system pressure regulator must be adjusted. Turn pump off, loosen return line fitting, and relieve pressure.
4. Loosen line pressure regulator nut. Remove shims, spring(s) and plunger. Raise system pressure by adding shims; lower pressure by removing shims. Be sure "O" rings are in good condition. If piston is scored or damaged, complete fuel distributor must be replaced. (Scheme 20)

Line Pressure Regulator Replace complete fuel distributor if piston is damaged. Scheme 20

RESIDUAL PRESSURE & INTERNAL LEAK TESTS

1. After correct warm engine control pressure has been obtained, stop fuel pump and note pressure drop. Pressure gauge valve should be in open position. Minimum pressure after 20 minutes must be as specified. See «CIS (LAMBDA) FUEL PRESSURES»(/audi/4000-s-quattro/1985-1985/remont/testing-diagnostics/#fuel-injection-system-bosch-cis) table.
2. If pressure drops too rapidly, run pump again and close valve. Stop pump and observe pressure. If values are now correct, control pressure regulator is faulty and must be replaced.
3. If pressure still drops, check all connections, fuel pump check valve, cold start valve and fuel injectors.

COLD START VALVE, THERMO TIME SWITCH & PULSE RELAY

1. If engine coolant is below 85°F (30°C), disconnect plug on cold start valve and connect test lamp across terminals. Remove coil high tension wire to prevent starting. Operate starter.
2. On models without pulse relay, test lamp will light for several seconds, then go out. On models with pulse relay, lamp will continue to flash off and on. If lamp does not light, test thermo time switch for continuity below opening temperature. If good, check wiring to starter terminal.
3. Remove cold start valve from manifold but leave fuel line connected. Place valve in container. (Scheme 21) Connect jumper wire from one terminal to ground, and from other terminal of cold start valve to switch. Other side of switch should be connected to source of battery voltage. Operate fuel pump.
4. Turn switch on. Cold start injector should spray. Turn switch off, but leave fuel pump running. Injector should stop spraying. Wipe off nozzle. No drops should form within 1 minute with pump running. Replace cold start valve that is faulty. Install original valve if good, making sure that "O" ring is properly positioned.
5. On models without hot start pulse relay, test lamp will light for several seconds, then go out. On models with relay, lamp will continue to flash off and on. If lamp does not light, test thermo time switch for continuity below opening temperature. If good, check wiring to starter terminal.
6. Remove cold start valve from manifold but leave fuel line connected. Place valve in container. (Scheme 21) Connect jumper wire from one terminal to ground, and from other terminal of cold start valve to switch. Other side of switch should be connected to source of battery voltage. Operate fuel pump.
7. Turn switch on. Cold start injector should spray. Turn switch off, but leave fuel pump running. Injector should not spray. Wipe off nozzle and check for leakage. With pump running, no drops should form within one minute. Replace cold start valve if faulty. Install original valve if good, making sure that "O" ring is properly positioned.

Testing Cold Start Injector Valve Valve should not drip after shutting off. Scheme 21

1. Remove injectors but leave hoses connected. Place injectors in individual measuring containers. With sensor plate in idle position, connect jumper wire in place of fuel pump relay.
2. Disconnect fuel pump when measuring container with highest level of fuel reaches specified capacity. See «AUDI FUEL INJECTION QUANTITY»(/audi/4000-s-quattro/1985-1985/remont/testing-diagnostics/#fuel-injection-system-bosch-cis) table.
3. Compare amounts of fuel in measuring containers. Fuel quantity should not vary outside specified range. Repeat test with sensor plate in full throttle position.

AUDI FUEL INJECTION QUANTITY

Testing Fuel Injectors Replace injectors if opening pressure is not in limits. Scheme 22

1. Disconnect hoses from auxiliary air regulator. Use mirror and small flashlight to inspect valve opening. (Scheme 23) At room temperature, valve should be slightly open. Valve should close within 5 minutes after cold engine starts.
2. If valve does not operate properly, check for power at connector with engine running. Connect test lamp across connector terminals. If lamp does not light, check fuse and wiring.
3. If lamp lights, check resistance of auxiliary air regulator. If no resistance is measured, regulator is defective. Ensure electrical connections are tight and terminals are clean, prior to measuring resistance.

Checking Auxiliary Air Regulator Operation Valve should close after engine is running for 5 minutes. Scheme 23

PREPARATION FOR CHECKS

1. Frequency valve is operated by pulsating voltage from ECU. By measuring this signal, mixture function of system can be tested and changed. High-quality dwell meter may be used on all other models.
2. Connect dwell meter to 2-wire testing connector. Connector is located behind throttle valve housing (Blue/White wire) on Audi.
3. The color-coded wire should be connected to positive (+) lead of dwell meter. Other wire in connector is ground and should be connected to negative (-) lead of dwell meter. Set dwell meter on 4-cylinder scale. Start engine and run until warm.

Scheme 24

1. Remove fuel pump relay and connect jumper wire across sockets corresponding to terminals 30 and 87. If equipped, remove plug at airflow sensor. Turn ignition on.
2. Frequency valve should operate, making buzzing noise. Dwell meter should indicate 45-65°. Disconnect wire from O2 sensor and touch wire end to ground. Readings on dwell meter should rise. Ground one end of 1.5 volt flashlight battery, and touch positive end to sensor wire. Readings should drop to less than 15°.
3. On models with throttle enrichment switch, operate throttle. Readings should be higher at idle or wide open throttle. (Scheme 24)
4. If engine is cold, enrichment switches will be closed. Disconnect lead at temperature sender. Readings should drop slightly. If engine is hot, connect temperature sender lead to ground. Reading should rise.
5. If starter enrichment relay is used, disconnect high tension lead at coil and crank engine. Readings should rise above normal level. If vacuum switches are used, apply vacuum to switch and note readings. Level should be higher with switch closed, and lower with switch open.
6. Connect O2 sensor and start engine. With cold engine, dwell reading should be stable. When engine warms up, meter needle should fluctuate 10-20°. It may be necessary to run engine faster than idle to heat O2 sensor and cause needle fluctuation. (Scheme 24): Bosch CIS Lambda ECU Wiring Diagram
7. Connect CO meter to exhaust test point. With O2 sensor disconnected, reading should be stable on dwell meter. Note CO% reading. With sensor lead grounded, reading should rise and CO% increase. With lead connected to flashlight battery, reading and CO% should decrease.
8. If dwell reading does not rise with sensor grounded, check sensor wiring. See ELECTRICAL TESTING. If wiring is good, replace control unit. If dwell rises, but CO% does not, check frequency valve and wiring. See ELECTRICAL TESTING. Replace if necessary.
9. If dwell does not decrease with battery connected to sensor lead, check sensor wiring and replace control unit if wires are good. If dwell decreases but CO% does not, check frequency valve wiring and replace valve if wiring is good.
10. Adjust CO% to rich level (3%) with O2 sensor still disconnected. Reconnect sensor. Reading should drop at least 1%. If not, replace O2 sensor.

ELECTRICAL TESTING

Note. ECU is located behind right front kick panel on Audi.

1. Locate ECU and press locking tabs back to disconnect connector. All connectors are wired with pin numbers in same location. Use volt-ohmmeter for testing.
2. Refer to wiring diagram for pin locations. With fuel pump relay jumper wire in place, turn ignition on and check for battery voltage at terminals 8 and 15. Connect ground lead of voltmeter to terminals 5 and 16 while checking for battery voltage to ensure these wires make good ground connection.
3. If battery voltage is not available at terminal 8, check Lambda and fuel pump relays. If there is no voltage at 15, check frequency valve connector. One wire should have battery voltage; other wire should have continuity to terminal 15. Frequency valve should have 2-3 ohms resistance. Repair or replace as necessary.
4. Disconnect O2 sensor and check for continuity between sensor lead and terminal 2. No continuity should exist between ground and lead wire.
5. All models use switches for enrichment signal. All switches provide continuity to ground when switch is closed. Actuate throttle to test throttle valve switches.
6. Thermal switches can be checked by removing switch and heating in water. Repair wiring or replace switches as necessary.
7. After testing is completed, reconnect ECU, O2 sensor and all switches. Remove fuel pump relay jumper wire and testing equipment.

REMOVAL & INSTALLATION

1. On most models, top of mixture control unit must be removed to extract mixture screw plug or steel ball which blocks access opening. Tap plug or ball out with pin punch.
2. Clean around all fuel line connections. Remove fuel lines and wipe up any spilled fuel. Disconnect electrical wiring and remove rubber boot to manifold. Remove Allen screws and lift off mixture control unit.
3. To install, reverse removal procedure. Replace gaskets and seals. Check for leaks after installation.

FUEL DISTRIBUTOR

1. Remove mixture control unit. Remove 3 screws from top of fuel distributor. Lift fuel distributor carefully to ensure that plunger does not fall out.
2. Only line pressure regulator shims may be replaced. If either control plunger or regulator piston is scored, replace fuel distributor. Be sure new "O" ring is in place when installing fuel distributor.

Disconnect electrical plug and vacuum lines (if equipped). Remove fuel lines and wipe up any spilled fuel. Remove bolts and regulator. To install, reverse removal procedure.

Remove and plug hoses. Disconnect electrical plug. Remove regulator and mounting bolts. Reverse removal procedure to install.

Remove electrical connector and fuel line. Loosen mounting bolts and remove cold start valve. Check "O" ring or gasket. Replace if necessary. Install valve.

1. Clean area around valves. Hold valve secure and remove fuel line fitting. Do not allow valve to turn.
2. Remove retaining plate if present, and pull valves out carefully. Do not remove insulator sleeve, if possible.
3. To install, reverse removal procedure. Replace "O" rings and lubricate with drop of oil. Place injectors in sleeve and press until seated. Tighten fuel lines and check for leaks.

THERMO TIME SWITCH

Drain coolant below level of switch. Be careful not to damage connectors on switch while removing. Coat threads of sensor with sealant and reinstall.

FREQUENCY VALVE

1. Disconnect electrical connector. Hold small nut at hose and loosen larger valve nut. DO NOT spill gasoline on rubber mounting insulator as it will cause rubber to swell.
2. Remove return lines at fuel distributor and/or control pressure regulator. To install, reverse removal procedure. Use new gaskets. Check for leaks after installation.

ECU

Remove weatherstrip from lower leading edge of right front door. Remove right side lower kick panel. Remove mounting screw on upper leading edge of ECU. Disconnect multi-pin connector and remove ECU. To install, reverse removal procedure.

1. Disconnect wiring from sensor. Remove shield from sensor if equipped. Remove sensor. Coat threads of new sensor with anti-seize compound. Take care not to get compound into slots on end of sensor.
2. Install sensor and tighten to 25-30 ft. lbs. (35-41 N.m) on all models. Refit shield and connect sensor wire.

See also:
• CIS (LAMBDA) FUEL PRESSURES