0114 - Testing routine: Engine 102 - 2 E-E Carburetor A. Component arrangement, B. Test equipment, C. Test connection diagram, D. Contact assignment, E. Conditions/test instr. F.-K. Readouts/wiring diagrams

Multimeter

e. g. Sun, DMM-5
Thorn EMI
Avometer 2003

Engine tester

e. g. Bosch, MOT 002.02

Lambda control tester

e. g. Hermann, L 115

Engine revolution counter

On/off ratio readout (constant)

Possible cause of fault

Test table:

Test step

10%

Interrupt/short-circuit, control unit (N45)  throttle valve potentiometer (R24). Interrupt/short-circuit throttle valve potentiometer (R24).

1

3

20%

Interrupt/short-circuit control unit (N45)  throttle valve actuator (Y22/2). Interrupt/short-circuit potentiometer of throttle valve actuator (Y22/2). Malfunction of throttle valve actuator (leak, valve jamming).

1

5

30%

No coolant temperature signal. Interrupt/short-circuit control unit (N45) coolant temperature sensor (B11/2).

No engine ground (W11) at control unit.

1

2

50%

a) Cars without lambda control: no fault in area of monitored signals.

-

b) Cars with lambda control: oxygen sensor not operational (too cold) or faulty. Interrupt oxygen sensor  control unit (N45).

1

8

70%

No TD signal (engine speed). Interrupt/short-circuit ignition control unit (N1/2)  control unit (N45).

1

6

80%

a) Ground control line for relay (K3) of intake manifold heater  control unit (N45) contact 14 has connection to battery positive (short-circuit).

b) Throttle valve actuator:

Short-circuit in cables for evacuation or air admission valve

 control unit (N45). Short-circuit of solenoid coils of valves.

c) Cable of control unit (N45) contact 15  ignition control unit (N1/2)

Pin 4 connection to battery positive.

1

5

12

14

90%

Interruption/short-circuit resistance trimming plug (R19)  control unit (N45). No resistance trimming plug.

1

11

Position

Function

Complaint

1

Basic setting

-

2

Lean mixture over entire performance map.

High fuel consumption.

3

Enriching, dynamic and static performance map, at engine speeds < 2000 rpm and coolant temperature < 18 °C.

Transition fault, jerking at engine speeds
< 2000 rpm and coolant temperature

< 18 °C.

4

Enriching, dynamic and static performance map, over entire engine speed range and coolant temperature < 18 °C.

Transition fault, jerking over entire engine speed range at coolant temeprature
< 18 °C.

5

Enriching dynamic performance map

< 2000 rpm over entire coolant temperature range.

Enriching static performance map at engine speed < 2000 rpm and coolant temperature up to 60 °C (only if engine started at coolant temperature < 18 °C).

Transition fault, at engine speed

< 2000 rpm over entire coolant temperature range.

Jerking at engine speed < 2000 rpm and coolant temperature up to 60 °C (only if engine started at coolant temperature
< 18 °C).

6

Enriching over entire dynamic performance map.

Enriching over entire stationary performance map up to 60 °C coolant temperature (only if engine started at coolant temperature < 18 °C).

Transition fault over entire coolant temperature range.

Jerking up to 60 °C coolant temperature (only if engine started at coolant temperature

< 18 °C).

7

Idle speed increase by 100 rpm.

-

Resistance trimming plug position

Resistance (W)

Voltage (V) 0.1

1

953

2.81

2

1 270

3.16

3

1 620

3,43

4

2 260

3.77

5

3 320

4,10

6

5 360

4.40

7

11 500

4.72

Position

Function

Complaint

1

Basic setting

2

Lean mixture over entire performance map

High fuel consumption

3

Enriching at engine speed < 2000 rpm and coolant temperature < 18 °C.

Transition fault, jerking at engine speed
< 2000 rpm and coolant temperature

< 18 °C.

4

Enriching over entire engine speed range and coolant temperature < 18 °C.

Transition fault, jerking over entire engine speed range at coolant temperature
< 18 °C.

5

Enriching at engine speed < 2000 rpm over entire coolant temperature range.

Transition fault, jerking at engine speed
< 2000 rpm over entire coolant temperature range.

6

Enriching over entire dynamic and static performance map (at all engine speeds over entire coolant temperature range).

Transition fault, jerking over entire coolant temperature and engine speed range.

7

Idle speed increase by 100 rpm.

-

Resistance trimming plug position

Resistance (W)

Voltage (V) 0.1

1

51

0.33

2

105

0.61

3

169

0.92

4

249

1.26

5

348

1.61

6

442

1.88

7

590

2.22

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

1

Voltage and ground supply of control unit (N45)

Ground supply

a) Battery ground (W10)

N45

 

20  +

Ignition: OFF control unit (N45) disconnected.

11-14 V

Battery ground (W10) loose, interrupt, contact fault.

b) Engine ground (W11)

N45

 

2  +

Ignition: OFF control unit (N45) disconnected.

11-14 V

Engine ground (W11) loose, interrupt, contact fault.

c) Ground for:

 Throttle valve potentiometer (R24)

 Throttle valve potentiometer (Y22/2)

 Resistance trimming plug (R19)

 Screening O2 sensor cable

N45

 

7  +

Control unit (N45) connected.

11-14 V

Control unit (N45)
faulty.

d) Test ground under load

N45



2  20

Detach coolant

temperature

sensor

connector

(B11/2),

connect with

2.5 kW test

resistor and

connect to

ground

(simulate
+20 °C).

Range mV

Ignition: ON

< 0,05 V

Battery ground (W10)

or engine ground

(W11) loose,

interrupt,
contact fault.

Control unit (N45)
faulty.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

Voltage supply

a) Continuous positive
(terminal 30a)

N45



2  1

11-14 V

Overvoltage protection fuse (K1/1) faulty, overvoltage protection relay (K1/1) missing, faulty or contact fault, interrupt: Battery (G1)  battery terminal block (X35)  overvoltage protection relay (K1/1), contact 1.

(See wiring diagram for contact assignment up to 08/86 ).

b) Ignition
(terminal 15)

N45



2  13

Ignition: ON

11-14 V

Overvoltage protection relay (K1/1) faulty, contact fault.

Interrupt: Ignition
starter switch (S2/1) fuse box (F1) interior engine plug connection (X26) overvoltage protection relay (K1/1) contact 3.
Interrupt: Overvoltage protection relay (K1/1) contact 6  control unit (N45) contact 13.

Note

Up to 08/86 terminal 15 for control unit (N45) was protected through fuse in fuse box (F1). Model 124 No. 11, Model 201, No. 2. (See wiring diagram for contact assignment.)

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

2

Coolant temperature sensor (B11/2)

N45



2  21

Control unit (N45) connected. Ignition: ON, engine at operating temperature (approx. 85 °C coolant temperature).

0.45-0.55 V

Interrupt/short-circuit control unit (N45) contact 21  temperature sensor (B11/2).

Control unit (N45)
faulty.

Resistance

N45



2  21

Ignition: ON, control unit (N45) disconnected.

Engine at operating (approx. 85 °C coolant temperature).

230-300 W

If wiring in order, test resistance; renew coolant temperature sensor (B11/2), if necessary.

Coolant temperature °C

Resistance (W)

Voltage (V)

- 20

- 10

 0

+ 10

+ 20

+ 30

+ 40

+ 50

+ 60

+ 70

+ 80

+ 90

15 670

9 450

5 890

3 790

2 500

1 692

1 170

826

594

434

322

243

4.1 - 4.5

3.7 - 4.1

3.3 - 3.7

2.8 - 3.3

2.3 - 2.8

1.8 - 2.3

1.4 - 1.8

1.1 - 1.4

0.8 - 1.1

0.7 - 0.8

0.5 - 0.6

0.4 - 0.5

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

3

Throttle valve potentiometer (R24)

a) Voltage supply

N45



7  18

Control unit (N45) connected. Ignition: ON

4.6-5.1 V

Interrupt/short-circuit (N45) contact 18  throttle valve potentiometer (R24)
pin 2.

Interrupt control unit (N45) contact 7  throttle valve potentiometer (R24)
pin 3.

Control unit (N45)
faulty.

b) Potentiometer range

N45



7  11

Ignition: OFF,

after 10

seconds

ignition: ON

(plunger of

throttle valve

actuator fully extended).

Slowly apply full throttle.

1.0-1.5 V

Voltage should rise up to
> 4.2 V

Interrupt/short-circuit (N45) contact 11 throttle valve potentiometer (R24)
pin 1.

Interrupt control unit (N45) contact 7  throttle valve potentiometer (R24)
pin 3. Connector of throttle valve potentiometer missing.

c) Potentiometer resistance:

 Total resistance

N45



7  18

Ignition: OFF, control unit (N45) and throttle valve actuator connector detached. (Throttle valve actuator plunger fully extended).

1.4-2.6 kW

If wiring in order, test resistances of throttle valve potentiometer, replace throttle valve potentiometer if necessary.

 Wiper contact resistance in adjustment range

N45



7  11

As above, then apply full throttle.

> 500 W

1.4-2.6 kW

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

4

Choke actuator (Y22/1)

N45



12  10

Control unit (N45) and throttle valve actuator connector attached. Choke moves easily.

Ignition: ON, engine at operating temperature.

0.2-0.5 V

Interrupt/short-circuit

control unit (N45)

contact 10  choke

actuator connector

(contact 1).

Interrupt control unit (N45) contact 12  choke actuator connector (contact 2). Test coolant temperature sensor (B11/2) (test step 2).

N45



12  10

Ignition: OFF install 2.5kW test resistor. After 10 seconds ignition: ON,
do not take voltage reading until stable.

1.8-2.2 V with maximum choke gap 1.5 mm (measured at top vane).

If wiring and coolant temperature sensor are in order and variation from specification exists, test coil resistance of choke actuator (Y22/1).

Coil resistance

N45



12  10

Ignition: OFF control unit (N45) disconnected.

1.2-1.8 W

Renew choke actuator (Y22/1).

5

Throttle valve actuator (Y22/2)

Switching noise from evacuating valve

N45



1  9

Ignition: OFF control unit (N45) disconnected.

Valve switching noise must be audible each time connection is made.

Interrupt/short-circuit control unit (N45) contact 9 or 3  throttle valve actuator (Y22/2) contact 3 or 8.

Switching noise from air admission valve

N45



1  3

Interrupt and re-establish connection several times.

If wiring in order, test coil resistance.

Coil resistance of evacuation valve

N45



2  9

Ignition: OFF, control unit (N45) disconnected.

25-40 W

Replace throttle valve actuator (Y22/2).

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

Coil resistance of air admission valve

N45



2  3

Ignition: OFF, control unit (N45) disconnected.

25-40 W

Renew throttle valve actuator (Y22/2).

Control of evacuation valve

N45



2  9

Control unit (N45) connected. Engine idling, then switch off.

When switching off for approx.
3 seconds 11-14 V (plunger retracted).

Control unit (N45)
faulty.

Control of air admission valve

N45



2  3

Engine idling, then switch off.

When switching off after approx. 3 seconds for approx.
3 seconds 11-14 V (plunger moves out).

Control unit (N45)
faulty.

Throttle valve actuator potentiometer

a) Voltage supply

N45



7  18

Control unit (N45) connected. Ignition: ON

4.6-5.1 V

Interrupt/short circuit control unit (N45) contact 18  throttle valve actuator potentiometer contact 5.

Interrupt control unit (N45) contact 7  throttle valve actuator potentiometer contact 4.

Control unit (N45)
faulty.

b) Potentiometer range

N45



7  17

Control unit (N45) connected. Engine idling, then switch off.

approx.
3 seconds 0.2-0.5 V then approx. 3 seconds >3.5 V then 0 V.

No passage in air admission line for throttle valve actuator. Interrupt/short-circuit control unit (N45) contact 17  throttle valve actuator contact 7or control unit (N45) contact 7  throttle valve actuator contact 4.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

Potentiometer resistances:

 Total resistance

N45



7  18

Ignition: OFF Control unit (N45) and throttle valve potentiometer connector detached.

1.4-2.6 kW

If wiring in order, replace throttle valve actuator (Y22/2).

 Wiper contact resistance in adjusting range

N45



7  17

As before (throttle valve actuator plunger fully extended).

1.2-2.4 kW

Throttle valve actuator (Y22/2) leaking (valves, diaphragm), renew if necessary.

Leaktightness of evacuation valve

N45



7  17

Control unit (N45) disconnected.

Throttle valve potentiometer connector attached, start engine. (Fast running)

Reading from previous test must drop maximum 200 W within one minute.

Leaktightness of air admission valve

N45



1  9

Control unit (N45) disconnected. Run engine until throttle valve actuator plunger is retracted, separate electrical connection contacts 19.

< 400 W

Reading must rise maximum 200 W within one minute.

N45



7  17

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

Ease of movement of plunger of throttle valve actuator

Control unit (N45) connected. Run engine. Switch off engine and at the same time check plunger of throttle valve actuator.

Actuator must retract fully for approx.
3 seconds then move out fully within
2 seconds.

Insufficient or no passage in air admission line for throttle valve actuator (Y22/2).

Throttle valve actuator (Y22/2) faulty.

6

TD signal
(engine speed)

N45



2  25

Control unit (N45) connected. Engine idling, then increase engine speed.

12-2 V (dropping as engine speed rises).

Interrupt/short-circuit of ignition control unit (N1/2)  diagnostic socket terminal block terminal TD .

a) manual transmission

Compressor cutout control unit (N6) (only if A/C fitted)  Control unit (N45) contact 25.

b) automatic transmission

Kickdown cutout relay (N15)  compressor cutout control unit (N6) (only if A/C fitted)  control unit (N45) contact 25.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

7

Idle signal for EZL ignition control unit (N1/2)

N45



2  6

Control unit (N45) connected, engine idling.

<0.6 V

Basic setting of throttle valve actuator incorrect.

Partial throttle approx.
2000 rpm.

10-14 V

Check throttle valve potentiometer and potentiometer of throttle valve actuator.

Interrupt/short-circuit (N45) contact 6  ignition control unit (N1/2).

8

O2 sensor

N45



7  8

Control unit (N45) connected. Engine and O2 sensor at operating temperature.

a) Sensor signal

Press choke open far enough for engine to still run (leaner mixture).

approx.
0.1 V

O2 sensor (G3/2) not operational (too cold), O2 sensor heater faulty.

Engine idling; press choke closed far enough for engine to still run (richer mixture).

approx.
0.9 V

Interrupt/short-circuit
O2 sensor (G3/2)  plug connection O2 sensor signal  control unit (N45) contact 8.

If smaller specified level is not reached, check whether idle mixture is not set too rich or if carburetor slightly flooded (e. g.: drips from pre-atomizer).

If wiring in order and specified valvues not reached, renew O2 sensor (G3/2).

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

b) O2 sensor heater

G3/2x1



between positive cable

Ignition: ON

Do not take reading until stable.

0.8-1.3 A

Overvoltage protection relay (K1/1) faulty, contact fault.

Interrupt/short-circuit (K1/1) contact 6 
O2 sensor connector (G3/2x1) contact 2.

O2 sensor faulty.

Note

Up to 08/86 O2 sensor heater was protected by fuse in fuse box.

Model 124 no. 11,

Model 201 no. 2.

9

Drive position cut-in signal

(automatic transmission)

N45



2  16

Control unit

(N45)

connected.

Ignition: ON,

selector lever

position P and

N.

all drive positions

0 V

5.0 V as from control unit part no. 006 545 51 32

11-12 V

Interrupt/short-circuit starter (M1) 

W124

Plug connection, starter wiring harness (X27)  starter lockout switch (16/1)  ignition starting switch (S2/1)  engine plug connection (X26)  control unit (N45) contact 16.

W201

Plug connection term. 50  electrical centre (F1)  starter lockout switch (S16/1)  ignition starting switch (S2/1)  plug connection, engine wiring harness (X26/3)  control unit (N45) contact 16.

Ground supply contact 16 control unit (N45) (manual transmission)

N45



16  1

-

11-14 V

Interrupt in ground cable.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

10

Air conditioner compressor cut-in signal

N45



2  19

Engine idling. Electromagn. clutch for air conditioning compressor engaged.

11-14 V

Interrupt/short-circuit control unit compressor cutout (N6) (terminal 87z)  control unit (N45) contact 19.

11

Resistance trimming plug (R19)

N45



7  22

Ignition: OFF.

Control unit

(N45)

disconnected.

Plug position

"1"

KAT

ECE

953 W

51 W

No resistance trimming plug (R19).

Interrup/ short circuit in resistance trimming plug  control unit (N45) contact 7 or 22.

12

Intake manifold and bypass heater

a) Relay control (K3)

N45



2  R8

Control unit (N45) connected.

2.5 kW test resistor installed.

11-14 V

Interrupt/short-circuit overvoltage protection (K1/1) contact 6  intake manifold heater relay (K3) contact 4.

N45



 

2 R8/1

Run engine. (Remove test resistor after testing).

11-14 V

Relay (K3) contact 1  carburetor heater (R8/1) or intake manifold heater (R8).

Connection to control unit positive (N45)

contact 14  relay (K3) contact 5.

Relay (K3) or control unit (N45) faulty.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

Current consumption of intake manifold heater

K3 K3

 1   3

Engine at operating temperature, control unit (N45) connected. Carburetor heater connector (R8/1) detached. Engine idling.

Do not take reading of amperage until stable.

7-13 A

Intake manifold heater (R8) faulty, renew if necessary.

Current consumption of carburetor heater (R8/1)

K3 K3

 1   3

As before, but carburetor heater connector (R8/1) plugged in and intake manifold heater connector (R8) detached.

1.5-3.0 A

Carburetor heater (R8/1) faulty; renew if necessary.

13

Float chamber vent valve (Y18)

N45



2  

Y18

Control unit (N45) connected.

Detach hose for float chamber vent at charcoal canister, suck at hose.

11-14 V

Ignition: ON

Ignition: OFF

No

continuity

Continuity

Interrupt/short-circuit overvoltage protection (K1/1) socket 6  intake manifold heater relay (K3) contact 4  float chamber vent valve connector (Y18).

Float chamber vent valve (Y18) faulty.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

14

Throttle valve actuator fault signal for ignition control unit EZL (N1/2)

N45



2  15

Ignition: OFF
Simulate throttle valve actuator fault by detaching vacuum hose at evacuation valve of throttle valve actuator (Y22/2) (bottom hose).

Run engine at idling speed.

>3 V (dependent on ignition control unit version

4.6-5.1 V
or
11-14 V.)

Firing point up to 12° after TDC.

Short-circuit control unit (N45) contact 15  ignition control unit EZL (N1/2)

Connector 4.

Ignition control unit or control unit (N45) faulty.

N45



2  15

Re-connect detached vacuum hose.

<0.7 V and firing point 11-15° BTDC.

Short-circuit control unit (N45) contact 15  ignition control unit EZL (N1/2). Connection to battery positive. Ignition control unit or control unit (N45) faulty.

15

Intake air preheater

Detach warm air hose at air filter.

Check position of warm air flap (visual inspection).

below approx.
+20 °C.

above approx.

+30 °C.

(ambient temperature)

Air flap

closed.

Air flap

open.

Thermo control element for warm air flap faulty.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

16

Leaktightness of intake system

Connect engine revolution counter and CO tester.

Engine idling
at normal operating temperature.

Spray all sealing points with ISO-Octane DIN 51 756 or cleaning naphtha.

KAT

Pointer of lambda control tester should not move to the left. Engine speed should not vary.

RÜF

Engine speed and CO reading should not vary.

Seal intake system.

17

2nd carburetor stage (full opening)

Connect engine speed tester.

Apply full throttle. As soon as engine speed has risen to 4000 to 5000 rpm, hold both carburetor mixing chambers closed with your hands far enough for the engine to run at approx.
2500 rpm.

Keep a check on actuating rod of 2nd stage vacuum cell.

Actuating rod should be retracted as far as the stop.

Check vacuum supply for 2nd stage vacuum cell and leaktightness (07.2-169).

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

18

Full throttle stop

Ignition: OFF. Depress accelerator pedal of manual transmission fully, of automatic transmission as far as the stop on the kickdown switch.

Check throttle valve lever and full throttle stop at carburetor.

Throttle valve lever must be resting against full throttle stop.

Adjust full throttle stop (07.2-110).

19

Carburetor nozzles

Remove carburetor cover, check that nozzle passage is clear and of correct size (visual inspection).

Passage clear and nozzle of specified size.

Blow fuel nozzles and passages clear with compressed air; replace fuel nozzles if necessary.

20

Fuel pump

Connect vacuum pressure gauge.

Suction side: Operate starter until vacuum no longer rises.

330-600 mbar. Maximum permissible pressure drop in first minute
95 mbar.

Pressure side: Operate starter until pressure no longer rises.

0.20-0.40 bar (gauge pressure), maximum permissible pressure drop in first minute
0.05 bar.

Fuel pump faulty.

Test step/
Test scope

Tester/
Test connection

Operation/
Requirement

Specification

Possible cause/
Remedy

21

Setting 2 E-E resistance trimming plug (R19) to correct position

Visual inspection of setting of resistance trimming plug.

Basic setting KAT and RÜF position "1".

If necessary, re-set resistance trimming plug depending on complaint (07.2-114, Section H).

22

Carburetor flooding

Run engine until hot.
Fuel tank overpressure should have been built up.

Visual inspection of pre-atomizer of 1st and 2nd stage.

No fuel should flow out.

Check valve in fuel return line leaking or incorrectly installed.

Passage of float chamber vent hose not clear. Hose should be at a downward slope.

Float needle valve leaking, wrong float level.

Float too heavy because leaking (flooded with fuel).