Programmed repairs: Carburetor system Engine 102 - 2 E-E Carburetor

Programmed Repairs Engine 102 2 E-E Carburetor Combustion IVa

07.2 Carburetor System

Possible causes

1. Starting and warming-up mixture or acceleration mixture too lean.

2. Intake manifold heater not operating.

3. Incorrect resistance trimming plugs for ignition and carburetor system.

Remedy

1. a) Check choke gap at +20 °C. If gap is not in order, test ground supply for control unit (N45) (Repair Instructions 07.2-0903-114).

b) If choke gap is in order, install larger idle fuel and main nozzle for 1st stage.

1) Replacement only necessary up to carburetor production date 7343.

2) Fitted as standard as of carburetor production date 8336.

2. a) Test electric intake manifold heater (Repair Instructions 07.2-0903-114).Install only heating grille with part no. 102 140 01 70 (Siemens). This heating grille is fitted as standard as of 10/89.
Recognizable from: material aluminium.
b) Test intake manifold warm water heater by briefly opening radiator pressure cap when engine is at normal operating temperature, releasing pressure and closing cap again (not applicable if engine is cold).

Detach coolant hose at intake manifold (below carburetor at water tank). Open radiator pressure cap. A strong jet of water should flow out of the hose connection fitting. If not, remove intake manifold, remove core plug from cylinder head.

3. Test resistance trimming plugs for ignition and carburetor system, replace if necessary (KAT vehicles).

Cause

Throttle valve actuator potentiometer signals incorrect value to 2 E-E carburetor control unit.

Remedy
Provided the throttle control operates smoothly, replace throttle valve actuator. Part no.

000 070 02 65, alternatively 000 070 00 65.

Possible causes

1. Second carburetor stage does not open (start of opening 1600-1800/min, fully open as of approx. 2500/min at full load).

2. Lack of fuel.

3. Speedometer lag, has no phase lead.

4. Lambda control does not switch off at full load with the result that mixture is too lean.

5. Air admitted to float chamber when driving.

Remedy

1. Check second carburetor stage for full opening:

a) on dynamometer (Repair Instructions 2 E-E Carburetor op. no. 07.2-110),

b) on road by driving at approx. 70 km/h in third gear, and suddenly depressing accelerator to full throttle; after 2-4 seconds econometer pointer should move to end stop of red panel.

If pointer does not move to end stop, second stage does not open; check smooth mechanical operation, if necessary.

Check vacuum hose and diaphragm unit for

leaks. Drill restrictor in vacuum hose (0.5 mm

dia.), open to approx. 0.8 mm dia. Take off

carburetor cover, drill open brass restrictor

0.7 mm dia. in vacuum passage (rectangular recess) to 0.8 mm dia. Check that vacuum bore in 1st and 2nd stage is clear.

Note
As of carburetor production date 7343 (stamped next to float chamber air admission valve) the 2nd stage control has been modified and restrictor is no longer fitted in vacuum hose.
It is then not necessary to widen the restrictors.

2 a) Feel fuel feed hoses to carburetor to determine whether a restrictor is installed; if so, remove restrictor.

b) Check delivery by detaching connector
for position sensor at EZL ignition control
unit so that engine does not start. Operate
starter for 20 seconds, measure delivery.
Specification: approx. 0.25 liters. If delivery
is insufficient, check suction and pressure
side of fuel pump (Repair Instructions 2 E-E
Carburetor, op. no. 07.2-130).

c) Install larger main nozzle (X112.5) in 1st stage, part no. 000 071 91 35.

3. Perform speedometer comparison at approx.
160 km/h on roller dynamometer.


Use shop test tyres. See also Group 54: "Vehicle does not reach top speed, speedometer has insufficient phase lead".

4. Check whether lambda control switch is off at full load by driving on dynamometer or on the road with lambda control tester connected; pointer must no longer fluctuate; check and adjust full throttle stop if necessary.

5. Check float chamber air admission (Repair Instructions 2 E-E carburetor,
op no. 07.2-114).

Cause
Choke is not pressed in opening direction by spring force because retaining ring below the compression spring for idle correction air needle control has jumped off.

Remedy

With engine stopped, push choke fully closed then release slowly; the choke must be pushed fully open by the spring force; replace carburetor if necessary.

Cause
Mixture too lean.

Remedy
Install larger idle and main nozzle (Repair

Instructions 2 E-E carburetor op. no. 07.2-160).

1) Replacement only necessary up to carburetor production date 7343.

2) Fitted as standard as of carburetor production date 8336.

Cause

Vibration noise of choke (100 Hz).

Remedy
None, as caused by operation.

1st cause
Engine ground cable (W11) for control unit (bolted onto cylinder at front left) has open circuit, poor contact.

Remedy
Check whether engine ground cable (W11) is tight and has continuity. At the same time, unscrew ground cable (W10) at right spring dome, check whether all cables are correctly soldered. Clean contact surfaces.

2nd cause

Electric lead from lambda sensor to contact 8 of control unit has short to ground.

Remedy
Test electric lead for short to ground by disconnecting coupling at control unit when engine is not running and measure resistance between contacts 7 and 8. Specification:  W.

If reading differs from specification, a short to ground exists; test oxygen sensor if necessary. If in order, a short to ground exists at cable between plug connection of oxygen sensor and control unit (e.g.: screening is contacting cable core).

3rd cause

Air admitted to float chamber when driving.

Remedy
Check float chamber air admission (Repair

Instructions 2 E-E carburetor, op. no. 07.2-114).

Possible causes

1. Float chamber air admission valve does not switch over to internal air admission (mixture too rich).

2. Malfunction of throttle valve actuator (e.g. evacuation valve no longer returns to closed position after opening, or valves leaking).

3. On vehicles up to end May 1986 the mixing pipe for idle system may not have been installed.

1st remedy
Check float chamber air admission (Repair

Instructions 2 E-E carburetor, op. no. 07.2-114).

2nd remedy
Check operation of air admission and evacuation valve of throttle valve actuator (Repair Instructions 2 E-E carburetor, op. no. 07.2-114).

Note
The valves of the throttle valve actuator have bee modified as of production date 6 224 (=August 1986, stamped on metal cover).

If the two tests of the valves do not reveal a clear fault, throttle valve actuators prior to production date 6 224 should be replaced on suspicion.

3rd remedy
Fit on new carburetor as a test (Repair Instructions 2 E-E carburetor, op. no. 07.2-156).

The cutting out of the engine may be caused by various factors. Usually this is a malfunction of the throttle valve actuator, the plunger is retracted too far. A malfunction of the choke, sudden closing or complete opening can also be the cause.

Possible causes

1. Air admission line for throttle valve actuator is sometimes blocked or is incorrectly fitted on.
For example: is connected to control line for fuel evaporation control system and is thus supplied with vacuum.

2. Hairline crack in distributor cap, cables to ignition coil loose (engine cuts out particularly under load).

3. Wiring harness for electric control of carburetor damaged at bracket on valve cap (cables briefly contacting, or briefly shorting to ground at bracket; move cables to locate fault).

4. Malfunction of throttle valve actuator or choke actuator.

5. No engine speed signal at all or occasionally. No voltage supplied to contact 13 of control unit or sporadic interruptions. Ground supply for throttle valve actuator potentiometer or throttle valve potentiometer constantly or briefly interrupted.

6. Metal closing plate for fuel shutoff for limiting maximum engine speed has detached from plastic piece (ball head jumped out) and is sucked against the nozzle assembly (fuel shutoff).

7. Air admitted from outside to float chamber when driving.

8. Ignition control unit has cold solder point or crankshaft position sensor sometimes does not operate.

Remedy

1. Detach air admission line at throttle valve actuator (top connection), test drive vehicle. If fault has been rectified, pull air admission line out of rubber grommet in fire wall, check for kinks and clear passage. Push line only approx. 80 mm through the rubber grommet.
Check that lines of fuel evaporation control system are correctly connected.

2. Replace distributor cap, secure wiring if necessary.

3. Detach wiring harness at bracket, cut open insulating sheathing, check whether wiring is damaged, insulate if necessary or insert new section of wiring.

4 To distinguish whether the cause exists at the throttle valve actuator or at the choke actuator, proceed as follows:

With engine idling, detach electrical connector for throttle valve actuator, test drive. Then detach electrical connector at choke, test drive.

If engine does not run (too lean), unscrew mixture regulating screw far enough until idle speed is in order.

If the fault no longer occurs when the connector is unplugged, a malfunction of the respective component exists; replace throttle valve actuator or choke actuator.

Note
The valves of the throttle valve actuator have been modified as of production date 6.224 (=August 1986, stamped on metal cover).
In cases of doubt, replace throttle valve actuators prior to production date 6.224.

5. Check wiring and plug connections for loose contact by moving wiring or plug connection with engine running; engine speed must not alter when performing this step.
Check electric cable routing according to wiring diagram, check plug connections for proper contact, test wiring for continuity and short circuit by unplugging all connectors. Unscrew ground cable (W10) at right spring dome, check whether all wiring is correctly soldered. Clean contact surfaces. Replace throttle valve potentiometer.

6. Apply full throttle by hand. As soon as engine speed has risen to 3000-4000/min, briefly press open choke as far as the stop and immediately release again, while continuing to hold full throttle. If the engine cuts out, the closing plate is loose (repeat
test several times). Remove carburetor
cover if necessary, remove screw plugs at
nozzle assembly. Turn plastic part through
180°, take out metal closing plate. Carefully
insert new metal closing plate, part no.
000 072 01 41 05, into plastic part.

Note
On no account detach actuating rod of fuel shutoff at the top. Fault may occur up to carburetor production date 7.033 (number is stamped on carburetor cover next to float chamber air admission valve).

7. Check float chamber air admission (Repair Instructions 2 E-E carburetor, op. no.
07.2-114).

8. Replace ignition control unit as a test, test crankshaft position sensors, replace if necessary.

1st cause
Carburetor overflowing.

Remedy
Illuminate mixing chambers and check whether fuel flows out at the pre-atomizer; clean float needle valve if necessary. Check float weight (7.90.5 g), install new float if necessary.
Check float level.

2nd cause
Idle fuel nozzle loose.

Remedy
Screw in mixture regulating screw fully. If the pointer of the lambda control tester remains against stop and the CO level does not drop below 0.5%, remove carburetor cover, check whether idle fuel nozzle is tight.

Before CO test, run engine for approx. 1 min at 3000 min.

Cause
Incorrect resistance trimming plug (ECE version)

for 2 E-E carburetor control unit installed, for this reason lambda control is not activated.

Remedy
Install KAT version of resistance trimming plug, part no. 014 545 71 28.

Cause
Occasionally fluctuating ignition timing value (e.g. up to 15° CA after TDC or up to more than 30° before TDC when idling). Irregular voltage pattern at flywheel position sensor affects ignition control unit in such a way that illogical ignition timing values are transmitted. Fault has occurred so far only on vehicles with automatic transmission and Bosch ignition control unit.

Remedy
As a test, install Siemens ignition control unit,

part no. 006 545 41 32, and position sensor.

If this does not rectify fault, replace flywheel as segment faults may exist.

Cause

Idle air nozzle worn, idle mixture can therefore not be set by adjusting mixture regulating screw.

Remedy
Check whether idle air nozzles are worn by:

1. pushing choke closed by hand (enriching) far enough for engine still to run smoothly. Pointer of lambda control tester should now move away from right-hand stop.

2. Run engine at approx. 2500/min. Pointer of lamda control tester should not fluctuate.

If both conditions are met, the idle air nozzle is worn and must be replaced (Repair Instructions 07.2-159).