Maintenance every 18,000 km (Mercedes-Benz E-Class W124)

Replacing spark plugs

Correct functioning of spark plugs is one of the most important conditions for efficient engine operation. It is necessary that only the prescribed type of spark plugs are installed on the engine. If the engine is in good condition, cleaning the spark plugs is a rare operation.

Removal the front cover on a DOHC engine with KE-JETRONIC injection system

Unscrewing the screws securing the spark plug cover

Removal the spark plug cover

Removal the spark plug wire on a 6-cylinder DOHC engine

Removal the high-voltage wire from the spark plug on a 4-cylinder engine

Removal the spark plug from a 6-cylinder DOHC engine

Removal a spark plug from a 4-cylinder engine

Removal a spark plug from a 4-cylinder engine

Measuring spark plug gap using feeler gauge blade

Using a special tool to bend the side electrode of a spark plug

Screwing the spark plug into the engine

1. On DOHC engines with KE-JETRONIC injection system, remove the front cover, unscrew the screws and remove the cover covering the spark plugs (see fig. Removing the front cover on a DOHC engine with the KE-JETRONIC injection system, Unscrewing the screws securing the spark plug cover, Removing the spark plug cover).



2. On DOHC engines with HFM engine management, remove the ignition coils from the upper cylinder head cover.

3. Remove the spark plug wires from the spark plugs by pulling on the spark plug cap (see fig. Removing the high-voltage wire from the spark plugs on a 6-cylinder DOHC engine, Removing the high-voltage wire from the spark plug on a 4-cylinder engine).

4. Clean the spark plugs using a brush, vacuum cleaner or compressed air to prevent dirt from getting into the engine cylinders after removing the spark plugs.

5. Using a spark plug wrench, remove the spark plugs (see fig. Removing the spark plug from a 6-cylinder DOHC engine, Removing the spark plug from a 4-cylinder engine, Removing the spark plug from a 4-cylinder engine).

6. Visual inspection of the working part of the spark plugs can show the condition of the engine. If the nose of the spark plug insulator is clean and white, without any deposits, this indicates that the mixture is too lean. This also indicates that the plug is too hot, i.e. the heat from the central electrode is slowly removed. If this is the case, it is necessary to adjust the mixture or replace the plug.

7. If the nose of the spark plug insulator is covered with a black coating, this indicates that the mixture is too rich. If the coating is black and oily, this indicates engine wear and the need for inspection and repair. If the nose of the insulator is covered with a light brown coating, the mixture composition is optimal and the engine is in good condition.



8. The spark plug gap is very important because if the gap is too large or too small, the spark size changes, which leads to a decrease in engine efficiency. The gap must always meet technical requirements.

9. The gap is checked with a wire template or feeler gauge. The gap is adjusted by bending the side electrode. The central electrode should never be bent, as this can cause the insulator to break and the spark plug to fail (see fig. Measuring spark plug gap using feeler gauge blade).

10. To bend the side electrode of the spark plug, you need to use a special tool (see fig. Using a special tool to bend the side electrode of a spark plug).

11. Before installing the spark plug into the engine, check that the threads are clean and all threads are intact.

12. To screw the spark plug several turns, you can use a piece of rubber hose, insert the spark plug insulator into one end and, rotating the hose, screw the spark plug several turns. Then you need to remove the hose and screw the spark plug to the required torque (see Fig. Screwing the spark plug into the engine).

13. Connect the high-voltage wires to the spark plugs and install all previously removed components.

Checking the components of the self-leveling rear suspension system

Removal the dipstick from the reservoir of the self-leveling rear suspension system

Rear self-leveling suspension fluid level

The fluid level in the self-leveling rear suspension system should be between the MIN and MAX marks on the dipstick.



Below is the procedure for performing work on models with a station wagon body.

1. Place the vehicle on a level surface and open the hood. Check the fluid level in the rear self-leveling suspension system on an unladen vehicle.

2. Remove the dipstick and wipe the fluid off the dipstick with a clean rag. Insert the clean dipstick into the reservoir and remove it again. Check the fluid level, which should be between the MAX and MIN marks on the dipstick (see fig. Removing the dipstick from the reservoir of the self-leveling rear suspension system, Fluid level in the self-leveling rear suspension system). If the fluid level is checked in a loaded vehicle, the fluid level may be below the MIN mark.

3. If necessary, add the required amount of the specified fluid through the dipstick hole.

Checking the oil level in an automatic transmission

Check the oil level in the automatic transmission with the transmission warmed up (oil temperature 80°C).

Removal the Automatic Transmission Oil Dipstick

Using a rag to clean the automatic transmission oil dipstick

Location of marks on the dipstick for measuring the oil level in an automatic transmission

1. Place the vehicle on a level, horizontal surface.



2. Start the engine at idle speed and move the selector lever to position P and apply the handbrake.

3. Release the locking lever, remove the transmission oil dipstick, wipe it clean and reinstall it (see fig. Removing the automatic transmission oil dipstick, Using a rag to clean the automatic transmission oil dipstick).

4. Remove the oil dipstick and check that the oil level is between the MIN and MAX marks (see Fig. Location of marks on the dipstick for measuring the oil level in an automatic transmission).

5. If the oil level is below the MIN mark, add oil through the dipstick hole.

6. If there is a need to frequently top up the oil, then there is a leak that needs to be found and fixed before it leads to serious consequences.

Checking the tightness of the hoses and fluid leakage

Cooling system leaks are usually detected by a white or rust-colored coating in the area adjacent to the leak.

1. Carefully inspect the radiator and coolant hoses along their entire length. Replace any hoses that are cracked, torn, or showing signs of wear. Cracks are easier to spot if the hose is pinched. Pay particular attention to the clamps that attach the hoses to the cooling system components. Hose clamps that have been tightened too much can cause the hose to rupture or puncture, resulting in leaks in the cooling system. Inspect all hoses and hose connection surfaces for leaks. If any leaking problems of this nature are found, replace that component or gasket.

2. Fuel leaks are difficult to pinpoint until the leak is significant and therefore easily visible. Fuel tends to evaporate quickly once it comes into contact with air, especially in a hot engine bay. Small droplets may disappear before you can pinpoint the leak. If you suspect a fuel leak in the engine bay area, then cool the engine and run it while it is cold with the hood open. Metal objects tend to shrink when cold and rubber hoses tend to loosen, so any leaks will be more obvious as the engine warms up from cold starting.



3. If there are signs that there is a leak of some kind of fluid, but you cannot identify the type of fluid or the exact source, then you should leave the car for a long time and put a large piece of paper or rag under the car. This will help to find the place of the leak and also help to identify the leaking fluid by color. But keep in mind that some leaks may only appear when the engine is running.

4. A leak in the vacuum hose means that air is being sucked into the hose (but it doesn't come out of the hose), and this makes the leak very difficult to detect. The detection method is to use an old vacuum hose as a kind of stethoscope. Hold one end of the hose close to your ear (but not in the ear), and use the other end to probe the area around the suspected leak. When the end of the hose is directly over the leak, a hissing sound will be clearly audible through the hose. Avoid contact with hot or moving parts, as the engine must be running when checking.

Checking and replacing the auxiliary drive belt

1. With the engine off, inspect the entire length of the accessory drive belt. Check the accessory belt pulleys for nicks, cracks, deformation, and corrosion.

Replacing the auxiliary drive belt on a four-cylinder engine

Location of auxiliary drive belt tensioner mounting bolt (1) and adjuster nut (2) on 4-cylinder engines

Location of auxiliary drive belt on 4-cylinder engine without power steering

Location of auxiliary drive belt on 4-cylinder engine with power steering but without air conditioning

Auxiliary Drive Belt Location on 4 Cylinder Engine with Power Steering and Air Conditioning

1. Remove the radiator fan impeller and shroud.

2. Loosen the auxiliary drive belt tensioner mounting bolt by a quarter turn (see Fig. Location of auxiliary drive belt tensioner mounting bolt (1) and adjuster nut (2) on 4-cylinder engines).



3. Loosen the adjuster nut by turning it counterclockwise and unscrew the adjuster until the accessory drive belt is completely loosened. Remove the accessory drive belt from the pulleys.

4. Install the new drive belt onto the pulleys, starting with the tensioner pulley and continuing in the sequence shown in the illustrations Auxiliary Drive Belt Location on a 4-Cylinder Engine Without Power Steering, Auxiliary Drive Belt Location on a 4-Cylinder Engine with Power Steering but Without Air Conditioning, Auxiliary Drive Belt Location on a 4-Cylinder Engine with Power Steering and Air Conditioning.

5. Adjust the tension of the auxiliary drive belt as follows.

Models with a scale ruler on the tensioning mechanism

Adjusting the Auxiliary Belt Tension on 4-Cylinder Engines

To adjust the tension of the auxiliary belt on 4-cylinder engines, turn the adjuster nut (1) until the pointer (2) aligns with the fifth mark on the scale ruler (3).

1. On vehicles without power steering, turn the adjuster nut clockwise until the tensioner pointer aligns with the fifth mark from the left on the scale (see Fig. Adjusting the Auxiliary Belt Tension on 4-Cylinder Engines).

2. On models with power steering, turn the adjuster nut clockwise until the tensioner pointer is between the 8th and 9th marks from the left on the scale.

3. Tighten the tensioner mounting bolt to the specified torque.

4. Install the fan impeller and shroud.

Models with a single thick mark

Adjusting the tension of the auxiliary belt on a 4-cylinder engine

To adjust the tension of the auxiliary drive belt on a 4-cylinder engine, turn the adjuster nut (1) until the pointer (2) aligns with the thick line (3).

1. Turn the adjuster nut clockwise to align the tensioner pointer with the thick mark (see Fig. Adjusting the Auxiliary Belt Tension on a 4-Cylinder Engine).

2. Tighten the tensioner mounting bolt to the specified torque.

3. Install the fan impeller and shroud.

Replacing the Accessory Belt on 6-Cylinder SOHC Engines

Location of tensioner mounting bolt (1) and adjuster nut (2) on 6-cylinder SOHC engines

Auxiliary Drive Belt Location on 6-Cylinder SOHC Engine Without Air Fuel Pump

Auxiliary Drive Belt Location on 6-Cylinder SOHC Air-Fuel Pump Engines

1. Remove the radiator fan impeller and shroud.

2. Loosen the tensioner mounting bolt by 1/2 turn (see Fig. Location of the tensioner mounting bolt (1) and adjuster nut (2) on 6-cylinder SOHC engines).

3. Turn the adjuster nut counterclockwise to unscrew the adjuster to release the accessory drive belt. Remove the accessory drive belt from the pulleys.

4. Install the new accessory drive belt onto the pulleys, starting with the idler pulley and continuing in the sequence shown in the illustrations Accessory Drive Belt Location on 6-Cylinder SOHC Engines Without Air Fuel Pump, Accessory Drive Belt Location on 6-Cylinder SOHC Engines With Air Fuel Pump.

5. Adjust the tension of the auxiliary drive belt as follows.

Models with a scale ruler on the regulator

6-cylinder SOHC engine auxiliary drive belt tension adjusters

1. Move the tensioner pointer until it aligns with the right end of the scale when viewed from the front of the engine compartment (see Fig. Auxiliary Drive Belt Tension Adjusters for 6-Cylinder SOHC Engine).

2. On models without air conditioning, turn the adjuster nut clockwise until the tensioner pointer aligns with the fifth mark on the scale.

3. On models with air conditioning, turn the adjuster nut clockwise until the tensioner pointer aligns with the seventh mark on the scale.

4. Tighten the tensioner mounting bolt to the specified torque.

5. Install the fan impeller and shroud.

Models with a single thick mark in the tensioning mechanism

Auxiliary Drive Belt Tension Adjuster on 6-Cylinder SOHC Engine

1. Move the tension mechanism pointer so that the tip of the pointer aligns with the right narrowest end of the triangle.

2. Turn the adjuster nut clockwise until the tip of the tension indicator is aligned with the thick line (see fig. Auxiliary drive belt tension adjustment mechanism on 6-cylinder SOHC engine).

3. Tighten the tensioner mounting bolt to the specified torque.

4. Install the radiator fan impeller and shroud.

Replacing the Accessory Belt on 6-Cylinder DOHC Engines

Models with tension regulator indicator

Location of the plastic casing

The arrow indicates the one that needs to be removed to access the tensioner mounting bolt for the 6-cylinder DOHC engine with tension adjuster indicator.

Loosening the drive belt tensioner mounting bolt on a 6-cylinder DOHC engine with a tension adjuster indicator

Removal the auxiliary drive belt adjuster nut on a 6-cylinder DOHC engine

Accessory Drive Belt Location on a 6-Cylinder DOHC Engine

1. Remove the radiator fan impeller and shroud.

2. Loosen the tensioner mounting bolt by a quarter turn (see fig. Location of plastic cover, Loosening the drive belt tensioner mounting bolt on a 6-cylinder DOHC engine with a tension adjuster indicator).

3. Loosen the adjuster nut counterclockwise and back off the adjuster until the belt is completely loose. Remove the belt from the pulleys (see Fig. Unscrewing the auxiliary drive belt adjuster nut on a 6-cylinder DOHC engine).

4. Install the new accessory drive belt onto the pulleys, starting with the idler pulley and in the sequence shown in the illustration Accessory Drive Belt Location on a 6-Cylinder DOHC Engine.

5. Adjust the tension of the auxiliary drive belt as follows.

6. Move the tension mechanism pointer until the tip of the pointer aligns with the right narrowest end of the triangle on the scale ruler.

7. Turn the adjuster nut clockwise until the tip of the tensioner pointer aligns with the thick line on the scale (see fig. Auxiliary drive belt tension adjustment mechanism on 6-cylinder SOHC engine).

8. Tighten the tensioner mounting bolt to the specified torque.

9. Install the radiator fan impeller and shroud.

Models with automatic regulator

Reducing the tension of the auxiliary drive belt

To loosen the accessory drive belt tension on 6-cylinder DOHC engines, place a wrench on the tensioner pulley nut (1) and turn the wrench clockwise.

1. Remove the radiator fan impeller and shroud.

2. Place a spanner in the center of the tensioner pulley and use the spanner to turn the tensioner clockwise, which will decrease the tension on the auxiliary drive belt (see Fig. Reducing the tension of the auxiliary drive belt).

3. Secure the tensioner in this position with a wrench and remove the auxiliary drive belt from the pulleys.

4. Install the new accessory drive belt onto the pulleys, starting with the idler pulley and continuing in the sequence shown in the illustration Accessory Drive Belt Location on a 6-Cylinder DOHC Engine.

5. Release the wrench holding the tensioner mechanism, causing the tensioner mechanism to rotate and tension the accessory drive belt.

6. Install the fan impeller and shroud.

Checking the air conditioning system

Location of the inspection window for checking the fluid level in the air conditioning system

1. The air conditioning system pressure sensor is located on the side of the feed tank.

2. Turn off the ignition and disconnect the electrical connector from the top of the pressure sensor.

3. Start the engine in idle mode and turn on the air conditioning system on the instrument panel.

4. Wipe the viewing window located on the side of the feed tank (see picture).

5. Connect the electrical connector to the pressure sensor and observe the viewing window. This will activate the electromagnetic clutch and the refrigerant level in the viewing window should increase. The refrigerant visible in the viewing window should be free of air bubbles.

If the refrigerant level in the air conditioning system is too low or the pressure in the system is too low, the pressure sensor will prevent the air conditioning system from turning on. In this case, it is necessary to repair the air conditioning system in a specialized workshop.

Checking the oil level in the piston shock absorber (STROMBERG)

Unscrewing the inspection hole plug from the top of the STROMBERG carburetor

Topping up oil in the piston shock absorber of the STROMBERG carburetor

1. Unscrew the inspection hole plug from the top of the carburetor (see fig. Unscrewing the inspection hole plug from the top of the STROMBERG carburetor).

2. Check that the piston shock absorber oil level only reaches the top edge of the inspection hole.

3. If necessary, add oil to the lower edge of the inspection hole (see fig. Topping up oil in the piston shock absorber of the STROMBERG carburetor).

4. Screw the plug that closes the inspection hole.

Checking idle speed and fuel mixture quality

The adjustment must be made on a hot engine. All electrical consumers must be switched off and the radiator fan must not work.

Idle speed

Please note: On models with PIERBURG carburetors, idle speed is controlled by the electronic unit and cannot be adjusted manually.

Location of the adjusting screws of the STROMBERG carburetor

1. Connect a tachometer to the engine and check the idle speed. Adjustment is made by turning the idle speed screw (see fig. Location of STROMBERG carburetor adjustment screws).

2. Increase engine speed briefly and then re-measure idle speed.

CO content testing

Adjustment of CO content

To adjust the CO content, loosen the lock nut (1) and rotate the fuel shut-off valve (2).

1. Insert the exhaust gas analyzer into the exhaust pipe.

2. Increase engine speed to 2,000 rpm for 15 seconds, then return the engine to idle speed.

3. Check the CO content in the exhaust gases. To adjust, remove the plug from the fuel shut-off valve, loosen the lock nut and, by turning the fuel shut-off valve, set the required CO content (see fig. CO content adjustment).

Increased idle speed

1. Run the engine at idle speed. Check that the idle speed and CO content are adjusted correctly.

2. Manually open the throttle so that the engine runs at 2500 rpm. At the same time, insert a small screwdriver into the slot on the side of the throttle body, accessible after removing the plastic cover, and move the engine lever toward the engine until significant resistance is felt.

3. While holding the engine lever with a screwdriver, release the throttle valve. The engine should run at high idle speed.

4. Using a tachometer, check for high idle speed. To adjust, turn the idle speed screw. The high idle speed screw is the shorter of the two screws (see fig. Location of STROMBERG carburetor adjustment screws).

5. Finally, open the throttle valve briefly to disengage the idle speed increase mechanism and allow the engine to run at normal idle speed.

Checking CO content at high idle speed

Location of auxiliary air adjustment screw plug

1. Install the exhaust gas analyzer into the exhaust pipe.

2. Set the idle speed to high. Check the CO content in the exhaust gases. To adjust, remove the plug from the auxiliary air adjusting screw and, by turning the screw, set the required CO content (see Fig. Location of auxiliary air adjustment screw plug).

3. Finally, open the throttle briefly to disengage the high idle mechanism and allow the engine to run at normal idle speed.

Models with KE-GETRONIC fuel injection system

The adjustment must be made with the engine warmed up to normal operating temperature. The adjustment must be completed before the engine temperature reaches 100°C. On later models, the idle speed is controlled electronically and adjustment is not possible without special test equipment.

When making adjustments, the air filter must be in place with the vacuum hoses and crankcase ventilation hose connected.

Access to the idle speed adjustment screw

The idle speed adjustment screw is accessible through a recess on the back of the air filter housing.

Adjustment of CO content in exhaust gases

1. Install the exhaust gas analyzer into the exhaust pipe.

2. Start the engine at idle speed. On vehicles with automatic transmission, set the gear selector to the PARK position. Turn off all electrical consumers.

3. The idle speed adjustment screw is accessible through a recess on the back of the air filter housing (see Fig. Access to the idle speed adjustment screw).

4. Turn the adjusting screw to set the required idle speed.

5. Turn off the engine.

6. To adjust the CO content in the exhaust gases, remove the air cleaner housing and, using a lever, remove the plug, then reinstall the air cleaner assembly.

7. Start the engine and increase the engine speed to 2000 rpm for 10 seconds. Then set the idle speed.

8. Check the CO content in the exhaust gases. The CO content is adjusted by turning the mixture quality adjusting screw (see fig. Adjustment of CO content in exhaust gases).

9. Finally, remove all the gauges and install a new plug on the fuel mixture adjustment screw.

Checking the front suspension and steering

Checking the front wheel hub bearings for wear

1. Raise the front of the vehicle and support it securely on stands.

2. Visually inspect the ball joint dust boots and rack and pinion steering gear boots for cracks, wear, and aging. Any wear on these boots will result in loss of lubricant and entry of water and dirt, resulting in rapid wear of the ball joints or steering gear.

3. Check the power steering hoses for wear or deterioration, and the pipes and hose connections for leaks. Also check the steering gear boots for signs of pressure leakage, which indicates damage to the steering seal.

4. Raise the car with a jack, grab the wheel with your hands at the 6 and 12 o'clock positions and try to rock it in a vertical plane. A very small amount of play in the wheel is acceptable, but if the play is significant, further inspection is necessary to determine the source. Continue rocking the wheel while an assistant applies the foot brake. If the play is eliminated or significantly reduced, the hub bearings are likely damaged. If the play is still significant with the brake applied, there is wear in the suspension joint and mount (see picture).

5. Now take the wheel at the 9 and 3 o'clock positions and try to rock it horizontally. The presence of play in the horizontal plane can be caused by wear of the hub bearing or the ball joints of the steering rod. If the outer or inner ball joint is worn, the play will be obvious.

6. Using a large screwdriver as a lever, check for wear in the suspension mount bushings between the suspension component and the point of attachment. Some movement should be visible since the mount bushings are made of rubber, but excessive wear should be evident. Also check the condition of any visible portions of the rubber bushings for cracks, wear, and deformation.

Checking the shock absorber

Check the shock absorber for any signs of fluid leaks. If a leak is found, the shock absorber is damaged and needs to be replaced.

Attention! Shock absorbers must be replaced in pairs on one axle.

The effectiveness of the shock absorber is also checked by pressing on the corner of the body and releasing it sharply. The body should return to its original position after releasing it. If the body rises above the original position and continues to swing, then the shock absorber located on this side is probably out of order and must be replaced. Also check the shock absorber mount for wear.

Checking the drive shaft protective cover

Checking the condition of the protective boot of the constant velocity joint of the drive shaft

1. Raise the rear of the vehicle and support it on stands.

2. While rotating the rear wheel, inspect the rubber boots of the constant velocity joints by squeezing them to open the folds. Check for cracks that could allow grease to leak out, or water and dirt to get in (see picture).

3. Also check the condition of the fastening clamps, inspect the inner hinge covers and the covers on the other side. If any damage is found, the protective cover must be replaced immediately.

4. At the same time, check the general condition of the constant velocity joints by holding the shaft and trying to turn the wheels. Try again by holding the inner constant velocity joint and turning the shaft. Any noticeable play indicates wear in the joint, wear in the shaft grooves, or looseness of the shaft lock nut.

Checking the front brake pads

1. Apply the handbrake, raise the front of the car and secure it on stands. Remove the front wheels.

2. Check the thickness of the brake pads through the inspection hole in the front of the caliper.

3. If the brake shoe lining is worn to the minimum thickness, all four brake shoes must be replaced as a set.

4. Install the wheels and lower the vehicle.

Checking the rear brake pads

1. Raise the rear of the car and secure it on stands. Remove the rear wheels.

[Information copied from the website: mercedesman.ru]

2. Inspection of the brake pads can be done through the inspection hole in the top of the rear caliper. If the brake lining is worn to the minimum thickness, all brake pads must be replaced as a set.

3. Install the wheels and lower the vehicle.

Checking the exhaust system

1. With the engine cold, check the condition of the exhaust system along its entire length.

2. Check the pipes and their connections for leaks, corrosion and damage. Check that all brackets and suspension elements of the exhaust system are in good condition and evenly tensioned.

3. When moving the exhaust system of the car to the sides, make sure that it does not touch the car body. Otherwise, replace the rubber hangers of the exhaust system.

Checking the oil level in a manual transmission

Unscrewing the oil level check plug in a manual transmission

1. Place the car horizontally over the inspection pit. Check the oil level no earlier than 5 minutes after stopping the engine.

2. Clean the area around the transmission oil level plug. The oil level plug is located on the front right side of the transmission. Unscrew the plug and clean it (see picture).

3. The oil level should reach the lower edge of the oil level plug hole.

4. If necessary, add oil to the gearbox through the oil level check plug hole.

5. Tighten the gearbox oil level check plug to the specified torque.

Checking the oil level in the rear final drive

Unscrewing the oil level check plug in the rear final drive

1. Place the vehicle over an inspection pit or lift it on a lift.

2. Clean the area around the oil level check plug located on the left front side of the rear final drive. Remove the plug (see picture).

3. The oil level should reach the lower edge of the oil level check hole.

4. If necessary, add oil to the rear final drive through the oil level check plug hole.

5. Screw the oil level check plug into the rear final drive and tighten it to the specified torque.

6. Lower the car.