Why it is important to change spark plugs

A rattle sound means the insides are broken apart. If it’s clogged, the motor will run poorly and get very poor gas mileage.

Don’t panic. Here are five of the most common reasons why your check engine light might have come on in your Mercedes-Benz.

Check Engine Light Mercedes-Benz

1. Gas Cap

While your gas cap might not seem like the most important piece of equipment in your Mercedes-Benz, it actually carries a pretty important role. It maintains pressure in the engine and prevents fuel vapors from leaking out. In some cases the check engine light will come on when the gas cap is not tightly replaced. We suggest that you unscrew the gas cap and re-tighten until it clicks, then allow the check engine light up to a day to reset. A loose, broken, or missing gas cap can cause your vehicle to start jerking and lower its efficiency. If the light remains on after a day, take in to the service garage.

2. Oxygen Sensor

The oxygen sensor in your Mercedes-Benz monitors the percentage of unburned oxygen in the exhaust. Over time the sensor can get covered in ash; therefore, reducing its effectiveness and leading to a decrease in gas mileage and an increase in emissions.

3. Catalytic Converter

Your catalytic converter reduces exhaust gases by converting carbon monoxide and other harmful materials into harmless ones. Most failures are down to faults with other items, but a damaged catalytic converter can mean your car will fail its emissions test.

4. Mass Airflow Sensor

The mass airflow sensor allows your car’s computer to know how much fuel is needed based on the amount of air coming into the engine. Faults can decrease efficiency, increase emissions, and cause your car to stall.

5. Spark Plugs and Wires

Spark plugs and wires are responsible for creating the original spark that initiates combustion within your Mercedes-Benz, but they can fail over time. If yours are faulty, misfires will occur.

Your Mercedes-Benz Check Engine Light is never something you should ignore. While these reasons might not sound too serious, they can develop into a much more complex issue over time. See your mechanic.

Only a few general concepts, keep in mind that the exhaust gas recirculation (EGR) valve is an integral part of a vehicles emissions control systems. It operates under the premise of lowering combustion chamber temperatures to reduce the amount of pollutants created by the combustion process. Being closely tied to the combustion process, this valve's operation has direct effect on the overall performance of the engine. Poor or faulty operation of the EGR valve can result in several notable symptoms and leads to increased pollutant emissions.

Poor Idle: An improperly closing EGR valve will act as a vacuum leak, disrupting the correct fuel and air mixture, causing a lean mixture condition. This results in misfiring cylinders and poor engine idle.

Overheating: The basic function of the EGR valve is to introduce exhaust gases into the combustion chamber at specific and controlled rates, lowering combustion temperatures, and lowering pollutant emissions. An EGR valve that does not open properly fails to introduce sufficient amounts of exhaust gases, causing combustion chamber temperatures to rise, leading to overheating of the engine.

Poor Fuel Economy: A sticking EGR valve will not open and close at the proper rate, leading to a reduction in the efficiency of the combustion process due to the lean fuel-air mixture it causes. This results in the engine having to work harder to perform the same amount of work, requiring more fuel to do it. On-board computer systems can also try to compensate for this lean condition by introducing additional fuel to the mixture, further increasing fuel consumption.

Increased Emissions: EGR valves are designed to lower the emission of pollutants from the combustion process. This is done by lowering the temperature of the combustion process through the introduction of exhaust gases into the fuel and air mixture. Lowered combustion temperatures result in more efficient burning of the fuel and air mixture, and less pollutants in the exhaust emissions. An improperly operating EGR valve will not correctly lower combustion temperatures, causing noxious emissions to increase, which can cause a vehicle to fail emissions inspection.

Test cylinders compression and check if some fault code is stored in the PCM 9computer).

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 STEERING/FRONT SUSPENSION: CHECK
• Maintains integrity of steering and suspension components, and
assures proper wear
 REAR SUSPENSION: CHECK FOR WEAR
• Maintains integrity of suspension components, and assures
proper wear
 DRIVESHAFT JOINTS: CHECK FOR WEAR/PLAY
 DRIVESHAFT: CHECK BOOTS
• Assures proper wear and that foreign matter does not contaminate
drive shaft joints
 PROPELLER SHAFT, PILOT BEARING AND
UNIVERSAL JOINTS: CHECK WEAR
AWD models only
• Helps assure proper all wheel drive performance
 EXHAUST SYSTEM: CHECK FOR DAMAGE/LEAKS
• Maintains quiet operation and proper emission control
 SPARK PLUGS: REPLACE
Except engine VIN code 85
• New spark plugs are specially designed and calibrated to provide
optimum engine operation.
• Engine is tested on special Volvo equipment after spark plug installation

Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).

When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

Hope this help.