Part Focus: Electrical, Engine Management / Brands: Lucas, Volt
Electrical and engine management specialist Lucas provide a knowledge drop and address common problems.
CRANK/CAMSHAFT SENSOR
The Camshaft Sensor monitors the positions of the camshaft to allow for correct ignition timing. The Crankshaft Sensor detects the position of the crankshaft allowing the ECU to calculate its position in relation to the pistons in the engine.
A weak signal from a faulty sensor results in loss of engine power or misfires. If the sensor has no output then the car will fail to start.
EGR VALVE
The Exhaust Gas Recirculation Valve helps the engine to more efficiently and completely burn fuel by recirculating a portion of the exhaust gas and running it through the combustion process again. Resulting in a cooler, more complete burn of the fuel which decreases harmful emissions.
A faulty EGR can result in loss of engine power, stuttering, jumping, black smoke from the exhaust or the car falling into ‘limp mode’.
COOLANT TEMP SENSOR
The Air Temperature Sensor is a thermistor that monitors the temperature of the air flowing into the engine. The sensor can also be used to monitor interior and exterior air temperature as part of the vehicle comfort settings.
Should this sensor fail, the temperature gauge may be incorrect. Fuel economy may rapidly decrease and engine backfires and cut outs are
common symptoms.
COOLANT TEMP SENSOR
The Air Temperature Sensor is a thermistor that monitors the temperature of the air flowing into the engine. The sensor can also be used to monitor interior and exterior air temperature as part of the vehicle comfort settings.
A faulty sensor can lead to increased cranking time when the engine is cold, poor fuel economy and a high nitrogen oxide reading.
AIR MASS METER
Air Mass Meters (AMM) also known as Mass Air Flow Sensors (MAFS) are fitted after the air filter but before the engine for smooth and fuel efficient operation. The sensor determines how much air is coming into the engine, helping it to decide the level of fuel needed for proper ignition.
Poor performance and rough idle are common symptoms of a faulty Air Mass Meter.
KNOCK SENSOR
The Knock Sensor is mounted on the engine block and acts like a microphone, transforming the vibrations caused by the sound waves from knocking into a voltage signal that can be read by the ECU. Knocking is continually monitored and ignition timing is retarded when required to prevent possible engine damage.
A faulty Knock Sensor can result in poor acceleration and reduced fuel economy.
AIR TEMP SENSOR
The Air Temperature Sensor is a thermistor that monitors the temperature of the air flowing into the engine. The sensor can also be used to monitor interior and exterior air temperature as part of the vehicle comfort settings.
A faulty sensor can lead to increased cranking time when the engine is cold, poor fuel economy and a high nitrogen oxide reading.
MAP SENSOR
The Manifold Absolute Pressure Sensor (MAP Sensor) determines the correct air/fuel ratio in vehicles which do not have an Air Mass Meter. They use air temperature and engine speed to determine air density and in some vehicles, measure EGR valve performance or monitor air pressure in turbo applications.
A faulty sensor could result in irregular engine RPM due to incorrect readings or turbo failure.
IGNITION COIL
The Ignition Coil is essentially wire wrapped around a core to make a transformer. This transforms the battery’s low voltage to the thousands of volts needed to create an electric spark in the spark plugs and ignite the fuel. A low voltage input on the primary winding then creates a high voltage output on the secondary winding.
Look for misfires, stalling or failure to start.
THROTTLE POTENTIOMETER
The Throttle Potentiometer is a variable resistor fitted onto the throttle body on the shaft of the throttle valve. It monitors the position of the valve and therefore how much air is being drawn into the engine. Allowing correct operation of the Idle Air Control Valve when the accelerator is not being pressed.
Poor idling, misfires, stalling or hesitation could be symptoms of failure.
IGNITION COILS
The iconic Lucas brand has been igniting our engines for over a Century and Lucas coils in one form or another have been a consistent presence on our vehicles. In this TechAssist bulletin we offer general tips and advice for replacing ignition coils and highlight some more product specific fitting issues.
When replacing ignition coils Lucas recommend ensuring the following checks are made.
Check all spark plugs for damage, gap and/or wear. Ignition coil failure is commonly caused by voltage overload due to bad spark plugs. Not replacing them could cause the new coil to fail prematurely.
Always ensure that spark plugs are reinstalled correctly after completing checks.
Ensure that the new coil is seated correctly. This is particularly important for rail coils as if it is not, the coil may bow or crack when bolted down.
Complete final checks, clear the fault codes and update the ECU.
Lucas DMB813 Ignition Coil (Rail)
The Lucas DMB813 rail coil is amongst the most popular in our extensive range, fitting popular Citroen and Peugeot vehicles. It is also one of the most commonly returned due to incorrect fitment. The issue arises when springs are inserted into the rubber boots in the incorrect direction. As part of our continuous product development program, newer versions are pre-assembled to eliminate such issues. However when fitting non-assembled units the following guidelines (right):
EGR VALVES
We look at how the EGR valve works, the causes and symptoms of failure and how to ensure longevity of the replacement valve.
What is it for?
Fundamentally the EGR valve reduces harmful nitrogen oxides (NOX) emissions from our exhausts.
How does it work?
NOX is produced when combustion temperatures exceed 2500°F and nitrogen begins to react with oxygen. The EGR valve helps keep temperatures below the NOX threshold by recirculating a small amount of exhaust gas back through the combustion process. This dilutes the incoming air/fuel mixture and cools combustion temperatures resulting in reduced NOX emissions.
Why does it fail?
The most common cause of EGR valve failure is carbon deposits that cause clogging or sticking. The valve may stick open or closed.
Symptoms of failure
If the EGR is stuck in the open position, a continuous flow of exhaust gases will be sent back to the inlet manifold resulting in a rough idle when the engine is cold and stalling when the engine idles. Fuel economy will decrease and you may notice an increased smell of fuel. Lower temperatures caused by continuous recirculation can increase emissions resulting in MOT failure.
If the EGR is stuck in the closed position, fuel may ignite early as it reaches higher temperatures and a pinging or knocking may be heard from the engine at low RPM. Loud detonations may be heard when a second ignition happens, this can cause serious engine damage. Higher temperatures resulting from no recirculation will increase NOX emissions and may cause MOT failure.
In both cases, the engine check or malfunction indicator light may switch on.
REPLACING EGR VALVES
Remember these three steps to ensure the new EGR valves performs and lasts as expected.
1) Clean the system
Before replacing the EGR valve ensure that the system is cleaned. This step is commonly overlooked and a clean EGR valve is put on to a dirty system. The existing carbon deposits quickly re-contaminate the valve causing premature failure. We recommend using an EGR/Turbo cleaning aerosol to clean the combustion chambers and ducting to the EGR valve. Always follow the instructions given on the cleaning product. Variable-geometry turbocharger systems should also be cleaned as carbon fouling here can also contaminate the EGR valve. Heavily contaminated systems would benefit from a more thorough clean using a Terraclean or similar system.
2) Replace the EGR valve
Once the system is clean, the new EGR valve can be fitted.
3) Reset the ECU
This will ensure that the ECU recognises the new component and that it operates correctly.
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