Auto Service World
Feature   May 1, 2012   by Nestor Gula

Keeping it Clean

Making sure O2 sensors and spark plugs are maintained will keep a vehicle's emissions controls and nature happy

I had an old, but dearly loved and cherished, beater when Ontario introduced the Drive Clean program in 1999. I admit I was nervous as I was not too sure that it would pass, and I was not sure I wanted to sink too much money into the vehicle.

It passed with flying colours and my service provider explained to me that this was due to the fact that I did regular maintenance on the sparks plugs, oxygen sensors and wire sets.

This 1987 S10 Jimmy had a 2.8litre V6 with throttle body injection. Compared to modern cars it was positively cro-magnon. But it still got good fuel mileage. Back then, I was swapping spark plugs and wire sets about every two years, while my current vehicle has been purring cleanly and efficiently now for about 12 years with but one change of plugs and wires.

Designs of engines and all their components have improved remarkably. “New engines, especially those utilizing Gasoline Direct Injection (GDI) and turbochargers, require significant changes in OE spark plug design,” according to Mark Wilkinson, group product manager, Spark Plugs for Bosch. “Vehicle manufacturers have focused on exact ‘spark projection’ and the use of precious metals with appropriate new assembly processes to create the best spark in the latest generation of engines. ‘Spark projection’ refers to the actual location of the spark plug in the combustion chamber.”

A major change to spark plug design has been the introduction of precious metals to this product. “Over the years we are seeing more use of precious metals in spark plugs. What this means is a longer service life,” said Sukhneet Mavi, product manager for NGK Canada. “Most spark plugs now last about 160,000 kilometres. Design is evolving as well because of higher compression engine – plugs are becoming longer and thinner. We have to use newer materials that can stand up to the higher temperatures and the higher compression.”

It is still important to change plugs according to the manufacturer’s specification. “Some still have to be swapped out every 40,000 kilometres,” stated Mavi. “It goes with the OEM recommendation when to change the plugs.”

Wilkinson notes that, “Bosch works closely with vehicle manufacturers to develop and improve spark plugs for their vehicles, and transfers this knowledge and expertise to the spark plugs produced for the replacement market.” In general he said that, “advanced technology and spark plug design, combined with the greater use of more durable materials and improved manufacturing techniques translates into longer spark plug life.” And this keeps the sparks in the engine at their optimal level.

A strong spark from the spark plug can only be achieved if there is enough electricity going to the spark plug. Spark plug wires should be replaced as recommended by the OEM. Some customers might question this move, but spark plug wires do have a hard life. They carry serious amounts of electricity in very short bursts and exist in a very difficult environment. “The ignition wires are routed very tightly around the engine there is a lot of humidity and experiences a range of temperature hot and cold,” said NGK’s Mavi. Most manufacturers recommend replacing them every five years or 100,000 kilometres according to Mavi. “The ignition wires are made of a porous material like a silicone jacket. It is hard to see or notice the cracks in the material,” he said. “Moisture starts to seep in and they will lose their ability to carry electricity efficiently. They will still work but not at optimum capacity.”

In my ’87 Jimmy, if the engine warning light came on, I more or less knew that one of the oxygen sensors had gotten fouled and needed to be replaced, a simple fix back then. Newer cars need more attention. “If the ‘check engine’ light is on and flashing, this means it demands immediate attention,” said Warren Suter, director, Engine Management Systems, Bosch Automotive Aftermarket. “A worn out oxygen sensor often is the culprit and changing it may cost a lot less than replacing damaged engine components. But before just replacing the sensor and sending the vehicle back out, check to see if engine problems may have caused the sensor to fail. A blown head gasket, for instance, could be allowing antifreeze to leak into the cylinders and into the exhaust stream, which can kill the oxygen sensor.

If not corrected, this problem would cause the replacement sensor to fail, bringing the vehicle back with an unhappy customer. The vehicle’s oxygen sensor measures the amount of oxygen in the exhaust and signals the engine’s computer to adjust the air-fuel ratio to ensure that combustion is as complete as possible. If the oxygen sensor is worn out and fails to assess the air-fuel ratio accurately, the engine’s computer tries to accommodate the perceived variation and, in the process, may adjust the mixture too lean or too rich.”

A potential result of an engine’s sensors providing faulty information to the engine management system is possible damage to the catalytic converter or other major components. It also can add up to higher fuel mileage and a failed Drive Clean examination.

Once the sensor is removed it should be tested to see if it is really at fault. “Fault (error) codes do not necessarily indicate that a sensor is faulty,” said Dave Ehle, global chief engineer, vehicle electronics and thermal, Delphi Product & Service Solutions. “When a vehicle’s engine management system detects a fault related to a given sensor, a fault code is stored in memory and freeze-frame data is stored in memory. The code provides us a description of the fault and where it is located in the engine management system. The system reports a given condition has been detected within a circuit, but the system does not identify which part of the circuit is faulty.”

Sensors have become hardier to avoid the hassles of errors in fault codes. “Oxygen sensors have been made tougher and more resilient to fouling and denigration by means of a porous ceramic coating which is deposited on the surface of the sensing element exposed to the exhaust gas during the manufacturing process,” said Ehl. “This coating prevents contamination and erosion of the element from particulates and combustion residue from the exhaust stream, while allowing oxygen to permeate through to the electrode surface.”

“They have a life of 30,000 to 100,000 miles depending on the driving and engine condition, said Robert Hall, OTC technical sales manager. “The oxygen sensor signals the computer if the air/fuel mixture is too rich or too lean in order for the computer to properly adjust the mixture. As the O2

sensor goes bad, it will slow down in its reaction rate or give false readings causing the air/fuel mixture to be incorrect.” The sensor is used by the vehicle’s engine management system to determine proper ignition timing and air/fuel mixture. “If the mass air flow sensor goes bad, gets dirty or gets fouled by oil film, the computer will get a incorrect reading of the amount of air being consumed by the engine,” said Hall. “As with any computer, the engine computer must have the correct input data or it will not run right, garbage in garbage out.”

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