Auto Service World
Feature   May 1, 2014   by Tom Venetis, Editor

Just Because It Is Hidden, Does Not Mean It Can’t Be Checked

Spark plugs, O2 sensors and injectors might not be visible to the vehicle owner, but they still need to be checked

They are the hidden but critical components of an engine. The owner can’t see them and would be hard pressed to even point to where they are on some modern engines. But they know right away if something goes wrong with any of them as the vehicle’s engine does not operate properly.

One of the challenges is that with most vehicle technologies today these components are made to last longer and are more robust than their earlier incarnations. That is the result of two things: one is that the materials used to manufacture them are of very high quality and they are made to operate in smaller, more powerful engines, so they can withstand environments that would have toasted their earlier cousins. That being said, it does not mean they can be overlooked during a regular vehicle inspection.

Spark Plugs

It is a truism, but it needs to be said once more: spark plugs are often the most neglected components in an engine.

It’s hard to put an exact number on how overlooked spark plug maintenance is. One thing is certain, new vehicle technologies have now made it critical for technicians to use the right spark plug as a replacement, says Sukhneet Mavi, product manager with NGK Spark Plugs Canada Limited. “Most spark plug offerings since the mid-2000s are very specific to engine design and they are mostly double precious metal plugs, where both [the] centre and ground electrode are made of precious metals. These newer generation plugs do not require regular maintenance as their target service life is approximately 120,000-160,000 kms from installation; but due to the harshness of some engine designs, this service life is affected dramatically. For optimum performance from the vehicle, it is critical to follow the recommended change interval when using the OEM type or follow the parts manufacturer’s service interval when using the aftermarket OEM equivalent offerings.”

“The short answer is that spark plug maintenance is probably often overlooked until the ‘Check Engine’ light is on,” agrees Jeffrey Boehler, chief engineer at Autolite, a Fram Group Company. “For most automotive applications on the road today, the recommended service interval for original equipment spark plugs is 160,000 kms. However, an important footnote to this is usually something like ‘for normal service.’ Things like stop-and-go city driving, lots of idle time, heavier engine load or high speed driving would all be exceptions to the category of normal service. For this reason, there are many situations where the spark plugs may need to be changed sooner than the recommended interval.”

While spark plugs may have extended service life, technicians and spark plug makers all agree that regular visual inspection of the plugs is still a crucial part of a regular maintenance regime.

“One of most important signs to look for is the condition of the centre and ground electrodes,” says James Miyamoto, senior product specialist, powertrain product management with Denso Corporation. “Check the gap between the electrodes to see if it is within original equipment specifications. Oxidation from extreme temperatures and pressures, along with wear from intense voltage, will erode the electrodes which may increase the gap. When the gap increases too much, it increases resistance which makes for a weaker and inconsistent spark, therefore decreasing engine performance.”

Visual inspection is particularly important with direct injection engines as problems with spark plugs will impact engine performance. As well, replacing a spark plug with a non-OE specific spark plug can also cause problems.

“It is very important to check spark plugs by the recommended intervals stated on the OEM service manuals,” adds Miyamoto. “An issue that technicians need to be aware of is that downgrading spark plugs from OE-specifications can significantly alter the vehicle’s performance, fuel economy, and replacement interval. For example, a vehicle that comes equipped with a long life Iridium spark plug should not be replaced with a lower specification metal technology spark plug. Due to the ever increasing government standards for emissions, consumer demands for increased performance without sacrificing fuel economy, direct injection and forced induction systems are becoming very popular. To maintain the optimal engine efficiency, it is even more important to install a high quality OE specification spark plug or better. “

Tim Stumpff, product manager, spark plugs with the automotive aftermarket division of Robert Bosch, adds that with direct injection engines it is important to make sure the spark plugs are put in correctly as well, since the “spark plugs have to be installed in the engine perfectly to ensure proper engine performance. If the spark plug is installed so that the ground electrode blocks the injection , the fuel won’t be ignited by the spark and will cause a misfire. To ensure this does not happen, it is critical that the spark plug is tightened to the correct torque specifications not only so it stays tight in the cylinder, but also so that the ground electrode is in the correct position to allow for ignition to occur.”

What needs to be emphasized to vehicle owners is a variation on the old saying that the eyes are the windows to the soul – in this case, the spark plug is a window to the health of the engine.

“Spark plugs . . . can be a valuable diagnostic tool,” says NGK’s Mavi. “The condition of the spark plug firing end displays the condition inside the combustion chambers and can be helpful in exposing underlying fuel trim and/or ignition system problems. Any experienced tuner can use spark plugs to find the root cause of problems, determine air-fuel ratios and to increase vehicle performance. The overall appearance and colour of the spark plug firing end can reflect the accuracy of spark plug heat range and/or ignition timing. The quantity and chemical make-up of the deposits can reflect the underlying fuel trim problems. The deposits near the electrodes largely affect the spark plug operation and if they become conductive, for example, the insulation resistance drops to zero, the plug short circuits to ground and causes the misfire condition.”

“If the engine is running OK, the most important things to look at would be the spark plug electrodes for wear and the insulator tip for any build-up of deposits on the surface,” adds Fram’s Boehler. “The condition of these parts of the spark plug can tell you if any conditions of overheating are occurring that could lead to pre-ignition and possible engine failure. The deposits on the insulator tip surface can indicate if there are any problems with the engine such as excess oil consumption due to wear, fuel system problems, etc.”

Boehler makes a point of adding that the higher performance engines in use today often run at conditions that result in higher electrode temperatures and higher required sparking voltages for the spark plug. These types of conditions can increase the wear rate of the spark plug electrodes. For these reasons, it is important that the spark plug inspections include a measurement of the spark gap as well as a visual inspection of the electrodes for any abnormal wear or corrosion as well as evidence of overheating.

“These harsh environments push the innovation required to survive to another level,” Boehler concludes. “From new material development, to designs that provide greater mechanical, electrical, and thermal robustness, we are developing concepts and hardware for racing that help us to prepare for the future of OE automotive, which is higher power density in smaller diameter spark plug packages.”

Oxygen Sensors

Here is a question: When do most people change their oxygen sensors? The answer is not often or not until the ‘Check Engine’ light comes and the owner brings the car in to be inspected. Still, it must be kept in mind that the ‘Check Engine’ light does not necessarily mean there is a problem with the oxygen sensor.

“There are other engine management sensors that may trigger a check engine light and cause an oxygen sensor to measure readings that are too lean or too rich,” says Sean Lappin, senior product manager, oxygen sensors, gasoline systems group, automotive aftermarket division, with Robert Bosch. “Technicians should look for other common symptoms such as poor gas mileage, rough idling, poor performance and/or a possible misfire. Technicians should also utilize an OBDII scan tool to pull trouble codes from the vehicle’s ECM and also monitor O2 sensor outputs when trying to diagnose an O2 sensor issue.”

“For any vehicle made after 1996, O2 sensors are easy to diagnose,” says Frank Guarino, global chief engineer, powertrain and thermal with Delphi Product & Service Solutions. “The onboard diagnostic system will tell you when an O2 sensor is not functioning by setting a MIL light, or ‘Check Engine’ light, and by setting an appropriate DTC (diagnostic trouble code). Vehicles made prior to 1996 are a bit trickier. You should refer to the service manual to diagnose an O2 sensor issue. “

NGK’s Mavi adds that a common issue with oxygen sensor diagnostics and maintenance is that misdiagnosis of the sensor often comes from neglecting to check for software updates, as software issues can sometimes be the root cause of what is mistakenly thought is a failed oxygen sensor.

“What we see as an OE supplier in the sensor category is that the repair is becoming far more extensive than simply changing the failing part,” Mavi continues. “On many late models, the repair is not complete until the technician checks for and addresses manufacturer TSBs, which may include a PCM re-flash to fix calibration or other software issues.

“Many technicians are familiar with Mode 6 diagnostics and hopefully they are using the data to verify a repair, but it is imperative to first ensure that proper drive cycle conditions and/or cold soak periods (if necessary) are met, otherwise the new part changed may still register a ‘fail.’ In addition, often components or subsystems may not immediately set a fault code, but can still affect vehicle drivability. Therefore, even though an oxygen sensor or other emission component is operating within its set high and low limits, it does not mean it is operating effectively and may be about to fail.”

Jannivine Leung, senior product specialist, powertrain product management with Denso Corporation adds that today’s new engine designs and the growing number of direct injection engines means technicians will have to make a point to regularly inspect oxygen sensors. The reason is that these sensors are now more critical than ever to the smooth operation of direct injection engines and for meeting stringent emissions and fuel efficiency targets.

“Today’s vehicles are equipped with more advanced oxygen sensors than sensors on vehicles built a decade ago,” Leung continues. “Today’s oxygen sensors have faster light off times to achieve closed loop more efficiently. They have been incorporated into multiple locations on a vehicle, therefore increasing feedback readings to the ECU. Most vehicles today will feature heated narrow band sensors and wideband or air/fuel ratio sensors together. The wideband and air/fuel ratio sensors were developed to monitor and control the air-fuel ratio, allowing for true emissions control versus narrow band oxygen sensors which only monitored and produced readings of rich or lean. Using a light bulb analogy, the oxygen sensor sends voltage and functions like an on/off switch, while the air/fuel sensor acts similar to a dimmer switch controlling the air-fuel ratio.”

One question that is often asked is how often should oxygen sensors be replaced? Because most vehicle owners almost never ask for them to be replaced unless they fail, the assumption by many is just that – replace them only when they fail. The reality is more complex, suggests NGK’s Mavi who points out that driving habits, vehicle use and maintenance history all affect the service life of oxygen sensors.

“For this reason, manufacturers typically adhere to suggested guidelines for possible replacement of oxygen sensors, often based on the type of sensor,” Mavi adds. “In fact, most oxygen sensors are only replaced once the MIL or ‘Check Engine’ light has come on and/or a drivability problem exists. Mode 6 can actually be a helpful tool in predicting life expectancy of a component. For example, if you had a vehicle with a P0136 DTC, you could also look at the other oxygen sensors on the vehicle, noting response time(s) and come to the conclusion that they are at or nearing the end of their life expectancy.

“In that example, if the result proved to be a faulty B1S2 (Bank 1 Sensor 2), a technician could offer their customer a scanner printout of their findings and suggest replacement of the other oxygen sensor(s) on the vehicle as preventative maintenance.”

“The O2 sensor pigtail, connector and wiring harness should be inspected whenever the car is on a hoist, for example during an oil change,” suggests Delphi’s Guarino. “If there is any sign of abrasion forming on any of these three supporting subcomponents, then the problem should be remedied to avoid further damage. Additionally, if the car is made after 1996, no further inspection or replacement is needed unless a check engine light comes on and an O2 specific DTC is stored by the OBD II system (read by a hand-held scan tool connected to the LDL port). If the car is older than 1996, and the car has experienced a noticeable loss in fuel economy, then the service manual diagnostic tree should be followed to see if the O2 sensor(s) need to be replaced.”

Fuel Injectors

One might think that with today’s high-quality fuels, fuel injector failure is a thing of the past. It is rare to find poor quality fuel today, as all the major fuel blenders follow strict guidelines for maintaining fuel integrity. Fuel contamination issues are more often caused by poor storage or vehicle fuel tanks filled with debris due to age.

Stephen Albert, product manager with ignition systems and engine management, automotive aftermarket division with Robert Bosch says, “the most common reason for injector failure is poor fuel quality, contamination in the fuel system, failure to replace the fuel filter and a poor electrical system which does not send adequate power to the injector. When any of the above are affected, it can result in some of the following: poor drivability, cold or hot start problems, increased fuel consumption and, in some cases, major engine damage due to contaminated oil.”

Ethanol is another issue, especially with some fuels using up to 10 per cent or more in the fuel mix.

“Ethanol is a serious solvent, degreaser or cleaner,” points out Denso’s Steven Gonzales, product manager, powertrain product management. “Ethanol scours and scrubs varnish, gum, sludge and dirt deposits out of a fuel system. The deposits will be ‘held’ in suspension in the ethanol fuel and will eventually wind up in the fuel injectors, and can choke off an engine’s fuel supply by clogging the injector.”

“Ethanol is a very corrosive fuel, so ethanol compatible injectors must be built to withstand the corrosive nature of the fuels,” adds Delphi’s Guarino. “Usually, an ethanol compatible injector will have different O rings at the interfaces where the fuel may come in contact with any part of the injector. When a technician services ethanol fuel injectors it is necessary to make sure that they are using ethanol compatible O rings. These are usually part of a service kit especially for the ethanol injector.”

“[Direct injection] injectors themselves are considerably different from PFI injectors in appearance,” he continues. “They are very narrow at the point where they sit in the cylinder head. Inspecting these injectors on the vehicle can sometimes prove to be difficult because they are mounted deeply into the cylinder head. Special service precautions and service tools are needed to service a GDI injector.”