AfterMarketNews Auto Care Pro AutoProJobs Auto-Video.com Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service

Second-rate parts mean second-rate results

When it comes to diagnosing a problem, one of the biggest mistakes is thinking that the problem is gone after you’ve installed a new part. I’ve had vehicles brought in countless times with the same old story attached to them. The customer will say:...

Read more...

GearWrench Launches Street Team, a New Mobile Driver Program

GearWrench, a premier hand tool brand from Apex Tool Group, has announced Street Team, a new program that gives independent mobile distributors the support of an established tool brand without the restrictions of a franchise. "Response to the program...

Read more...

AUTO 7 Named Approved Vendor For Automotive Parts Associates

Steven Kruss, president of Auto 7, which supplies Korean-made, OEM-quality automotive parts to distributors across North America, announced that Auto 7 has been named an approved vendor of Automotive Parts Associates (APA), one of the nation’s...

Read more...

Internal Engine Oil Consumption Diagnostics

Due to the variables in engine design and ­operating conditions, internal engine oil ­consumption complaints are often the most difficult to solve. In some cases, oil consumption might be more severe under low-speed operation, in other cases, high-speed...

Read more...

Hyundai Fuel System, Emissions Diagnostics

Hyundai has done a good job of improving its ­offerings over the years from both an aesthetic and mechanical viewpoint. Complemented by a strong warranty and good value, the carmaker has been able to increase its market share year over year. If you aren’t...

Read more...

Curing Volvo Manual Transmission Rattle

In an effort to increase fuel efficiency, today’s engines produce more torque so they can be ­driven at extremely low rpm. ­Reduced viscosity engine and gearbox oils, less vehicle weight and improved aerodynamics also contribute to better fuel economy....

Read more...

Servicing The Electronically Adjustable Shocks Of Full-Sized GM Trucks

Since the 2000 model year, GM has offered electronically adjustable suspension as an option on Chevy, Cadillac and GMC full-size trucks. The system actuates the valving in the shocks to control ­suspension position and body attitude. The electronic...

Read more...

Diagnosing Clutch Assembly Noises

Noise can resonate from many areas of a ­vehicle’s driveline. There are several types of noises associated with the clutch assembly. The release bearing is most often blamed for being the cause of noise when, in many cases, it is not the release...

Read more...

Making Sense Of Steering Angle Sensor Input And Data

Measuring the­ ­position angle, rate of turn and force of the steering wheel is critical for Electronic Stability Control (ESC) systems. Scan tools call these Steering Angle Sensors (SAS) and typically display the information in degrees. The SAS...

Read more...

Victor’s Cash Back Program Makes Select Welders and Plasma Cutters More Affordable

Victor Technologies has launched its Cash Back Rebate program for customers in the United States and Canada. Between July 1 and Dec. 31, 2014, purchasers of select Tweco and Victor Thermal Dynamics systems can receive between $50 and $450 cash back....

Read more...

AVI To Provide Technicians with $1 Million in Free Training

AVI (Automotive Video Innovations) is giving back to the automotive community that has given so much opportunity to the Florida-based video company. To carry out that mission, AVI reports that it is pledging to give away $1 million worth of training...

Read more...

GearWrench Launches Street Team, a New Mobile Driver Program

GearWrench, a premier hand tool brand from Apex Tool Group, has announced Street Team, a new program that gives independent mobile distributors the support of an established tool brand without the restrictions of a franchise. "Response to the program...

Read more...

Home Emissions The Ins and Outs of Variable Valve Timing (VVT) Systems and Their...

Print Print Email Email

By the early 1990s, almost all import automotive manufacturers had a successful variable valve timing (VVT) system in production. These systems offered higher performance from smaller displacement engines at higher rpm.

As these vehicles exceeded their new car warranties, technicians learned the ins and outs of these systems and how regular oil changes could increase the life of VVT components. Now, the VVT is playing a direct role in vehicle emissions and the way gases are burned in the combustion camber.

These systems are simple from a diagnostic perspective. Most VVT components are non-serviceable and have integrated sensors. But, they are part of a larger diagnostic picture that includes everything from the throttle body to the oxygen sensor.

On a conventional engine, both the exhaust and intake valves’ open or closed position depends on their fixed position relative to the chain or belt that’s driven by the crankshaft. The pattern and timing cannot be altered, so there’s no way to increase or decrease the amount of valve lap when both valves are open at the same time.

As engines go, some have great low-end performance, while others have better top-end performance. (If you’ve ever heard an old street rod or dragster popping and rumbling at an idle, you’ve heard the lope from the cam. Because these engines are designed to have maximum performance at the top end, the cam is “cut” for better performance at the high end, so sacrifices are made at the idle end.)

With VVT, the valve duration can be matched to the engine speed, torque requirements and valve overlap. Now an engine can produce both low- and high-end performance without any erratic idle condition or high-end loss. This also enables an increase in miles per gallon throughout the engine’s power band by controlling valve timing and making the engine more fuel-efficient.

One great advantage of the VVT system is the way it can take the force needed to expel the burnt mixture out of the exhaust valve. Pushing the exhaust gas out of a cylinder requires some of the force that is generated during the combustion stroke. Opening the exhaust valve when there is still some pressure left in the cylinder allows a small portion of the exhaust gas to escape before the piston starts its upward travel. This reduces the exertion from the crankshaft and piston and provides a smoother, more even-running engine at every rpm level.

Leaving the intake valve partially open at the right point also allows fresh air to enter the cylinder while the exhaust valve is doing its job of removing the ­already-burnt gases. This slight intake valve opening creates low pressure and aides the piston in pushing out the remaining gases and getting ready for the next turn of the crankshaft. This is all the result of the configuration and shape of the exhaust ports and manifolds, all of which work together and make the whole process seamless.

EGR AND VVT

One item that’s going the way of the smog pump is the Exhaust Gas Recirculation (EGR) valve. The elimination of the EGR valve is the result of the VVT’s ability to control gases entering and exiting the combustion chamber. 

EGR systems are designed to reduce smog-causing nitrous oxides (NOx) by recirculating a portion of the exhaust gases from each cylinder of the engine back into the intake manifold. This process lowers the combustion temperature to under 2,500° F, above which NOx gases are formed, hurting both the environment and a ­vehicle’s performance.

EGR systems work, but they are not able to react fast enough or precise enough for modern engines and emissions standards. Modern VVT systems are doing the same job as the EGV valve, only better.

A VVT system is able to control the timing of the exhaust valve so that the right amount of inert ­exhaust gases remain in the combustion chamber for the next combustion cycle. This controls combustion temperatures and the production of NOx.

If you encounter a vehicle that has higher than normal NOx levels, or a burnt or damaged pre-catalyst, make sure the VVT solenoid and exhaust camshaft position sensor are operating properly.

HONDA’S i-VTEC SYSTEM

Honda’s term for a variable valve system is i-VTEC. The i-VTEC system uses an oil pressure solenoid activated electrically by the PCM to allow oil to pass into the rocker arm between the two normal rockers. This, in-turn, “locks” the normally used two intake valves together with a set of pins that are pushed outward into the two intake rockers and transfers their motion to a higher eccentric lobe (operated by the middle rocker arm). This higher lobe gives the engine the needed boost in power at an rpm higher than 4,500. 

When the rpm level drops below 4,500, the oil pressure solenoid shuts off, blocking off the oil pressure and returns the engine to the normally operated two intake valves.

The 2008 Accord takes this to a whole new level of valve control, allowing the engine to go from six cylinders, down to four, and even down to three cylinders. It uses a solenoid to “unlock/lock” the cam followers on one bank and allows the followers to float freely while the valve spring keeps the valve in the closed position.

Vehicles equipped with Honda’s VCM (Variable Cylinder Management) systems also include Active Noise Cancellation (ANC) and Honda’s Active Control Engine Mount (ACM) system. The ANC and ACM systems work in cooperation to cancel both noise and vibration that could occur in relation to the cylinder deactivation process.

The ANC system uses the audio speakers to cancel out noise by incorporating an opposite phase sound. This whole process is controlled by the ­computer ­system and becomes imperceptible to the driver. These systems use a mechanical/electrical ­solenoid that operates with oil pressure to accomplish the range of variable valve timing.

The VTECE system is slightly different in its ­configuration than the VTEC. The emission qualities have been increased but, at the same time, it ­performs the same functions as the VTEC system.

TOYOTA’S VALVEMATIC SYSTEM

Toyota came out with the Valvematic system in 2008. This system uses an intermediate shaft to achieve a continuous variable valve lift. The intermediate shaft consists of followers on either side of a roller bearing. These followers rotate with respect to the roller member and “finger followers” (small followers) by means of an internal gear and electric motor attached to the shaft. As the shaft moves, the roller member and followers will move in opposite directions (either closer or farther apart). As the angle increases, so does the valve lift. This system can vary the valve timing to any angle needed.

In 2007, the VVT-ie system was introduced on the Lexus LS460. This system is both electrical and hydraulic. The exhaust valve is still controlled by way of an oil pressure solenoid, while the intake is controlled by an electric motor on the front of the cam. This allows valve timing to be adjusted with no regard to engine temperature or oil pressure.

COMMON VVT PROBLEMS

The two most common codes I’ve run across are P0011 and P0021 (Camshaft position sensor “Bank 1” and Camshaft position sensor “Bank 2,” respectively). These codes (like any code) don’t entirely mean the sensor is faulty, however the diagnostic charts will tell you to look at the VVT system for a fault and check the sensor as well. Some of the common areas to look into are: valve timing, oil control valve, oil control valve filter screen, camshaft timing/gears, and, of course, the electrical side of the operation as well as the PCM.

The very first thing I do before turning nuts and bolts is to check the oil. Oil is an essential part of most VVT systems. Dirty oil and the lack of regular oil changes can leave a buildup of sludge or debris in the passages that lead to the pressure control valve that operates the variable valve timing. If the oil is dirty and too much sludge accumulates at the valve ports, the sludge can be passed on through the cam and the valve assembly. 

Then, the oil passages in the cam can be compromised and could result in a cam failure due to scored journals. Keep in mind that the VVT system is not operated at a normal driving condition rpm. For ­example, the Honda VTEC system doesn’t operate below 4,500 rpm. So, if you have someone who never gets the car out on the highway and never changes the oil, you can have a potential problem waiting to happen, if and when the car is revved up above 4,500 rpm the next time it heads onto an on-ramp of the local interstate highway.

Code P0521 (Oil pressure sensor/switch range/performance) could be an indication of the quality of the engine oil. It might not be the best diagnostic answer, but when I’ve seen this code on several vehicles, the oil was black and neglected. In some cases, the code can also indicate  that the wrong type of oil has been used. I wouldn’t use this as the final solution to the problem with variable valve timing, but rather an indication of things to come.

Lack of regular maintenance seems to be the big factor in most of these systems. Unlike vehicles from years gone by where certain maintenance issues could be neglected, these newer engines and newer systems ­require the utmost in care. Stressing this point to your customers and performing the required basic maintenance per the manufacturer’s schedule will safeguard their vehicle and increase your profits.

FUTURE OUTLOOK

In my opinion, VVT will be as common as a spark plug in the near future. Reducing emissions and ­reducing the need for an EGR valve, improving fuel economy and getting more performance out of smaller engines tells me that the VVT systems are here to stay. 

The next generation of VVT systems are on the drawing boards now, and it won’t be long before they’ll be in the marketplace. With the latest requirements in fuel economy emerging, engines with variable valve timing will become the norm, so it’s time to get ahead of the curve now.

The following two tabs change content below.

Scott Gonzo Weaver

Scott “Gonzo” Weaver is the owner of Superior Auto Electric in Tulsa, Okla. and has owned the shop for 27 years. He was given his trademark nickname “Gonzo” while serving in the USMC. He is the author of the book “Hey Look! I Found the Loose Nut”, that can be purchased online at Amazon.com or at www.gonzostoolbox.com.
Advertisement
Advertisement
Advertisement
Advertisement
Latest articles from our other sites:

Victor’s Cash Back Program Makes Select Welders and Plasma Cutters More Affordable

Victor Technologies has launched its Cash Back Rebate program for customers in the United States and Canada. Between July 1 and Dec. 31, 2014, purchasers of select Tweco and Victor Thermal Dynamics...More

‘Smart’ CTEK Battery Analyzer Ready To Work

CTEK has released its latest battery system accessory, the CTEK Battery Analyzer. All types of 12V batteries can be easily and quickly tested with high accuracy for their condition. The CTEK Battery...More

Internal Engine Oil Consumption Diagnostics

Due to the variables in engine design and ­operating conditions, internal engine oil ­consumption complaints are often the most difficult to solve. In some cases, oil consumption might be more severe...More

Hyundai Fuel System, Emissions Diagnostics

Hyundai has done a good job of improving its ­offerings over the years from both an aesthetic and mechanical viewpoint. Complemented by a strong warranty and good value, the carmaker has been able to...More

Avoid The 'Warped Rotors' Trap, Find True Pulsation Cause

The expression “warped rotors” still seems prevalent in the brake service community. According to common lore, a warped rotor is the usual cause for pedal pulsation or vibration in the car or steering...More

Getting An Accurate Toyota Tire Pressure

Ambient temperature changes can dramatically alter tire pressure, which could cause a tire pressure monitoring system (TPMS) warning light to illuminate. The TPMS must be initialized based on the tire’s...More

Victor’s Cash Back Program Makes Select Welders and Plasma Cutters More Affordable

Victor Technologies has launched its Cash Back Rebate program for customers in the United States and Canada. Between July 1 and Dec. 31, 2014, purchasers of select Tweco and Victor Thermal Dynamics...More

‘Smart’ CTEK Battery Analyzer Ready To Work

CTEK has released its latest battery system accessory, the CTEK Battery Analyzer. All types of 12V batteries can be easily and quickly tested with high accuracy for their condition. The CTEK Battery...More