Category Archives: Engine Management

General drive systems maintenance

In 1990, Gates introduced the PowerGrip timing belt kit for Synchronous Belt Drive Systems (SBDS) to the market. At that time, only 6% of installations were timing belt kits. Since then, drive belt technology has been enhanced and timing belt tensions have increased as improvements in the belt materials have allowed replacement intervals to be extended. Today, 90% of installations are belt kits and it is accepted that changing the metal parts at the same time as the timing belt is good preventive maintenance practice – except when it comes to the water pump.

Drive development
High performance engines increasingly depend upon the reliability of drive systems that are designed to run for between 80 and 100,000 miles or more. The routing of the belt and the drive system layouts often differ between models in even the same range. What’s more, OE manufacturers make adjustments to replacement components for existing drive systems or update their recommendations about component installation. Sometimes, this may demand a completely different approach to the installation of the belt or tensioner.

Until recently, water pumps were ignored when it came to regular checks and replacement procedures. However, the water pump bearing is likely to have done just as much work as all the other bearings in the drive system.

Checking water pump bearing in the SBDS

Water pump change
By their nature, drive systems are hostile environments. Premature failure is often caused by dirt thrown up from the road or water ingress, so a leak from the water pump could prove catastrophic to the SBDS. Over the long-term, it makes sense to change the water pump at the same time as the belt because:

1) Prevention is always a better policy than rectification;
2) To replace the water pump, the timing belt has to come off anyway;
3) A used belt cannot be re-fitted;
4) The water pump is subject to wear.

A complete preventive maintenance approach can guarantee customer satisfaction for years to come and there are other advantages. For example, Gates supplies a water pump kit, complete with pump, belt and all the metal parts required to perform an SBDS drive system overhaul. Sourcing the belt kit and the water pump from the same supplier in this way is a smart move. In the event of a problem, technical support is just one phone call or inspection away.

We recommend that kits should always be installed, rather than just belts. Changing the water pump as part of the belt kit makes economic sense both for the customer and the garage. It may save the cost of re-visiting the drive system to replace the water pump in a few months time.

Accessory Belt Drive Systems (ABDS)
ABDS drives are so much more sophisticated, these days. If it is becoming accepted that a drive system overhaul is the route to complete SBDS maintenance, the same argument applies to the ABDS where the number of components has increased.

For example, Torsional Vibration Dampers (TVD) and Overrunning Alternator Pulleys (OAP) are becoming integral parts of the drive system, but the function of OAPs and TVDs is not always fully understood.

TVDs have been designed to take out vibrations produced by other associated parts. Unfortunately as they themselves begin to wear, problems occur elsewhere in the drive that may be incorrectly attributed to the belt or tensioner. Belt replacement alone will not resolve the issue.

More parts in the ABDS means more checks for wear

Technical workshop programme
Increased product knowledge and regular inspections of each drive system – as part of a preventive maintenance policy – is vital. Gates has been working with motor factors and garages to help installers appreciate the benefits of preventive drive system maintenance, understand the pace of technological developments and avoid common installation errors. They also help to explode many myths relating to drive system maintenance at the same time.

These cover:

  • Available technical support
  • Increasing workshop efficiency
  • Reducing fitting times
  • Installation issues, diagnostic techniques and solutions.

The technical workshop programme for 2012, developed in association with local motor factors, is currently being drawn up. Speak to your local Gates distributor to find out if one is taking place near you.

EGR cleaning – a comprehensive guide

The first thing that you need to understand is that this tool is not just for cleaning the EGR valve, but the whole EGR system instead.

The principle behind Exhaust Gas Recirculation (EGR) is to introduce measured amounts of exhaust gas into the combustion chamber to reduce the amount of Nitrous Oxide (NOX) in the emissions of the engine. This is achieved by introducing exhaust gas into the inlet manifold via the EGR system.

On a modern turbo diesel engine the recirculation of exhaust gas is not just controlled by the EGR valve. Exhaust Gas Recirculation (EGR) is a process that relies on the correct function of the turbocharger, EGR cooler (an inline heat exchanger that reduces the temperature of the exhaust gasses), the EGR valve and the inlet manifold and associated components.

The negative impact this process has on the EGR system is that exhaust gasses have a high carbon content, which clogs and restricts the function of the EGR system.

The TerraClean EGR tool is designed, not to clinically clean, but to restore flow and function back to the EGR system by removing the excess carbon deposits within the system. It can be used to cure various faults including: sticking EGR valves, clogged EGR coolers, sticking variable wastegates on VNT turbos, restoring air flow to inlet manifolds, improving swirl flap operation and cleaning DPFs.

The EGR cleaning tool process in 5 easy steps

STEP 1

Firstly the technician has to gain access to the internal components and surfaces of the system.

This is achieved in a variety of ways, depending on the engine. On a newer Euro V engine, access is gained by removing the EGR temperature sensor, which is normally located within the EGR cooler. An adapter is positioned in place of the temperature sensor, allowing the TerraClean EGR cleaning fluid to be introduced here.

On an older engine, access is a bit more intrusive, usually entailing the removal of a pipe that connects the exhaust manifold to the EGR valve. In extreme cases, it may be necessary to drill and tap a hole into the exhaust manifold, which is capped off after the process is complete.

STEP 2

Always starting with a cold engine, the technician connects the tool in a specific way so that they can force the fluid through the exhaust manifold, turbo and exhaust. This is achieved by isolating or disabling the EGR valve, thereby leaving it closed or disconnected.

The technician starts the engine and, at idle, begins to introduce the specifically formulated fluid – TerraDiesel EGR and Induction System Cleaner – in 250ml increments into the system.

The technician leaves the engine running throughout so that just compressed air is passed through the manifold for about five minutes – this keeps the temperature in the manifold to a workable level. On first application to a vehicle, an amount of fluid between 750ml and 1litre should be run through the exhaust.

STEP 3

Next, the technician begins to introduce the fluid through the EGR cooler and valve; this is achieved by actuating the EGR valve into the fully open position.

This procedure can only begin after the engine has been started and is running at a fast idle. Again the fluid is introduced in 250ml increments with just compressed air running in-between. This stops the fluid from welling up inside the inlet manifold, eliminating the risk of hydraulic lock of the engine.

The technician would normally run about 500ml of fluid though the valve itself with the aim of removing the carbon deposits from the valve seat, allowing it to seal properly again.

STEP 4

The next step is to restore flow to the inlet manifold, which is achieved by spraying the fluid directly into the inlet manifold while the engine is running. The process removes excess carbon from the walls of the inlet manifold and the inlet ports, thus allowing air to move more freely through the manifold.

Again the amount of fluid used would be approximately 250ml increments at fast idle and running just compressed air in-between to eliminate the risk of welling and hydro locking the engine. Depending on how badly the manifold is contaminated, this determines the amount of fluid used (usually between 750ml and 1litre).

STEP 5

Following completion of the final process, the vehicle must be driven for at least 10 minutes with at least three aggressive accelerations within the first couple of minutes. This expels any fluid which may have welled in the DPF.

BEFORE

AFTER

How do Stop-Start systems work?

The last few years have seen the introduction of Stop-Start systems by many manufacturers across various vehicle models to improve fuel consumption and reduce exhaust emissions.

One of the main problems the introduction of Stop-Start systems has caused is that when the starter is operated the voltage in the vehicle’s electrical system can drop. In normal circumstances this is not a problem, the vehicle is not usually in “driving mode” and it doesn’t matter if some of the vehicle electrical systems do not function during starter motor operation (exterior lights, heating & air conditioning and audio systems, for example). However, during driving this is not acceptable for reasons of safety and driver convenience.

To counter this problem most systems use an additional power supply to ensure that voltage-critical equipment will not stop operating during starter motor operation. For some models this consists of a large capacitor that is charged by the alternator using engine power, or kinetic energy generated during deceleration and braking.

Considerable thought has been given to the safety mechanisms; most, if not all, Stop-Start systems will not operate if any of the doors or the bonnet is open and will only operate if sufficient vacuum is available to ensure the normal operation of the braking system.
As the use of Stop-Start technology is increasingly adopted, there are now as many systems as there are manufacturers, but they can be categorised as follows:

  • Those using a “conventional” starter motor
  • Those using a combined starter motor/alternator

Although some models use a conventional starter motor for cold start and Stop-Start operation, it is usually modified to ensure it can withstand the extra use it will encounter. However, the time taken to start the engine with this system is thought by some to be too long so other models are using a different approach.
Battery technology is also changing, with the extra starting cycles requiring a more robust battery construction. Absorbent glass matt (AGM) batteries, Gel batteries or the slightly cheaper enhanced flooded batteries (EFB) variants can be found in most vehicles with Stop-Start systems. Replacement of these batteries may necessitate programming of the vehicle’s computer system to allow the battery degradation process to be monitored. On many models the Stop-Start system will be disabled for up to 24 hours following battery disconnection or replacement to allow the battery condition to be evaluated.

Which Stop-Start Application Do They Use?
Toyota Yaris

The Stop-Start system of the Toyota Yaris has its starter motor in constant engagement with the flywheel ring gear and then the ring gear is connected to the engine flywheel with a one way clutch. This, together with recognition of the engine’s static crankshaft position, allows instantaneous ignition of the correct cylinder, thereby reducing starting time.

It is interesting to note that the number of starter motor operations is recorded and the calculated “end of starter lifespan” is indicated by a flashing warning lamp on the instrument panel. After replacement of the starter motor the counter has to be reset.

PSA group

Using a conventional type of starter motor for cold start, the Peugeot/Citroen group employs a combined starter motor and alternator assembly (so called reversible alternator) for the Stop-Start system. Connected to the engine crankshaft with the auxiliary drive belt, it provides silent operation and short starting time.

Unlike conventional alternators, diodes are not used; instead voltage rectification and motor operation use metal–oxide–semiconductor field-effect transistors (MOSFETs). Presently, it would appear that it is only the “e-HDi” models that use the aforementioned capacitor.

3 Essential Items That You’ll Need When Servicing Stop-Start Systems

Starters & Alternators 

Used in many modern vehicles, StARS (Stop start Alternator Reversible System) consists of a reversible alternator that replaces the conventional alternator and starter motor. The reversible alternator provides the function of alternator and starter combined with the new design allowing the conversion of electrical energy into mechanical energy, and visa-versa.

StARS works similar to the conventional alternator where the later applications would have the charge rate controlled by the vehicle ECU (computer controlled and smart charge systems). The new variation now has a separate ECU which administers the reversible alternator and the vehicle’s engine.
When the vehicle is slowed down by the user the ECU analyses the speed of the car and if/when the speed falls under 5mph the ECU switches off the engine. Once the brake pedal is released the ECU then gives an order to start the engine again. The reversible alternator plays the part of the starter motor to achieve this.

The system is designed to work in 5 phases:
1. The vehicle is switched on and the ECU will crank/start the engine. This is achieved by the battery providing electrical energy and the reversible alternator then acts as a starter motor to help crank the engine.

2. During normal driving (when the vehicle is not being slowed down) the reversible alternator then acts as a conventional alternator by converting the mechanical energy into electrical energy and charging the battery.

3. Once the vehicle speed has been reduced below 5mph by braking the StARS ECU gives a command to stop the engine.

4. Once the brake pedal has been released the StARS ECU then gives a command to start the engine again. The battery provides electrical energy and the reversible alternator plays the part of the starter motor and cranks the engine.

5. The vehicle is switched off and the ECU will stop the engine

AUTOELECTRO provides a whole array of replacement starter motors and alternators for modern Stop-Start systems and applications.

Servicing Data 

AUTODATA has enhanced its online product offering to include technical information on vehicles with Stop-Start technology.
The technical information provided by Autodata on its online system enables technicians to identify the specific location of key elements such as the main battery, additional battery and the Stop-Start capacitor.

Procedures for disconnecting and reconnecting each element are clearly explained along with additional information for servicing the system.

Replacement Batteries
EXIDE has expanded its coverage of the UK car parc with new AGM and ECM batteries. The new products cover vehicles from VW, Audi, Toyota, Ford and a slew of other brands.
Exide’s AGM batteries are claimed to have around three times the lifecycle durability of standard batteries. Parts of “matching quality”, they are designed for cars with Start-Stop and regenerative braking systems. They are also used in standard vehicles to increase endurance and performance.

AGM battery coverage: Audi A1, A4, A5 and Q5; BMW 5, 6, 7, X5 and X6; VW Golf, Polo and Touareg; Chrysler Voyager; Dodge Caliber; Jeep Cherokee and many others.

ECM battery coverage: Ford Fiesta, Galaxy, Focus, Mondeo, B-Max, C-Max and S-Max; Toyota iQ; Mazda CX-5 and a range of other models.

How to test Air Mass Meters while they’re still on the vehicle

Believe it or not, potentially faulty Air Mass Meters can be checked whilst the component is still fitted to the vehicle. Although it may not be possible to conduct the same extensive testing that AMMs undergo in a dedicated test facility, such as Lucas’s, faulty sensors can still be diagnosed in the garage environment without removing the part from the vehicle. Here’s how:

Testing a traditional AMM using a voltmeter

Many AMMs can be tested on the car using a voltmeter. Typically, AMMs have an analogue output ranging from a possible 0V up to 5V; however, a 5V signal would usually be a saturation point, so you wouldn’t normally see a reading this high.

Bosch-type AMMs generally have a minimum voltage of around 1V; therefore, by using a voltmeter to probe into the sensor wiring at ignition on, the voltmeter should show this value.

TOP TIP: It is always advised to take a ground connection from the battery negative. You then only have to find the output pin on the sensor, which is normally on the end.

Starting the engine will raise the voltage to the level for idle air flow. Then, with some gradual acceleration, you should see the voltage rise in conjunction with the rev count of the engine. The reading will then drop back down as the engine slows back to idle.

A healthy AMM should show a smooth voltage change with no jumps or hesitation. A constant voltage that doesn’t change with acceleration indicates that the AMM is faulty and failure can often be caused by contamination from oil or debris.

TOP TIP: All sensors have a 12V feed, with some having one or two additional 5V inputs. It is worth noting that Siemens-type sensors will sit at a lower ignition voltage than the Bosch – commonly around 0.6V.

Testing a digital AMM using an oscilloscope

Newer digital-type AMMs are not easily checked with a voltmeter and will require the use of an oscilloscope in order to perform a test on the vehicle. Digital sensors have become more commonplace due to their faster reaction times and improved accuracy.

TOP TIP: Digital sensors are often moulded into the measuring tube rather than screwed. The output of digital sensors is viewed with an oscilloscope as a digital waveform. Rather than an increase/decrease of voltage in proportion to airflow, it is the change in frequency of a waveform that is analysed.

Below is an example of the signal at ignition on (Fig 1) and another with air passing through it (Fig 2). The wave gets closer together as the air flow increases on this sensor (i.e. the frequency increases).

Fig 1

Fig 2

Whilst digital sensors are not as easy to check as the analogue type, it is still possible if you have the correct equipment. As newer vehicles generally have this type of sensor fitted, it is a worthwhile investment.

Why the combustion process in some spark ignition engines is anything but normal

In order to establish ‘abnormal’ combustion, we need to first consider ‘normal’ combustion. Irrespective of engine type (gasoline or diesel), normal combustion is where the combustion event that creates the energy release happens predictably, at the correct time relative to the piston position, in order to produce the maximum amount of mechanical power from the chemical energy in the fuel. In some circumstances or operating conditions, this does not happen effectively and this reduces efficiency, wasting fuel and creating excessive emissions (either of harmful gases or noise). In extreme cases engine damage can also occur.

Knock is often given alternative names. ‘Detonation’, ‘Pinking’ and ‘Pre-ignition’ are just some of the terms used to describe it.

Let’s look in more detail at abnormal combustion for gasoline engines, considering the impact of abnormal combustion on engine operation.

Gasoline engine – Knock Spark knock

The phenomena of knocking combustion in spark ignition engines is caused by the spontaneous, self-ignition of the fuel-air mixture in the combustion chamber, before it is actually reached by the flame front developed by the normal combustion event. The rise in pressure, in front of the flame, leads to a temperature rise in the unburned gases. In extreme cases, the thermal increase in the end gas leads to a situation where the required heat energy for combustion exists, and thus uncontrolled self-ignition takes place.

Depending on the mass of the end gas contributing to the self-ignition, a very rapid pressure rise takes place, leading to high-frequency acoustic oscillations that generate the characteristic ‘knock’ noise. Although this noise can be quite subtle, the damage that can be caused by the high pressure, high frequency pressure waves is quite considerable. Erosion of pistons and gaskets is expected, and if knock is sustained, surface temperatures of the engine components increases beyond design limits, causing further damage.

Piston land area damaged by knock (source: AVL)

During a normal combustion event in a gasoline engine, the flame front, initiated by the spark, progresses through the fuel/air mixture at approximately 10 to 50 m/sec. The pressure in the combustion chamber is more or less uniform (that is, the same at all positions). When knocking occurs, the high frequency oscillations create reverberating pressure waves that travel across the combustion chamber at high speed, generally, at the speed of sound for that temperature and pressure condition.

Pre-ignition

End-gas self-ignition – also known as ‘spark knock’ – will generally respond to changes in ignition timing and/or fuel quality and is therefore controllable to some extent. It is a challenge for the engine and combustion system designer to be able to increase the efficiency of the engine via higher compression ratios, but spark knock is a limiting factor!

Improved combustion chamber design, with adequate cooling, in conjunction with advanced knock control systems, helps to achieve the optimum combustion concept. Another knock phenomenon is true pre-ignition; something else igniting the fuel/air mixture prior to the timed spark. This causes incorrect timing of the energy release in the cylinder and considerable engine damage that can occur in a very short space of time (a few engine cycles). This type of uncontrolled ignition, which causes extreme knock, is becoming a concern to modern passenger engine manufacturers.

Highly turbocharged, downsized engines operate close to their design limits – they are highly stressed mechanically and thermally. This pre-ignition, caused by hot surfaces, produces high intensity knock, known as ‘mega’ or ‘super’ knock. This must be avoided at all costs during engine operation as damage will very often occur. The cause of this type of knock is thought to be the effect of deposits building up on valve tulips – breaking free and being induced into the combustion chamber, subsequently being heated and causing self-ignition during the compression stroke.

Most modern engines now use a combustion chamber mounted direct injector and it is thought that, due to the lack of fuel washing over the valve tulip from the direct spray of a port mounted injector, this allows the build-up of deposits to occur. It should be noted that knock is still not completely understood as it is a complex phenomenon; in addition, there is always some disagreement in academic or research communities. The subject itself can be quite subjective!

It is important to note that for a gasoline engine, engine knock is the limiting factor for the production of torque and power at any given engine operating condition (speed and load). Generally, for a given condition, the ignition timing is optimised to the position that gives best torque, just prior to the onset of knock. Finding this point is part of the engine ECU calibration process and thus, being able to detect and measure knock is important in engine research in order to be able to develop and calibrate the engine control system to run as close to the knock limit as possible, without causing engine damage.

Spark advance curve showing the position of MBT (Minimum spark advance for best torque)

Knock sensing and measuring
Knock sensors are very often encountered on modern engine control systems. These are basically vibration sensors, tuned to the specific knock frequency of that engine (in a similar way that a tuning fork resonates at a specific frequency). When knock occurs in the cylinder, the vibrations travel through the engine structure and excite the sensing element in the knock sensor (normally a piezo-electric element). This produces a characteristic ringing voltage that the ECU can detect, and then respond to accordingly.

A cylinder pressure curve showing a ‘knock’ signature

There is an important point to note when installing or replacing knock sensors on the engine – you must use the correct installation torque with a calibrated torque wrench. Why? When installing and applying torque to the body of the sensor, stresses are introduced into the sensor housing. If the incorrect torque is used, the stress value and stress distribution will be affected and the natural frequency response of the sensor will be altered. That means it will be sensitive at the wrong frequency and may not work at all!

Typical knock sensors for structure borne vibration detection – used for knock detection in gasoline engines (source: Bosch)

Measuring and evaluating knock is a science in itself. Researchers are constantly looking for more sophisticated methods for examining and understanding the phenomena, and predicting its onset. This information is then used to optimise the combustion system to reduce sensitivity to knock. Then, to calibrate the control system that will have to prevent knock, right throughout the life of the vehicle under a multitude of operating conditions.

An instrumented spark plug for combustion visualisation and knock prediction (source: AVL)

The latest measurement technology for engine research uses optical fibres to build up a visual pattern of the combustion event. This can then be used to monitor the progress of the flame front from the initial ignition event, right throughout the combustion process to the end gas combustion. This can be installed via instrumented spark plugs that include optical fibre bundles.

Image created via optical instrumented spark plug, showing the flame intensity. It highlights the hot spots with major knock probability (source: AVL)

Summary
Knock is a complex subject that divides the experts in their opinion. However, it is a crucially important topic for the development of new engines, and is therefore of great interest.

KNOCK, KNOCK!

  • Knock is a phenomenon of spark ignited engines. It is caused by spontaneous, self-ignition of the end gases during normal combustion.
  • It causes damaging, high frequency pressure waves that can destroy the engine components in the combustion chamber.
  • The octane rating of the fuel determines the limit of ignition advance for a given engine speed and load condition, The higher the octane rating, the slower and more controlled the fuel burns and hence, the greater the resistance to auto-ignition ‘knock’.

Why does poor turbo boost occur?

Unfortunately, simply installing a direct replacement may not be the end of the story when a workshop is faced with a problematic turbocharger.

If performance problems in a petrol-engine vehicle persist, even after the replacement has been fitted, the issue may well be due to a malfunctioning recirculation air valve (RAV).

If the RAV is damaged or malfunctioning, the inevitable result is poor engine responsiveness and, to make matters worse, the problem could even lead to the turbocharger failing as a result of it being overloaded.

The RAV is installed either directly on the turbocharger itself or in the pressure side area of the charge air line. Poor engine performance can be caused by factors such as a ruptured membrane on the inside, leaking control lines or corroded plug contacts.

With electronic RAVs, an entry is generally created in the ECU, so checking the fault memory will save workshops a lot of time and unnecessary labour.

What does a RAV do?
The task of the RAV is to take a proactive measure against turbo lag by preventing a backlog of charge air, which can accumulate as a result of gearshifts and causes the deceleration of the rotating assembly.

If the driver suddenly eases off the accelerator pedal at high turbocharger speed, it will cause the throttle valve to close and high dynamic pressure to be generated on the compressor side, which cannot escape. This counter pressure drastically slows down the impeller and leads to high mechanical loads on the turbocharger and the closed throttle valve. Once the gear change is completed and the throttle valve reopens, the turbocharger has to be brought up to speed again, which is why there is a delay.

RAVs minimise the delay following these load changes – commonly known as turbo lag – by releasing the accumulated charge air between the compressor side and the closed throttle valve via a bypass. Once it has passed through the compressor, it is guided back into the intake section ahead of the turbocharger.

This loss of pressure on the compressor side prevents a deceleration of the impeller and when the throttle valve reopens, the RAV closes and the boost pressure increases immediately. Therefore a noticeable drop in performance should always lead technicians to check the RAV before replacing the turbocharger.

Turbo range
Through its joint venture with Bosch, MAHLE Aftermarket is now able to supply the UK aftermarket with an extensive range of OE quality turbochargers for petrol engines developing 45-220 kW and diesel engines rated between 35-165kW.

Latest additions to the MAHLE Original range are part numbers 011TC17498000 for four cylinder 92kW engines fitted to Vauxhall Vectra, Saab 9-3 and various Volvo models, 082TC14411000 for four cylinder 135kW engines used in BMW 3 Series and X5 models and 222TC15242000 for three cylinder engines fitted to the Smart range.