Cut to the chase
Damien Coleman from Snap-on discusses how preparation can lead to easier diagnostics
Published: 28 August, 2018
Many modern systems, such as common rail diesel injection, can appear to be so complex that they seem to operate by magic. Over time, such systems are only going to become more and more complex, so understanding them means you can gain a head start on their repair.
You can be presented with a seemingly endless amount of data relating to fuel pressure feedback, fuel pressure control, cam/crank synchronisation, measured mass airflow, injector flow correction feedback, and many other areas.
However, if you prepare yourself with a fundamental understanding of the system and all data available pertaining to the fault, a systematic approach to the fault-finding procedure can be carried out.
Data overload
Figure 1 shows the live data returned from a common rail diesel injection vehicle with an EDC16 engine management system.
There is an enormous amount of data available from these data parameters, which can allow you to ascertain the nature of the fault. The actual operation of the fuel system can be compared to the desired system operation and using the data, a decision can be made on the condition of the system and where a fault (if any) may be.
An oscilloscope is another important tool when investigating a fault with such a complex system. Figure 2 shows an oscilloscope waveform from an Audi with the 2.0L common rail engine. The yellow trace is the fuel rail pressure sensor voltage (feedback) and the green trace is the current flow through the inlet metering valve (command). The waveform was captured during a wide open throttle (WOT) condition.
This image alone tells us that the fuel inlet metering valve is a normally open valve. The engine control module (ECM) decreases the duty cycle when the required fuel pressure is increased. This allows less current to flow through the solenoid and the valve is allowed to open, which increases the fuel pressure measured at the fuel rail.
Full analysis
When the fuel pressure demand decreases, the duty cycle control from the ECM increases. This allows more current to flow through the solenoid which results in a reduction of the fuel pressure. Duty cycle is often referred to as pulse width modulation (PWM) control.
The duty cycle control on the ground side of the fuel inlet metering valve can be analysed using an oscilloscope, as seen in Figure 3. The waveform below displays the fuel rail pressure feedback voltage (yellow trace) and the fuel inlet metering valve duty cycle control from the ECM (green trace).
The oscilloscope is connected to the control wire for the fuel inlet metering valve. The technician must be mindful that this is the ground control circuit. System voltage on this wire indicates open circuit voltage. The diagram in Figure 4 shows the best method of connecting this set-up.
By careful analysis using serial (scan-tool) and parallel (oscilloscope) diagnostics you will now be in a position to identify the area of concern accurately and in a timely manner. Knowledge, together with the right equipment and experience therefore benefits technicians by leading to a reduced diagnostic time and an easier fault finding method, rendering these complex systems much less so.
TT Archives: Top Technician issue ten 2016 | www.toptechnician.co.uk
- Ben shines spotlight on workplace bullying
Ben has launched new web resources to help people cope with bullying in the workplace, just in time for National Anti-Bullying Week, which is taking place this week (12-16 November).
- Customer care in the garage business
Customer care is vital to the survival of most companies. Without customers we do not exist. This is extremely important in the independent repair sector as we are the
service providers.
In the face of ever-growing competition, it is very important for us to portray the image of a professional efficient business that cares about its customers. If you deal with customers and you represent your garage, it is vital that you look after all of your customers, all of the time.
Positive relationships
Without positive relationships with our customers no business can survive in today’s competitive marketplace. Just consider the number of customers you have had up until now, imagine what things would be like if they all disappeared overnight!
Customer care has changed immensely over the years. Customers have become less tolerant and more demanding. It is a huge challenge for us to meet these demands. However, the answers are within us all.
We all know that customers who are happy with the service we provide are more likely to purchase again and recommend us to others. You may even know that customers that are very impressed with our service rather than just satisfied are willing to pay higher prices for our service. You will certainly have awareness of the fact that when you treat customers in the correct way and display a positive and pleasant attitude, you will usually receive the same back from them.
The best form of advertising
Businesses that have developed an excellent level of customer service will usually find themselves in a situation where customers become advocates for their business. In many cases this becomes their best form of advertising. The alternative is a situation where customers feel they must let people know of their negative experience and are quick to do it. The implications of this can be extremely damaging and many businesses struggle to overcome the negative label.
The basics of customer service are actually very simple. We know that being polite, smiling and making the customer feel good about themselves and their service/repair purchase is at the core of creating a good customer experience. However, tthese days that is no longer enough. Customers have become much more discerning, they have a much greater awareness of what is going on in the world, what they should expect from a garage and that it is very simple for them to take their business elsewhere when their high standards are not being met.
Customer care breakdown
Customer care includes the following elements:
- Skills, bills and jaw-aches
I knew starting a business would never prove easy but we don’t get anywhere in life without taking a risk or two. Having been in the industry for a few years now I have learnt that the two main attributes a successful car repair workshop needs is the skill to diagnose and repair and the ability to communicate with their customers.
Modern car repair facilities have seen a dramatic change in recent years with the huge advancements in computer-related faults. The main tool of repair has seen the demise of the hammer and the growth of the diagnostics fault reader. I am a hands-on mechanic and much prefer older vehicles where I don’t need to locate the OBD port before the bonnet release, but I have to move with the times if I am to succeed as a business and that is why I am looking at hybrid servicing and trying to tap into that market. It is tough for me to admit that as I love working on classics and I will still have a part of the workshop for the golden oldies but it is hard to ignore the impact hybrid and electric vehicles are starting to have on the repair market.
Communication
The car repair industry has a pretty bad reputation – lets be honest. My female friends and family dread having to buy a car or go to a garage. Communication for me is so important, as with any business it is crucial that you are able to talk to customers and listen to their concerns without belittling them. The issue with car repairs is that it is a complicated process that is difficult to explain in layman’s terms and which can alienate an individual if they don’t understand. There is also the problem of distrust. If a customer doesn’t understand the problem and how you are able to fix it you risk confusion and doubt. There are so many horror stories of people being fleeced and conned as they don’t understand how a car works that every customer feels like you are going to do the same, it takes a long time to earn a good reputation and just one bad experience to send your business crashing down.
I always like to explain as simply as possible with the work I am doing, I keep the broken part so that I can show the customer what I have replaced and what their hard earned cash has been spent on, I also take pictures and probably over explain everything. It is important for my business that I gain a good reputation as word of mouth is my main advertisement. As busy as a car workshop is always make time to have a friendly chat with your customers, especially if they have a trade, you never know when you might need a plumber!
So, this month has been busy, productive, stressful and hot (I am writing this in July) but the world of car repair stands still for no-one.
- Non-intrusive testing
As technicians we’re all expected to be able to diagnose a fault within a sensible timescale, for a reasonable price, then guarantee the fix. With correct training, information and tools this is possible. However, we are often faced with multiple faults where cause and effect may not always be straightforward. We can be in a situation where we need to rectify faults before we can move on to the next. Also, if the repair cost could outweigh the vehicle’s value or customer budget then great care must be taken explaining the situation, agreeing a starting fee and preparing and executing a successful diagnostic plan.
Recently we were presented with a BMW X3 for poor performance and a suspected DPF fault. After interrogating the customer we gathered all necessary information. Initial diagnosis confirmed multiple fault codes and a blocked DPF. Determining what caused the DPF to block is vital for the correct diagnosis and preventing reoccurrence. We created a test plan to test each fault and separated them into faults that affect the performance, faults that can cause the DPF to block or prevent regeneration and ones that don’t. In order to fully test the vehicle we would need to clean the DPF first as the exhaust back pressure was so high, the vehicle was barely drivable. As a member of the DPF Doctor network we have a very successful method of cleaning the soot from the DPF without the need for removal and access to many manufacturer-specific tips with DPF faults. The information and knowledge within the DPF Doctor network has proved to be invaluable and has given us an outstanding success rate. With our test plan ready we were able to calculate a sensible labour figure to conduct the tests required. The customer authorised the labour and the DPF clean.
Several faults were straightforward. A multimeter gave us conclusive results and made it easy to quote for replacement parts and labour time to fit them. The main fault causing poor performance required a little more thought to keep diagnosis time to a minimum. A low boost pressure fault code doesn’t tell us why the pressure is low. Driving the vehicle whilst monitoring the boost pressure showed the fault was intermittent, so an external boost leak was unlikely. A smoke test was also carried out which revealed no leaks. In this instance, the EGR valve could be a likely culprit. This engine uses a vacuum controlled EGR valve with a position sensor built into the diaphragm. As tempting as it was to unbolt it and take a look, this would all take more time then factor in the risk of rusted bolts etc. With a position sensor one would think if the valve was to stick then a fault code would be set. We had to plan a simple, conclusive, yet non-intrusive way of testing the EGR system quickly.
The conventional vacuum controlled EGR system consists of the EGR valve which includes the diaphragm with a 5 Volt position sensor and the vacuum control solenoid valve which uses vacuum from the brake servo vacuum pump and is controlled by the ECU on a duty cycle. The position sensor will typically show 0.5 to 1.2 Volts when fully closed and 3.9 to 4.5 Volts when fully open. One side of the solenoid valve has a 12 Volt (battery Voltage) supply and the ECU switches the ground path on and off at varying duties to vary the vacuum amount thus varying the EGR valve position. The ECU looks at the position of the valve and adjusts the duty to achieve the position desired similar to how an ECU uses the oxygen sensor to adjust the air/fuel ratio. With the following tests we were able to check every component in the system.
Test one
We connected the Mityvac directly to the EGR valve and the oscilloscope connected between the signal wire and battery ground. As we had already smoke tested the entire inlet system we connected the smoke machine directly to the inlet manifold in place of the intercooler hose. With the smoke machine running and the ignition on (engine off) we used the Mityvac to fully the valve to check it had no vacuum leaks (split diaphragm), then we opened and closed the valve slowly and then quickly. This confirmed the following:
- Garage sector motors ahead in survey
An annual survey of 1,000 car owners conducted by The Motor Ombudsman has revealed that consumers have an increasingly favourable perception of the vehicle service and repair sector when compared to the same period last year. The study showed that 51% of respondents enjoyed a positive experience, versus 44% in 2017, whilst 39% of individuals expressed a neutral view in 2018 compared to 45% 12 months earlier.
