Under pressure

Published: 18 May, 2017

Even apparently simple problems require thorough investigation if you want to diagnose faults right the first time

We accept a wide range of diagnostic and auto electrical work, primarily from trade customers. This means that some of the jobs we become involved with either come with no history or a nightmare history.

It is very rare to for us to see a straightforward diagnostic job. Vehicles appear with an array of replacement parts, some of these pattern parts are of such poor quality, and having been applied to the vehicle with the consideration of a cluster bomb, are often causing their own microclimate of vehicle running woes.

Healthily sceptical

This working environment means that we are healthily sceptical about everything concerning the vehicle in question. Our approach is one of initial evaluation, whilst tipping a nod to any history which may be available and focussing on the prevalent symptoms. We will then begin gathering data which may be relevant to the symptom. The data will come from a range of activities and tools such as visual inspection, road testing, the five human senses, leak detection, fuel hydrometer, pressure testing, diagnostic trouble codes, serial data stream, gas measurement, voltage and current with the meter and the scope, substitute signal and closed loop computer testing, etc.

Analysing the gathered data occurs upon the execution of each of the tests. Ideally, tests should be run only under the prevailing symptom. A list of good and bad factors is generated as the tests progress. More simple faults may give up their root cause early in the process. Some faults, particularly where poor quality parts have been used, have to be rectified in stages; we may have to undo the human causes before we can see the fault's original cause.

In curing a vehicle symptom, the data will provide the evidence as to the root cause. Sometimes the data will confirm a part or subsystem is definitely not at fault (eliminated), sometimes the data can infer that a part or subsystem may be at fault (suspected) and sometimes the data will confirm definitively that a specific part is at fault (confirmed). As the data gathering proceeds, the potential root causes are classified and the list of suspects shrinks from everything to just one thing. The skill in the job is defining the best diagnostic path to eliminate the suspects in the most efficient manner.

Lack of symptoms

A recent case which came to us with a lack of performance was a 2013 Renault Master fitted with a 2.3 dCi engine which was controlled by Bosch EDC 17 engine management system. Out of the blue the vehicle would just not rev past 3200rpm. The road-test gave an indication of fuel starvation or a lack of boost and the vehicle did not pull at all well during road test. Other clues (shown by a lack of symptoms) included that the vehicle started on the button and ran smoothly. There were no signs of exhaust smoke at idle. When the vehicle got into its upper rev range, it did produce a little blue/grey smoke though. The lack of symptoms data is as useful in diagnostics as the presence of symptoms data. For instance, if the EGR was in trouble, we would expect there to be rough idle and smoke; as these symptoms were absent, we could infer that the EGR was probably not in trouble.

An examination of the vehicle's DTCs showed the following codes, P2263 Boost Pressure Too Low (perm) and three glow plug open circuit faults (int). This vehicle had under bonnet stickers that indicated that it was fitted with a DPF and a quick visual inspection showed that there was indeed a DPF can in the exhaust and the two obligatory pressure pipes rising forth. My initial thoughts when seeing a DPF vehicle with glow plug faults and a lack of boost were to consider a blocked DPF as a potential suspect, however, a distinct lack of DPF blocked codes made me cautious about my suspicion. The vehicle did arrive from another repairer, so any codes relating to DPF issues may have been deleted previously and the van had not been driven far enough to complete a drive cycle. Sometimes knowing what we do not know can provide enlightenment and prevent distraction in the diagnostic process.

Substitute values

My next step was to take a look at the live data stream, as the symptom was ever present, the data stream would likely garner some clues as to the root cause of the issue. Choosing the parameter values carefully was probably the quickest way to build a picture of what was actually happening with the vehicle. I attempted to match the symptoms with relevant data parameters. I chose Accelerator Pedal Position, Rail Pressure, Boost Pressure, Boost Control Solenoid Command, Air Flow and DPF Pressure. A word to the wise regarding live data: There is a possibility of the engine computer using default or substitute vales in case of a problem with a component. This means that the values which appear on the scan tool may have been substituted by the engine computer.

When the engine computer calculates the fuel demand (which is then used to set the fuel quantity), it relies on several data points to look up the correct value for the operating conditions. For example, some of the values used may be engine temperature, mass air flow, boost pressure, throttle position. If one of these data values is incorrect, perhaps because the sensor has failed, the lookup value may be quite a way from what is actually required to make a good calculation, and the vehicle may run very badly or not at all. To reduce the impact of failed inputs, the engine computer uses a back-up or substitute value of data points for inputs that are out of range. This substitute behaviour is so that the engine computer can continue to run with limited inputs; the substitute values mean that although the calculation is off, it is still close enough to allow the vehicle to continue to run.

Verify

This substitution situation may mislead the unwary technician. In order that the technician gets a proper view of what is going on, the best policy is to verify scan tool data by measuring the physical output voltage from any suspect sensors. Obviously, this is more time consuming than simply observing the scan tool data, however, the payback is that the measured voltage is a true, raw, unadulterated indication of what is actually happening at the sensor. The Diagnostic Assistance software from Auto-Solve is a great tool in helping technicians understand raw sensor values to enable the performance of such tests.

Looking at the array of data, what is the weirdest parameter value? For me it was the parameter which supported the DTC: The Boost Pressure had dropped below atmospheric pressure. This indicated that either the sensor/wiring/ECU was bad, or that there was a vacuum in the intake manifold. This vehicle had a throttle valve. The symptom fitted with the data; the engine did feel as if it was being choked. But what was the cause? Could the DPF do this? No, it could cause a lack of boost, but it could not cause a vacuum in the manifold. The DPF data indicated that the DPF filter was not blocked.

Next step

So, the next step was to check out the boost pressure sensor voltage to prove its function. The sensor was easy to access and passed the voltage check, KOEO. I then used a sensor simulator to check the feedback logic of the engine computer and the sensor wiring. I sent a varying analogue voltage onto the sensor pin and assessed the live data on the scan tool and the multimeter in synch, which were shown as expected. Next up was a dynamic test. I ran the vehicle and took the revs up to the bad zone; the boost sensor voltage dipped under the KOEO value.

Root cause

Now to consider reasons for a restriction in the intake: A faulty throttle valve, blocked air intake, blocked air filter, blocked intercooler, broken/stuck compressor wheel or a collapsing intake pipe. I pulled the air filter and checked the panel filter and the air intake which were all sound and without blockages. I removed the pipe from the inlet manifold and checked the position of the throttle valve; it opened and closed as designed. I also measured the throttle valve feedback signal so that I could see the valve's position when the pipes were refitted. The turbo spun freely and was without significant play. I reassembled the pipework and then ran the vehicle at idle and measured the throttle feedback, it was open. I used a heavy foot to operate the throttle remotely so that the engine was in the "zone" and I returned to the engine bay. I looked and felt the intake pipework and I could see one of the lower intake pipes to the intercooler was collapsing (figure 1). The throttle was definitely open and the intake system was clear between the filter and the inlet manifold, a weak walled pipe had to be the cause of the problem. A relatively simple problem, the diagnosis of which was made simpler by a robust process.

Combination

Although the data provided a good clue to the root cause, the additional checks and tests provide surety in the quality of the diagnosis. It was possible to have diagnosed and replaced the pipe without any of the additional checks, but doing this would not have guaranteed a fix, as there could have been a secondary issue causing the vacuum. Using a combination of knowledge, data and a critical analytical process led to the root cause being determined, right-first-time. I was being paid to do a professional job and I could happily guarantee a fix and not a parts darts approach.

Reasoning and diagnostics Part II
We began this journey last issue, so to recap: We need solid reasoning skills to carry out effective diagnostics; persistently good decision making doesn't happen by chance. Possibly out of convenience these skills are often underestimated and undervalued by people, both in and out of the trade. We must raise awareness of the discipline and precision of thought necessary for logical and critical thinking: so we can be better rewarded for our efforts; and to make sure they are consistently and properly applied.

Reasoning, arguments and hypotheses
We covered some fundamentals in my last article: we explain our reasoning using arguments, which contain statements supporting a conclusion; one type of argument, a deductive argument, should guarantee the truth of its conclusion (if it is sound); however, we need to use critical-thinking to check this, by making sure i) there are no other possible conclusions (which makes it a valid argument) and ii) the supporting statements are true.
IAAF welcomes FIGIEFA ExVe ‘Proof of Concept’ testing
The IAAF has welcomed the news that FIGIEFA, together with other stakeholders, is conducting ‘Proof of Concept’ testing of a ‘Remote Diagnostic’ use case as part of the investigation of the Extended Vehicle (ExVe) concept.
DENSO launches new sensors for Toyota and Lexus
DENSO has added 10 camshaft and crankshaft position sensors to its range. The five new crankshaft position sensors have 129 applications across the Toyota and Lexus range incorporating both past and present vehicle models. The eight new camshaft position sensors have 119 applications across the same vehicle pool.
in-house DPF CLEANING
Recent independent market research commissioned by Kalimex and carried out by The Jamieson Consultancy found that less than half of the workshops surveyed were using on-vehicle cleaning to clear blocked DPFs. Most workshops are still removing the DPF either for cleaning on site or sending offsite.

Another interesting development is that compared to the research outcomes of the previous year, more workshops are simply replacing a blocked DPF with a new unit, when this is not always necessary.

Although offsite cleaning of DPFs is effective, the research showed that in two thirds of offsite cleans the turnaround was at least two days, rising to three days or more in a third of cleans. This means that a customer’s vehicle is off-road, taking up valuable space in a workshop. Inconvenience all round. There is a much better alternative than the current scenarios. Using a tried, tested, and effective on vehicle cleaning system, such as the JLM DPF Clean and Flush Toolkit, means a workshop can clean a blocked DPF in under two hours. This gets the vehicle back on the road fast. Happy customer and happy workshop. The costs are lower than offsite cleaning as well, with comparable results. This system is used and recommended by Darren Darling, founder of The DPF Doctor Network and his DPF Doctor members. This is about as good as it gets in terms of trade endorsement.

A workshop using the JLM DPF Cleaning Toolkit can not only offer a DPF cleaning service to their customers but can also provide this service to other workshops in the area. This comes at a time when diesel vehicles are showing a marked increase in DPF problems due to reduced running and shorter stop start journeys because of the pandemic. This results in DPFs being unable to regenerate effectively and ultimately becoming blocked with soot.

Following a successful on-vehicle clean it is important to understand the customer’s driving habits and style. Recommending a regular in tank additive such as JLM’s Emission Reduction Treatment for diesel will help the DPF to regenerate even under short journey conditions and it will prevent repeated DPF blockages. These additives could be incorporated into a workshop’s service plan to ensure a healthy DPF between regular service intervals.

More information is available at: www.jlmlubricants.com
Add more value to vehicle servicing
This article is the result of one of our trade customers, my local garage, asking for tips on how to promote some of the JLM Lubricants’ products we supply to them. Many of the products are for trade use only. For example, the DPF Cleaning Toolkit which will clean a fully blocked DPF without having to remove it. However, other JLM products are designed to prevent problems from recurring and are simple to apply. This makes them ideal for a customer to use in between having their car serviced.