Non-intrusive diagnostic techniques
Frank Massey examines various ways for you to get the answers you are looking for when working on a vehicle
By Frank Massey |
Published: 04 September, 2020
The last two topics in recent issues focused on combustion issues and the various tools, service and repair process available to us. Two reasons have directed me to develop this debate further, firstly an email from my much-respected friend Phil Ellison at ASNU, and a VW Golf edition 30 presented to our workshop with poor running at low and transient throttle position. I was also involved in a conversation with friends in Perth, Australia over valve timing issues.
I’m going to respond to Phil’s interesting input first and clarify something especially important to all diagnostic techs. All decisions we make must be evidence based and not opinion. This is an extremely broad statement, but simplifies the fact that if you do not have access to the required tools, software, or process skillsets your decisions will be opinion-based!
I can relate this to my time building military aircraft, where nothing ever happens as a result of opinion. You could quite literally switch off and simply follow the build schedule and submit your work to inspection. You were not paid to have an opinion. This is why I left!
I may have previously left an impression that it was not necessary to fully evaluate injectors in a test bench, if this was so, then I apologise as my thoughts are the exact opposite. My intention was to ensure that you fully explored all causes of incomplete combustion while the engine is running, as most engine work now carries a high labour content! Do not, however make the mistake of letting cost dictate your process. Phil did pick up on the common issues of injector removal damage where specialist tools are required. The use of fuel additives, which can be a common cause of internal injector damage especially to plastic filter baskets, where any debris is then deposited in the basket effecting fuel flow. Direct injection technology now demands the absolute best fuel quality, often reinforced by manufacturers placing fuelling advice inside the filler flap.
Phil also picked up on a common issue I did omit; Stop/Start. Hot engines with an increase in stop events, with fuel trapped in the injector often causes lacquering of the pintle. Heat in the combustion chamber dries any combustion residue and oil on the injector tip. I’m coming to the inlet valves very shortly…
Fuel trim or correction does not fix problems, it can exacerbate them, imbalance in injector delivery or as Phil pointed out deterioration of the spray pattern will cause bore wash, premature lubrication failure, and an increase in crankcase emissions, larger fuel droplets do not combust fully.
Interestingly, he pointed out that new injectors are produced with a +/- 5% tolerance.
Potentially misleading evidence
The Golf appeared in our workshop just a few days after I had finished my topic. I was not involved in most of the diagnostic process or repair but was in discussion over potentially misleading evidence.
The vehicle had covered 106,000 miles, and was suffering from poor idle and incomplete combustion, with a mil light indication.
Step 1/ serial interrogation
0568/P0238 boost sensor, signal high, frequency 1
0768/p0300 random/ multiple cyl misfire, frequency2, counter re-set 255
0772/p0304 cyl #4 misfire intermittent frequency2 counter re-set 255
The next step taken was a cranking current differential test, showing no apparent mechanical imbalance? Back to this later.
Coil and plug failure is a common problem and is an obvious job for the Pico scope, no problems with burn times or primary current saturation here.
David Gore, our diagnostic tech, opted for the first look sensor in the exhaust next. I’m not sure if he opted for WPS in cylinder or not. This would have been my preferred choice, but as the saying goes too many chefs…
If you refer to Fig.1, The image is triggered from ignition, sequentially 1342 from left to right. I’m going to let you debate this image, as I intend to cover this in detail next month. I bow to Brendon Stickler’s wisdom on exhaust pressure evaluation. My debate is focused on the properties of pneumatic pulse delay from the cylinder head to tail pipe. I have since proven this and will discuss this in the October issue.
The next and obvious decision was to remove the manifold and check the intake tract and valves for carbon.
So, as you can see in Fig.2, there is excessive intake valve carbon. This is due to several factors, the most common of which is no self-cleaning from the fresh fuel air intake cycle. Other factors include, lengthy oil service intervals, not replacing oil separation filters, poor fuel quality, driving environment, poor or incomplete combustion cycles, incorrect atomisation and air swirl during the intake and combustion preparation cycles. Remember, direct injection can separate the fuelling into several events on both the intake and compression strokes.
Value
Back to a comment I left open earlier, I hope you are still interested? The value of compression is determined by the mechanical engine efficiency and volumetric efficiency, Pumping losses! So why didn’t a problem show up during the cranking balance check? As this test is based on compressional resistance. Accepting that when the engine was at idle it ran badly and would eventually disengage the injector cycle in cly #4? the answer is rotation speed increase reduces the available time to draw in fresh air. If you compare nominal compression values say 10-12bar against the value at idle they will only be around 3.5 bar!
The detrimental effects of intake fouling only tends to occur at closed and partially open throttle, where the pumping losses are the greatest. The dtc relating to boost pressure sensor value high, can be caused by ignition misfire or unstable intake pulses.
Finally, the injectors were subject to the Spanish Inquisition in the ASNU bench. The results (see Fig.3) confirm substantial fuelling imbalance causally relating to my previous comments.
My grateful thanks to Phil, David (and myself), for the technical input in this topic. I’m off to the workshop to check the delay characteristics with WPS in cylinder and FIRST LOOK sensor in the exhaust.
- A month in the life of a vehicle technician
The last topic concluded with a promise to share my experiences working within a workshop lacking in essential infrastructure. I hope by explaining my failings and limited success, it helps identify the importance of correct process, correct tools and comprehensive systems information. If you forgo one or more of these three critical elements, failure is predictable even before you begin a repair task.
The most basic and simple error; Failing to assess the battery rating and cell condition. Note I didn’t focus simply on voltage. The first example was a Ford Focus 1.6 ecoboost, suffering windscreen wiper failure. The car was driven to us, and the customer explained the battery had gone flat and been charged.
Conductance test
I began with a conductance test with my personal Midtronics MDX 600. Voltage was 12.47, rated 540 amps, however it only returned 346 amps. Please refer to Fig.1. I ordered a replacement and decided to continue testing the screen wiper problem. The vehicle started and drove into the workshop, so I began checking voltage and ground at the twin wiper motors. There was no change of state, however the voltage was below 9 volts after only a very short time. So, I fitted a temporary good battery and continued with my tests, only to find the wipers working normally.
The explanation is straightforward; CAN and lower priority networks often hibernate with system voltage drop. So, my knowledge, process and tools won the day here. The next problem, another Ford Focus, had much more challenging issues. Initially it drove to us with starting problems, then failed to start.
Global vehicle check
I began with a global vehicle check using the garage TOPDON serial tool. It had reasonable systems access and displayed steering column communication loss with the body control module; B1026:87-2F. It showed two keys stored, and the immobiliser was registered in the PCM. We had limited wiring access via E3 tech data, but crucially no test plan data. We were dead in the water now, relying on the common-sense method. We decided to ramp the vehicle and examine wiring and PCM, located we thought under the front wheel arch.
The PCM housing was damaged, probably from a light frontal impact, and had allowed water ingress. The next series of events taken over several weeks is a textbook example of how to fail in a repair and diagnostic process. My only satisfaction was that the decisions were not of my making.
The cost of a new PCM with programming and coding exceeded £1,500. The owner could not afford the repair, so a second-hand PCM was suggested. Mistake number one; Cost must never influence correct process.
A unit was sourced by the owner in Poland. Mistake number two: Never allow customer interference in the repair or part procurement process. The owner was instructed to send the original PCM to Poland so programming and coding could be transferred across. Mistake number three: Never use or trust third party contractors unless personally known to you. Although this is technically possible, and we at ADS have done this many times, you have now lost control of the repair. This mistake is fatal and has no comeback.
The PCM was fitted to the vehicle and guess what? No change in the symptoms. I was then re-tasked to check the fault from the sketchy wiring schematics. I had no enthusiasm left at this point, so let’s score it as mistake number four; You need to have a positive mental attitude. My evening’s Vodka consumption didn’t help. Having exhausted all limited direction of diagnostic enquiries, it was time to put the train back on the tracks.
Please refer to Fig.2.
I consulted a local friend and expert, Paul Emmett from Reedley Service Centre. This was correct decision number one. He owns the Ford IDS platform, with which one can programme and code the PCM. Following this process, the keys operated the central locking, and the instrument cluster became active. Despite this apparent progress, there was still no cranking. As part of the coding process though, a global scan was conducted, resulting in a curious and previously unknown error. It turned out that both rear wheel speed sensors were defective. Paul suggested replacing them before continuing; Correct decision number two. The sensors were replaced, and the vehicle started normally with all stored codes cleared. I place this explanation in the same column as my previous observations. In short, wheel speed sensor errors are broadcast on high speed CAN, therefore the error frames must have corrupted the network, thus preventing crank start.
The failure to understand this I put down to incomplete serial data from TOPDON.
I am sure I don’t need to recap events, and I am not going to expose the decision makers, but as the technician in question I should have refused to continue. This was mistake number five. I don’t know what the owner was charged for the repair, but I hope it was more than the original estimate.
Challenges
Let’s end on a little restored personal pride; A Ford Transit Connect with a faulty power steering assist system was presented, with a blown 60amp control fuse for good measure. Challenge number one; Ford would only supply a complete vehicle wiring harness for £600 despite the auxiliary fuse panel being easily replaceable. Please refer to Fig.3. I decided to replace the fixed fuse assembly with the correctly rated value and conduct current flow analysis by logging serial data and directly using my personal fluke clamp. Current peaked at 65amp for a few milliseconds. Average current flow was 35amps. Please refer to Fig.4.
I was made aware of known issues with steering rack faults, and I am waiting to see if the fault reoccurs, which will mean a new rack assembly is required. This customer has no issues with cost.
I have archived many examples of good and challenging decisions facing technicians with limited access to essential assets. More next issue.
- VW Van vibes
While preparing this month’s topic, it occurred to me that a short explanation of the process behind the scenes would be helpful. All the topics I have presented here over the years have been prepared from real issues we have been presented with in our workshop. This guarantees authenticity and technical credibility.
The topic for this month is focused on a VW T5 van suffering severe vibration. I will begin by explaining that no repair authority was given at the conclusion of the diagnosis. The decision was based on a value versus repair cost and not through any disagreement. All cost was paid without objection.
The owner is a customer known to us. He often uses the vehicle for long journeys over extended distances between Lancashire and Cornwall. It was while down in Cornwall that the problem of vibration that brought the vehicle back to us began. The vibration was present with the engine running. In addition, it displayed a change in tone and reduction of intensity when full steering lock was applied.
While in Cornwall, we understand that a new alternator and power steering pump was fitted with no effect or reduction of vibration. Following this work taking place, with no change to the problem being seen, the decision was made to drive the vehicle to his regular trusted repairers. I.e, us! This was brave to say the least, and potentially teeth-rattling for the duration of the drive back up to Preston.
In an odd sort of way, the diagnostic process had already begun as the van did in fact reach us, and did not display any additional problems. Power delivery was reported as normal, suggesting that the primary rotation engine components were working normally. Our initial checks were visual with a full serial evaluation showing no reported errors. The problem appears to be mechanical in nature with no collateral influence.
Before discussing the laws of physics when applied to a motor vehicle, why don’t we explain exactly what vibration is, and how it can escalate end cost if not accurately diagnosed.
Vibration is mass energy from a source, taken through the transfer path to a respondent. Not only is this wasted energy that could be converted into traction, it will also lead to premature component failure if left to continue.
Vibration is experienced in three ways; feel, sound and sight. How we experience it depends on the amplitude and frequency. High mass energy occurs at lower frequencies and is more likely felt and heard. Low mass energy occurs at higher frequency ranges often felt and seen.
Traditionally vibration has been diagnosed based on opinion rather than evidence. So, what’s the problem? Finish reading this article then you will understand the problem and risks. Vibration can also be affected by the transfer path and respondent. For example, a high mass vibration may be amplified by a light body panel or vehicle trim.
NVH
To succeed with NVH you must first forget you are working on a specific system and focus on frequency and amplitude. The motor vehicle is a series of mechanical systems in permanent conflict, a little like a modern marriage!
There are multiple components with mass differential (weight), vector conflict (direction), frequency (speed), and amplitude (volume). The Pico NVH kit uses a three-dimensional accelerometer and microphone, or multiples of each. They convert mass into a pictorial graph, bar chart or three-dimensional topography.
The primary requirements are engine speed via the serial port or optical input, transmission ratio data, and tyre size. With this information, the software will distinguish the area of responsibility along with any collateral transfer path and respondent frequencies. Further discovery is possible by entering individual component rotation ratio, for example power steering pump.
Physics lecture over. On to the T5. We did not need to enter tyre size as the vibration was present simply with the engine running. Crankshaft data came via a Mongoose serial interface with the accelerometer mounted directly on the engine.
Referring to fig.1, the left scaling is mass in milli gravity, the base scaling is frequency response.
E1 represents the crankshaft, E2 represents combustion mass. The cursors represent the number and ratio of events corresponding to E1.You can easily see that the vibration in the centre of the graph has no relationship with the crankshaft frequency or combustion events. That the frequency is higher (lighter mass) than E1/E2. Now we need to evaluate the engine mechanical ancillaries. These are driven by a complex gear train at the rear of the engine.
Looking at fig.2, note that the tension sprocket housing a counter rotation spring arrangement. Now for the maths based on the gear train ratios; The alternator ratio 2.62:1, power steering/air conditioning 1.59:1.
Now examine fig.3 to see the revised image. E1 frequency 13hz x 2.62= 34 hz, so vibration is caused by the alternator mechanical drive system. There is a drive shaft and cush drive coupling which transfers drive to the alternator. The secondary event at 66.6hz is a respondent event, probably body vibration.
Conclusion
Now for the knockout punch! The tension gear sprocket is not available separately; in fact, you must buy the complete short engine. I seem to recall David saying it is £5,500, notwithstanding the labour cost to build and fit into the chassis. Hence uneconomic repair diagnosed without any intrusion whatsoever. Diagnostic time 0.5 hours plus the ubiquitous coffee break.
Convinced? Join our NVH training programme. Or pay me and I will come and listen to your noises.
- Process not problem
Frank’s ongoing look at the recalcitrant VW Golf R serves as an example of why process will win every time
- Setting the bar high
Where were we? I’m wondering that myself, so I will begin with a recap of part one, along with an honest critique of what has gone up to this point. So far, the following parts have been replaced; Four spark plugs, four ignition coils, high pressure fuel pump, and #1 high-pressure injector.
The phrases ‘dirty washing’ and ‘public’ come to mind. Despite what I always tell you, these parts were replaced as a result of a reaction to the symptoms and not as a result of thorough data analysis.
We understand, with confidence, that the fault is due to a lean fuelling condition, but we do not understand the cause. I do, however, have a high degree of confidence it is not a hydraulic-mechanical injector fault, following the ASNU bench test.
David G and I took a step back to review our approach and plan a way forward. Using VCDS, we elected to monitor critical events from crank start through to hot idle. Referring to Fig.1, please note there were no initial issues during at first, then quite suddenly after 30-50 seconds, you will see what happened, coinciding with the onset of combustion error. High pressure is a touch low though.
Moving onto Fig.2, please note the drop in high fuel pressure. At this point it is sitting at 45bar. This is not correct, so why do request and actual match? Has the PCM in error calculated this as the correct value? Or is it an incorrect load value from a sensor, wiring or environment? Maybe it is a PCM internal fault? Experience generally convinces me it is not the PCM however.
Evidence
Let’s discuss the evidence, while also keeping an eye on the camshaft timing which I alluded to in part one last month.
From cold, the exhaust camshaft increases its lift by approx. 0.6mm and adopts an advance angle of 35°. The inlet remains at zero and does not have any lift function. As a point of interest, you should hear a distinct click from the cam housing when full exhaust lift ends together with a sudden reduction in open angle. Consult data frames to see what I mean. This occurs normally after approximately two minutes. Please also note the change in exhaust cam timing to 2.8° actual 4.0° specified. The inlet now adopts an angle of 15° actual and specified.
Moving onto Fig.3, the data displayed shows values from the engine mid-way through the warm-up cycle. The engine is still fuelling from the high-pressure system. The high pressure has now deteriorated to a mere 35bar, and 50% of the nominal expected value. The lean combustion problem is now extreme with misfire count increasing dramatically.
We now reach Fig.4. Finally, after approximately 10 minutes, the PCM reverts to port injection. This can vary dependant on environmental temperatures and engine speed and is accompanied by a more prominent click from the exposed port injectors. The engine now recovers its combustion composure, with the useful visual evidence, high pressure increases to 90bar. The reason for this is to prepare the high-pressure system in readiness for any instant high load demand. Keep this information in your pocket until later.
Assessment
With all this information available, what is my assessment? It is a fact that the only route for fuel to enter the engine combustion chamber is via the lateral feed injectors. The only explanation for incorrect fuelling quantity is a control deviation due to a circuit fault, physical hydraulic-mechanical injector fault, or a PCM calculation error.
Having previously expressed confidence in the hydraulic-mechanical injector function focus transfers towards the PCM fuelling feed back system, the Lambda sensors should theoretically provide all the critical answers we need.
Just to fill in a few gaps before you all go dashing to the internet blog sites, we did conduct exactly accurate injector current profile analysis. The ultimate PCM injector control is fuel pulse time and current path. Using Pico scope and a Hall Effect current clamp, we monitored the injector function together with high rail pressure. We noted no discernible change in injector control when witnessing a rail pressure drop.
Please refer to Fig.5 for this. Blue/black trace represents the injector current path across two injector circuits, with both homogenous and stratified events visible. Green trace represents the PWM control for the high-pressure actuator. We continued monitoring current and rail pressure until the moment port injection took over. Looking to Fig.6, blue/ black trace in this instance represents the current path to the direct injectors, while the red trace shows the seamless transition to the port injectors.
Coming up
Keeping up so far? Well, it’s not over yet. Part three will discuss the response of Bank1 Sensor1 function and response. This will be conducted through direct current measurement, with Pico and serial data via VCDS, paying particular attention to fuelling correction.
Now things are going to get very interesting. What you are expecting is not going to happen. Exciting isn’t it? Good enough for a direct-to-Netflix action movie, or even a mini-series? See you next month.
- Inject some knowledge
At the heart of fuel delivery is the injector. If there is a single focus point that has helped reduce emissions and boost performance it’s the injector. Despite this, we don’t pay it enough attention, and I include myself in this critique. Let me qualify this by asking a rhetorical question; How many of you have injector bench test capability?
I do, but freely admit to not giving it a more prominent position in fault diagnosis. I am going to expand later just how intrusive testing should be conducted. To begin, a short trip down memory lane won’t do any harm in understanding basic problems.
Injector problems started in earnest when lead was removed from gasoline. The Nissan 1.8 turbo and Austin Montego 2.0efi were two of the most problematic examples. Both used 15ohm single event saturated triggering with approximately 1-amp peak current. This was back in the days when we were not measuring current nor did we have an injector bench.
All the diagnostic evidence came from the 4-gas analyser. CO and O2 should balance at approximately 0.5%, as this will achieve a near perfect lambda 1 ratio, 50-100, CO2 at its highest at around 17-18%.
A lot has happened since then. The key to ideal fuelling is in reducing the lag or dead time in injector response to PCM control. As engine power increased and turbos became almost mandatory, more fuel was required. To achieve these aims, opening times were increased to a point where they were in danger of colliding at high engine RPM. We are still talking port injection here, fuel pressures crept up to four-bar and high flow injectors started to be introduced.
Current ramping also changed to peak and hold with peak values of around 4-amps. For the time being things stabilised, with little or no obvious common injector problems. The next challenge manufacturers faced was to reduce the internal mass of the injector components. In plain English they got smaller, lighter, less robust, and with lead free legislation less reliable. Remember Fiat iaw injectors?
Precise control
As EU emission rules became more stringent, the need for even more precise control was inevitable, and along came direct high-pressure injection. Lets explore the variables of fuel transportation, variable delivery pressure 50-200bar, multiple injector strikes and adjustable delivery timing. Peak current now reached 10-amps and pwm switching became commonplace.
We now have gasoline injection that more closely resembles diesel injection protocols. They also bring similar problems. Fuel is no longer delivered through the inlet port, leading to a build up of carbon behind the valves. This effect, the critical swirl in the cylinder, is essential for complete combustion. Filtration and fuel quality are now major considerations for reliability.
Hostile environments and anomolies
Injectors are now mounted in a more hostile environment, more pressure, more heat, more tip carbon. So, the need for testing and cleaning has come full circle from the lead-free era. A major problem here is the stress caused to the injector body by techs not using the correct removal tool.
Remember the comments on lighter internal mass; This means than bending stresses during removal leads to intermittent combustion anomalies. I do love that word, it more accurately describes incomplete combustion, often without any credible serial fault data.
New fault phenomena
Now let’s notch it up a bit and introduce some new fault phenomena. The internals are so light they can suffer mechanical failure, and the closure spring can break. The internal filter basket has been moved to a more central position, resulting in inaccessibility for replacement.
