Tools to survive and thrive

John Batten takes a look at the art of diagnosis and the one tool to rule them all

Published:  11 June, 2018

My life as a business owner, trainer and technician is an interesting one. I was recently spending some time with a client after a course just shooting the breeze. You know the kind of thing, a cuppa, a cake and an hour just putting the world
to rights.
    
Part way through our conversation Matt proclaimed that I must be “living the dream!” This made me stop and think (something I’ve been told not to do by my wife) about how I am indeed very fortunate to have a career doing something I truly love.

Wading through treacle
Spending my days with like-minded business owners and technicians, helping them drive their careers and businesses forward. What’s not to like about that? Not much, but has my work life always been like skipping through meadow on a sunny day?
    
Quite frankly… No! Don’t get me wrong –  I’m a glass half full sort of chap and regardless of the task ahead I’ll give it my best and persevere until success emerges. However, on many occasions in my diagnostic career it was just like wading through treacle, and therein lies my point. To get to a place where you’re ‘living the dream’ you need wellies! Show me a successful technician and I’ll show you someone who’s great at wading. They’ve just waded long enough to build a versatile skill set along
the way.

The recipe for success
As with most things in life there are essential ingredients. With the right ingredients you’ll successfully avoid the diagnostic treacle swamp and swap this for a faster and more enjoyable repair experience.
    
“What’s this recipe?” I hear you cry. It has six elements that when bought together produce truly remarkable results. They are;

  •  The right technician
  •  The right tools
  •  The right information
  •  The right training
  •  The right practice
  •  The right process


The focus of this month's article being the right tools for your diagnostic survival.
    
I could turn this entire magazine into ‘Johnny’s must-have tool guide.’ However, instead I’ll focus on the
one tool that plays a huge part in troubleshooting success; Enter the oscilloscope.
    
Why am I so fond of this tool? When used skillfully it will quite simply change the way you look at diagnosis forever. I was speaking with Kris Gordon of Pier Garage (one of our training delegates) about this recently. He’s been making some great progress with his fault-finding career and mentioned that use of a scope and some practice has enabled him to “be able to mentally visualise what he should be seeing and the state of the circuit.” This is a sure-fire route to a successful and timely diagnosis. It just so happens that I made a similar discovery in my own career many years ago. Perhaps we’re onto something? But which scope should I buy?

Getting ready to dodge the Bullet
If there was ever a contentious subject it is “which is the best scope to buy?” Wars have been fought over less and in some parts of the world that battle still continues between the diehards in the red camp and the blue camp. I take a slightly more pragmatic approach. Let me ask you a question; How many ways do you have of undoing a 15mm nut? Take a look in your toolbox you’ll find dozens of ways to achieve that task. Why so many options? Different tools for different jobs and in many ways scope choice is no different.

The Search for the Grail
Like Indiana Jones I’ve been searching for the Holy Grail of scopes my whole career and I’m yet to find ‘The One’. What does my Grail scope look like?

  1. Minimum of four channels. Eight would be very cool
  2. The capability to easily build a waveform database
  3. Sufficient hardware specification; bandwidth, record length, samples, waveform update rate etc to accurately display fast frequencies over longer time bases
  4. Great software; A range of triggers, math channels, cursors, ignition analysis etc which will enable me to be creative with my test techniques
  5. Highly portable so I can move quickly and freely around the vehicle without the need to carry a laptop or push a trolley


If by chance you’ve found this illusive tool then I’d be grateful if you’d let me know, until then I’ll continue to use two scopes. A PC based scope for points one through four and a handheld for when portability is key or I need to invert myself in a footwell.

It’s worth bearing in mind that as the “one scope to rule them all” is yet to be discovered then you may need more than one to cover all bases.

I own a Scope – What next?
This is where the magic happens. They key here is to find a little time to practice and look at good waveforms. This, along with the most important questions you’ll ever ask;  “Why does that waveform look that that?" Followed up with a little training or research to discover the answer will propel your career to another level.
    
Take a look at the following example and I’ll talk you through the salient diagnostic points. Waveform 1 is a primary ignition waveform from a BMW 3 series. I’ve made a single connection to switched side of the coil with a full range voltage scale of 500 volts with 10ms across the screen. Let’s take a look at all the diagnostic information we can see from just one connection.

  1. Battery voltage. This confirms fundamental continuity of the positive supply. It is worth noting that as the circuit isn’t loaded at this point, a high resistance in this part of the circuit may not be visible. Another channel testing the coil supply would fix that though

  2. Coil turn on. The ECU has grounded the primary winding and current will start to flow in the primary. Dwell starts here

  3. Dwell time. This is the duration that the primary winding is held to ground. A magnetic field will be building, enveloping the primary and secondary windings. It’s useful to compare dwell across all coils. Discrepancies can indicate primary circuit faults and even ECU output stage issues

  4. End of Dwell. The control unit no longer holds the primary circuit to ground. The magnetic field produced in the dwell phase collapses inducing a voltage in both primary and secondary windings. This can reach many hundreds of volts. Discrepancies here are indicative of primary circuit faults

  5. Ignition burn time. I know you shouldn’t have a favourite, but this is my favourite part of the waveform. Here you can see the effect of mutual induction between the primary and secondary windings. The shape (for want of a better word) in this part of the waveform is indicative of so many variables within the cylinder. Items like plug gap, compression, mixture, cylinder sealing to name but a few

  6. Coil oscillations. At this point we no longer have enough energy to maintain the spark, the event ending with oscillations. This can be indicative of secondary issues

    
All of that and form just one connection. What’s more, I’m not finished yet. For waveform 2 I’ve changed the voltage scale to two volts full range. This enables me to gain additional diagnostic information from the same waveform.
    
Points 7 and 8 are the start and end of dwell, the ramp between them caused by the increase in current within the primary winding (I do love ohms law). Discrepancies here indicate faults within the primary circuit.
    
In summary, one quick connection and eight points of diagnosis that will increase not only the speed of fault identification, but will give additional certainty when it comes to root cause analysis. All this and I’ve only used one channel. Wait until you see what we can do with a few more!
    
If you’d like to know more about how to develop your technical team then call John at Auto iQ on 01604 328500. Alternatively why not attend one of our free online training events. To find out more visit. www.autoiq.co.uk/events




Related Articles

  • #TeamTextar looking for “teammates” 

    As the UK looks forward to this summer’s major sporting event, TMD Friction is putting together an international “Team Textar,” and participants can win prizes as well as have fun.

  • Clutch development intensifies at National Auto Parts 

    National Auto Parts has launched seven new clutch kit references, including two CSC kits, one SMF kit, three clutch kits and one service kit. The CSC kits are for Land Rover Defender 2.2 Td4; the SMF kit for Ford Focus MK3 1.6 TDCi (2010-); the three clutch kits for Fiat Doblo 1.4 16v (2010-), Honda CR-V 2.4 i-VTEC 4WD (2009-) and Nissan 350Z 3.5 280ps (2003-2006), while the service kit is for Ford Focus 1.6 TDCi (2003-2012). The new introductions bring the number of references to well over 1,200 for passenger car and light commercial vehicle applications, with around 98% UK car parc coverage.
    www.national-auto.co.uk

  • LEADING the team 

    Unless you are a one-man business, you will probably have staff to manage. The art of managing your team is one of the most challenging, but ultimately, one of the most rewarding

  • It’s all very Scopetastic! 

    It’s been an interesting few weeks here at Auto iQ HQ. After my last article discussing the merits of “growing over buying” technicians I received a few phone calls looking for my views on the most productive path to technical enlightenment.

  • Ignite your interest in ignition  

    This month’s subject was prompted by a recent conversation with a colleague in Australia. The conversation included an invitation to a technical festival in October, where it was said that ignition would be one of the subjects of interest. Many years ago, when I began developing our training programme, ignition was a subject of primary concern when diagnosing gasoline
    engine problems.

    This is a complex subject often not fully understood and often overlooked. Its vital importance recently became apparent in our workshop, when we were presented with two Audi rs6 engine failures. One failure has yet to be investigated the other suffered piston failure due to combustion faults.

    The increasing complexity of homogenous and stratified fuelling, split injection delivery and variable valve timing geometry has placed critical responsibility on ignition performance. Often within the diagnostic process there is no serial evidence of an ignition problem, or that what evidence is available is incomplete especially at the early stages of failure. The process has not changed in over 30 years;  You must scope it.

    Process overview
    So here is an overview of the process. Firstly, you must understand that it requires a specific amount of energy to completely combust the air fuel charge. Ignition energy is measured in joules, our task it to ensure the energy is created and delivered correctly. The primary circuit bears the responsibility of energy creation with current profile as the focus of our measurement. The secondary circuit has the responsibility of delivery, our focus is burn time and slope profile.

    I accept that both circuits have a shared responsibility at the point of induction where energy within the primary is transferred into the secondary. The physical challenge is the method of accessibility. With static or direct ignition it is often not possible to connect to the coil primary circuit, leaving the option of induction as the method of measurement. The primary will always have a power and switched ground, so current measurement using a suitable hall clamp is always possible.

    Diagnostic observations
    The four critical diagnostic observations in order of priority are:
     
    Ignition burn time measured in milli-seconds with a range of 1-3ms depending on ignition type. Do not assume length of burn relates to energy value Primary current profile with a range of 3amps (points ignition) 20amps static ignition. Note the expression profile, it includes rise time and rate of collapse Coil ringing, this is the resonance at the end of the burn event it represents the small residual ignition energy returned in to the coil secondary winding Firing line voltage, this represents the value of electrical pressure in delivering the induced energy to the spark plug electrode it includes all components in the delivery process

    You must also understand that the performance of the injector, cylinder turbulence, and mechanical efficiency forms part of the combustion process. Intake air temperature, pumping losses and fuel quality all affect the burn process. Let’s begin with the tool I distrust the most! Serial data is a good first look – there is some very useful information such as cylinder misfire count, ignition timing individual timing retard data, air intake temperature and exhaust temperatures. There may also be additional data on burn time and primary charge time, but I don’t trust or rely on it.

    So, out with my Pico scope. Connectivity can be a challenge, over the years we have built our own probes, however, if the manufacturers can run a circuit there you can scope it. There is a simple logic process.  Begin with burn time, look at the duration and slope it – It should be roughly parallel with the horizon.

    A rising line confirms a difficult transition of energy across the electrode. Lean combustion, glazed plug, cylinder pressure, plug performance. Cylinder turbulence.

    A falling slope represents the opposite condition; low cylinder pressure, fouled or shunting plug circuit, small plug gap. The burn profile should be relatively smooth, a turbulent burn path confirms difficult in cylinder conditions. It can and does point to injector fuel delivery problems especially if a sharp rise at the end of the burn time is present.

    You may appreciate now just how vital scope evaluation is.

    Primary current path confirms good power supply and the performance of the power transistor in its ability to switch and hold load to ground. Note the rise time characteristics and the off switch, under shoot here is a good indication. If you can, observe primary voltage. Note the slow rate on load, it’s the slow rise in voltage during coil charge time, a problem here will affect current flow so go for current first its easier to understand. Remember one of my core diagnostic rules; If it moves, gets hot, or applies a load measure current!

    Coil ringing is the inverted energy returned into the coil secondary. With no path to ground,  it gradually gets weaker, converting its energy to heat. Expect 2/3 rings in current systems. If the coil windings are compromised in any way a reduction in inductance will follow. The rings will disappear, ignition energy may still be present but a reduction in value will result. Be warned this condition will never be known if not scoped and critical engine failure often follows.

    Firing line voltage can only be measured accurately in primary to be honest. Expect the following values:; Conventional rotating ignition 50v, wasted spark ignition 40v, direct ignition30v; Plus or minus 5 v on all values. The problem with exploring this with a coil probe is that the probe attenuation is not known, so its difficult to scale.

    I hope this helps. It is a very complex subject , often neglected and overlooked.

    Just before I go here is a challenge; How many information systems, VMs especially, don’t give these four  vital statistics? So how do they know if there is a problem?



Most read content


Search

Sign Up

For the latest news and updates from Aftermarket Magazine.


Poll

Where should the next Automechanika show be held?



Facebook


©DFA Media 1999-2018