It’s all very Scopetastic!

John Batten points out the magical power contained in the scope that could be helping you with diagnostic spells every day

By John Batten | Published:  02 April, 2018

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.

Whilst I’m not sure that it’s possible to reach a Zen state in this industry (please let me know if you’ve attained this), it was great to discuss the various paths a technician has to choose from once they’ve decided to continue their technical advancement.

The available options are obviously specific to the individual. That being said my catch-all mantra is to always take the path least travelled. Why would I not advocate an easy path? Well, as with most things in life the route of least resistance may throw up the odd quick win, BUT it rarely delivers the long-term results that pay the kind of dividends we dream of and it’s with this in mind that I scribe this article.

Where’s the map?
Every technical adventure should start with a review of the map. Whilst our diagnostic process will make plain the waypoints on your route to the first time fix, there are many twists and turns along the way where our hero is forced to make a decision. The quality of these decisions will ultimately see their journey culminate in glory, or see them lost in the maze of misery that is misdiagnosis.

A little dramatic I know, but there’s nothing like a bit of emotion to brighten up what would otherwise be just another technical article. Back to the adventure…

If Harry Potter did diagnostics
With so much at risk, what are the critical choices our hero should make? Possibly the most important decision for a technician is to truly understand the relationship between Volts, Amps and Ohms. I’m not talking about the theoretical math that underpins Ohms law, not that it isn’t important. Just that it’s not as important as understanding the fundamental relationship between those values when it comes to using the tool that will quite frankly change a technician’s career forever.

What tool I here you cry? It’s a bit like the Elder Wand (apologies if your not a J.K. Rowling fan). Difficult to find the right one, not the easiest thing to use, but oh boy once you’ve had a bit of practice it’s possibly the most powerful diagnostic weapon in your arsenal. If you’ve not guessed it so far then you really need to get out more. I am of course proclaiming the need for a scope.

Is it really that important?
In one word, yes! Think of it this way. If you’ve ever replaced an electrical component and it didn’t fix the car, then quite simply there was a test that hadn’t been carried out and the tool of choice in these instances more often than not is an oscilloscope. It’s not important which one you own, just so long as you use one that’s suitable for the job at hand. After all a scope is no more complex to connect to the circuit than a voltmeter and with a little guidance and practice on your part I’ll show you how to reveal faults that can elude technicians that give this tool a wide berth.

Let’s do battle
OK. So I’ve piqued your interest and now I have to make good on my promise. See what you think to this.

The battleground for this adventure is a petrol Vauxhall Insignia and the customer has reported rough running. The MIL light is on and glowing brightly, codes have been pulled to reveal a list as long as my arm and upon lifting the bonnet I’m almost blinded by a very shiny coil pack. The vehicle is quite obviously running rough and deserving of the many fault codes. So where to start?

There are a host of options open to a technician at this point. I decided to see if the rough running was isolated to one cylinder or whether it affected multiple cylinders. I used a serial tool to carry out a cylinder balance test whilst monitoring rpm to assess the contribution of each cylinder. I found that number four was making little contribution to the overall performance and set about finding out why.

Bring out the wand
The magic here is all in the tests. The tests for a routine diagnosis like this are straightforward and quick to apply. At this point I’m looking for diagnostic direction and keen to isolate the fault down to a mechanical, fuelling or ignition issue. A relative compression test bore no fruit; neither did my low down and dirty stress test on the ignition system. The weight of probability at this point was tipping the scales in the direction of a fuelling problem. It’s worth mentioning that whilst I have a love for scopes I won’t use one just for ‘scope sake.’ It needs to be the right tool for the test at hand. It’s very interesting though when the planets align and you see Ohms Law come to life through the eyes of a scope and that’s what happened on this vehicle.

So it looked like our rough running was down to fuelling on one cylinder and I was keen to discover if this was an electrical fault with the injector circuit or something a little more sinister. I used three channels to inspect the injector. CH1 – supply voltage, CH 2 – injector switched ground control circuit and CH 3 for current in the circuit. As soon as I had a stable waveform the problem was there for all to see.

Ohms Law + a scope = The answer
Whilst I could have used less channels to draw out this conclusion each one helps to paint the picture. We can see that channel 3 (see image) on the faulty injector circuit (point B) has a lower overall current level than that of the good injector (point A). This is affecting the reaction time of the pintle, and whilst it doesn’t look like much at first glance when cursors are used it shows a 20% difference. This reduced current was caused by an increase in resistance in the injector voltage supply.

Hey presto, the answer on a plate and all in a timely manner. Not much not to like about that. Further inspection revealed that injector harness had been damaged and the vehicle was restored to good health once repaired. You do have to love it when a plan (a diagnostic plan) comes together.

Cutting your way through the maze
All being well you’ll see the benefits of a little electrical knowledge and how using an oscilloscope can reveal this kind of fault like no other tool can. This type of testing isn’t ‘electrickery’ and IS within the reach of all technicians that have the will to
take the right fork in the road. It’s all very scopetastic!


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    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
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    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?



  • Part ONE: Employers in the firing line  

    Before July 2013 individuals were free to bring Employment Tribunal claims. However, in July 2013 the government introduced Employment Tribunal fees for anyone wanting to make a claim or appeal a judgment.

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    Supreme Court decision
    It appears that while claim numbers were dropping, unrest in trade unions was growing and so Unison decided to challenge the government’s implementation of the fee regime, claiming not only that it was unlawful but that it indirectly discriminated against women.

    Chloe says this was not by any means an easy task as both the High Court and Court of Appeal rejected the claim. “However, at the end of July 2017, the Supreme Court quashed the tribunal fee regime giving judgment that it was both unlawful and indirectly discriminatory.” Effectively the Supreme Court decided that the government acted outside its powers when it introduced fees at current levels, because the fees effectively prevent access to justice.

    What does this mean?
    The ruling means a number of things. Chloe explains: “As a result of the judgment no further fees can be charged by the Employment Tribunal until a replacement scheme is introduced.” This means new claims can now be brought for free again and no hearing fees will be charged claims already lodged.

    She adds that as for those who have already paid tribunal fees, the Ministry of Justice has undertaken to reimburse fees already paid.

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    fees prevented them from bringing a claim.”

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    With time, if a new fees regime is introduced and once the media attention has died down, the number of claims will level, but, in the meantime, employers must watch and wait.



     


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