Fiat Kobelco E135 | Fiat Kobelco E135 Excavator - Engine shutdown

Ben Martins
February 26 2018

Hello Andy,

Thank you for raising your questions and I will try to answer them as best as possible. With regard to the 5V oscillation, honestly, I don’t know. It could be down to a number of things and as you’ve pointed out, all after the solenoid has been turned on. The lack of technical information really does hinder the diagnostic approach in this case and not having a wiring diagram to utilise again makes things very difficult to analyse in any real depth. It could also be there are number of solenoids that are activated on the hydraulic side of things in preparation for engine start. Some hydraulic pumps will allow the engine to start up under no load conditions and so will activate the position of the swash plate to prevent this. I’m not saying that this is the case for this particular machine but it is something to consider during an ignition on event.

You are correct that the second image the engine is started and running and I can see your point about current dropping once the engine has started. It could be that there is a higher resistance or it could be that the solenoid doesn’t need as much current to hold it open. This is a purely a theory in my head and I’m not disregarding the possibility of a volt drop due to the vast amount of metal work, the cables and the age of the vehicle but what if the pump drawing the fuel will help to overcome some of the spring force of the stop solenoid. If there is a fluid flow through an orifice then a thought would be some of this ‘work’ will be exerted on the stop solenoid and therefore less current will be required to hold the solenoid in the off position. As I said I do need to prove this and it is just a thought in my head but trying to find some of these older type engines can be a little tricky in a world of Common Rail! As I said a voltage drop certainly isn’t something to disregard but before I was asked to take a look the previous stop solenoids were checked which all had open circuits after the machine had stopped. If there was a lack of voltage to hold it open then the coil windings would still be intact.

We really do appreciate all the feedback from the case studies and often we discover new techniques and new ways of looking at the data we see in the vehicles we face.

Kind regards

Ben

Ben Martins
February 26 2018

Hi Richard,
Thank you for comments and I’m hoping that I can bring some more 24V systems as you’re right it, isn’t something we see very often and not something I’ve been exposed to for a number of years!

To answer your question on rectification, in theory there shouldn’t be any real difference. The alternator is fundamentally the same in operation. I think I’ll need to carry out some further tests on 24V systems to see if this is the case and if the ripple we see in the captures I acquired are the same. The other issue surrounding this particular machine is the length of the earth from the battery to the engine. There is a lot of heavy metal between the earth points which could lead to some interference and possible alter the signal we would expect to see. Again I will need to get some further captures and have some comparisons to be able to fully answer your question.

You are correct in saying that the output is from the positive aspect. I think it is important to remember that when we AC couple a channel we are removing the DC offset to just show the ripple on top and reference around 0V so whilst it would appear that there the voltage appears negative this isn’t the case. There is a lot of discussion as to whether we need to AC couple at all and as always there are pros and cons to both. The AC signal is always present on the DC and there is an easy way of proving this. If we captured battery voltage using both DC and AC coupling with a vehicle running and apply filtering to both, then if we increase the scaling of the DC channel to say 50 times you will now see the AC ripple on top of the DC signal. This requires a lot of work and when it looks like the snow is about to fall, time was more important to me hence the need for AC coupling.

Sadly I didn’t capture the current output there a number of reasons for this, one being the weather! Hindsight is a wonderful thing and if I could do it again I would have measured current but with these machines the luxury of a nice dry workshop isn’t the case and time was very much against me. Because the fault was as intermittent and unpredictable, I was looking for things that were different and out of the ordinary. When machine showed the fault in rectification there were no additional loads being applied, it wasn’t anywhere close to being at operating temperature but I completely agree with you, a sudden demand for current can cause diode failure. With the lack of additional loads and the inconsistent un-rectified signal I made the call on the alternator. As I mentioned the operator has reported the machine is still working as expected since the alternator has been replaced.

As always we are learning all the time and it is good to see questions being asked.

Kind regards
Ben

Andy Rogerson
February 14 2018

Hi!
there is lots of information in the traces that hasn’t been discussed that make me question the conclusion that was drawn. Some more information would be helpful.
In the first trace, there is a +/- 5V voltage oscillation after the solenoid is actuated.  Any suggestions what the cause was?  There is another similar but not quite so large voltage dip earlier in the trace too. At this time, solenoid current was 950mA.  Of course, the alternator wasn’t’ charging at this time.
It isn’t clear where abouts on the 2nd trace the engine started.  I think we can assume it was before the displayed trace started as the battery voltage was higher than the earlier trace.  The solenoid steady state current at this time has now reduced to 680mA.  this is limited by resistance in the circuit.  What is the cause of this increase of resistance?  If there is unwanted resistance (and therefore volt-drop) in the circuit, there could be insufficient voltage to reliably operate the solenoid
In the third trace, why the need to use AC coupling, rather than just zoom the voltage scale onto the DC signal?  The shape of this waveform is dependent on the high pass filter applied to the DC coupled signal.  As you’ve demostrated, the signal is distorted relative to the real voltage (DC coupled).  I don’t think we can see any alternator ripple within this waveform, at this timebase.  As already mentioned, the positive/negative spike is a function of creating the AC coupled signal.  Using a zoomed version of the DC coupled trace is a much more reliable image to interpret.  The current remains about 0.7A, so much lower than the original trace. 
You’ve talked about excessive current leading to coil burn out, but the current with engine running is much less than with engine off.  This then implies low voltage across the solenoid rather than high voltage that you are proposing as a cause.  Low voltage across the solenoid coil can of course lead to failure to operate the coil.

Richard Lukins - FioranoCars
February 03 2018

HI Mike and Ben
Another interesting and obscure failure that would be near impossible to find without a scope, and a classic case of symptom verse cause throwing the mobile tech. Well done for identifying the issue.
However, a few questions/comments, especially as I don’t see much 24v 😊
1. On future posts, could you try to scale comparison screen shots to the same settings, it just makes reviewing them easier 😊 (both time base and measurement scales please)
2. The ripple is nothing like the rectification I’m used to seeing on a 12v system (series of 3 almost perfect elliptical crescents to the positive), on either the before or after shots, is this typical of all 24v systems? In terms of both the shape of the signal (almost square rectification), and the lack of being able to identify the 3 phases?
3. The positive element of the AC appears, visually anyway, to be very low, say under 5% duty (on the New waveform), so surely this indicates the amps output would be pretty low too? Don’t we only get DC Current (amps) from the positive element of the post rectification A/C signal? Sorry if I’m missing something elementary, just trying to understand this clearly different system from those I’m used to!?
4. Did you capture amps output from an alternator, if so was there an extra demand being made/output which correlated to the sudden rectification failure? We’ve seen issues relating to amps (from inrush of motors like fans/pumps) putting a sudden load on the alternator and allowing weak/failing diodes to then fall over, so we always test the output amps with DC voltage and A/C ripple to understand better the alternators characteristics and any issues ... a one second fault time could correlate to a “inrush”, and that might identify the true root cause, and show the alternator is failing as a symptom due to a long-term “inrush” issue damaging it? Something to consider should the new alternator fail?!
Thanks for another great example of Pico’s capability
Best Richard

Ian Petersen
February 01 2018

Excellent detective work.  A story to keep in mind when working on older supposedly ‘no electronics’ machinery.  Even the humble alternator has enough electronic components to cause odd issues if ever the smoke escapes from them…

Stuart Dawson
January 31 2018

Thank you for really great informative review. You are so right about going back to basics, I also always have a tendency to over complicate things, especially with all the different technology we have now… really good example of good thought, basic diagnosis. Thanks!

Martin Rubenstein
January 31 2018

As ever, a thoroughly fascinating read and another interesting lesson in diagnostics and the power of the PicoScope.