One waveform One picture

Ask for and share advice on using the PicoScope kit to fix vehicles here.
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Re: One waveform One picture

Post by ben.martins »

Luckily for me I get to head out to some of the more interesting cases where we can use the scope. This one was no exception as it's something I've never worked on before - a crusher!

The purpose of these machines is to do just that, crush large lumps of rock and concrete before feeding into a screener which would separate the different rock sizes and deposit them into their own individual piles. To see what these machines can do please see the following video -

The reason for visiting is to determine the cause of an intermittent cutting out. It would then start up again with no issue before randomly cutting out again.

For those that have read some of the off highway case studies we've been, you will have read that technical information really isn't that easy when it comes to this type of machinery. The issue being is that the machine may come with one manual but the engine would be made by someone else. This machine was manufactured by Extec but the engine was made by Deutz. Having to look between to different drawings was fun, especially as the wire colours didn't match the machine and made worse by the fact the weather was not on our side!

Fortunately, the technician I was supporting had a much better idea as to how these machines operated than me, with the main focus being towards the EPU - Engine Protection Unit. As with a lot of plant machinery there is often additional protection circuits fitted to the machine in the event that something is going horribly wrong, they can be switched off quickly. This ECU is designed to protect the engine should it overheat, stop charging, suddenly develop low oil pressure and more. These crushers are typically left to their own devices and once running continually operate till their work is done. Having something to make sure the engine doesn't destroy itself is vital, especially as it's the only way you can move these things!

The problem being was we didn't know what the ECU was doing in order to shut the machine down. Looking at the connector we had 8 wires which meant bringing out the 8 channel scope. When it comes to this type of environment I try to steer clear of the 8 channel, as dealing with all those test leads in the rain and mud is not fun. However, it comes into it's own when you need to understand how circuits interact with each other.

With the machine up and running and all 8 channels connected, we started with a wiggle test and fortunately the machine cut out when we lowered the electrical panel lid. Pulling on the wiring we then located the issue being a power supply not correctly installed into the electrical board and the terminal screw was actually loose.
Granted, I know this should be one waveform, one picture but I didn't have the one picture to give the best impression!

Using the 8 channel scope we could see that when all is well with the machine, 7 of the wires should be at battery voltage (or close to) with one of the wires at 0V (possible ground). They should stay at a high voltage till a sensor is grounded or has an open circuit. At this point the protection ECU can trigger the emergency relay which then shuts the machine down. This was proven by ground one of the wires in the connector with the machine running which as expected, shut the machine down.

As with everything we try to diagnose, understanding how it works is paramount to understanding how to diagnose it. In the event that technical information isn't available being able to see the interaction between circuits can be extremely useful which is where the 8 channel scope shines.

I hope this helps

Steve Smith
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Re: One waveform One picture

Post by Steve Smith »

It has been a while since we posted here which is not for the want of trying. Like us all, there are not enough hours in the day to do everything

I quickly wanted to share this one as it was a fault that raised its head on my own car!

2013 BMW 320 d Touring (F31)

Engine warning light on accompanied with loss of power (Minimal boost from the turbo charger)
Once the engine had cooled, the vehicle performed as normal until hot, where the symptom returned

Fault code:
25D100 Boost pressure sensor Short to ground
27F100 Charge air hose Hoses faulty

A brief inspection of the air intake confirmed no leakage or connection issues

As always, when it came to diagnosis, the fault was illusive and required considerable testing before I could confirm the output from the boost pressure sensor was at 0 V (hot engine) with serial data reporting a fixed “charge air pressure” of 60 mbar regardless of engine speed/load or minimal boost applied
Note: Sensor “power & ground” were good when “signal” at 0 V

So, there you have it, replacing the boost pressure sensor resolved the issue but it got me thinking, “how could I speed up the diagnostic process?” rather than having to wait for the optimal engine temperature for the fault to occur

This was one of those moments where you answer your own question, “by applying an external heat source to the boost pressure sensor”

I know it is not rocket science but simulating symptoms mentioned by the customer or displayed in freeze frame data “theoretically” should reproduce the fault condition

Using the Universal break out lead set ... t-lead-set below, I have supplied an external 5 V & ground to the sensor whilst applying heat until the fault revealed itself
Image 1
Image 1
Note; when the sensor cools, how the output signal was restored, exactly as per the symptom

I know there is never enough time to conduct such investigations in the real world, but the technique can be applied to components in situ, be that with an external heat source, freezing/moisture sprays, or wiggle testing

“Food for thought” as ever and sorry the One-Waveform-One-Picture has not been strictly adhered to above (i.e., 3 images used, hopefully revealing the relationship between output signal and temperature )

I hope this helps, take care…..Steve

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Re: One waveform One picture

Post by Rfmotors1 »

Hi All,
I would like to share one case here on this thread created by Steve as it probably matching the "One Waveform One Picture" criteria, hopefully it's OK.

We had Toyota C-HR interesting complaint in the workshop and the Pico WPS500X transducer showed the potential where all other common methods did not help. Decision based on the result of this test was to replace engine for second hand instead of trying to repair it. (leaking valve would lead to repair for example)

COMPLAINT: Customer complained the engine vibration especially at idle and the diag tester showed misfires on cylinder 3. The shop swapped coils, plugs and injectors with no fix.

PREVIOUS DIAGNOSIS: The cylinder analogue compression test result was 6 Bar on cylinder 3 and other cylinders were 10-11 bars at cranking with TB wide opened. The in-cylinder leak test did not reveal any leak, all cylinders had only about 10 to 15% leaking which was good result.

PICO TEST: Engine at idle, pressure transducer in cylinder 3 and then 2, each at one time. Good cylinder 2 RED overlayed with bad cylinder 3 GREEN reference waveform for comparison.
Pressure difference 3.87 Bar, cyl 3 lower pressure but the valve timing was identical for both compared waveforms.
Cylinder 3 and 2.jpg
RESULT: The reason was bend conrod on cyl 3 resulting the piston did not compress the gas enough as it did not reach TDC.

Original waveform:
Cylinder 3 and 2.psdata
(3.83 MiB) Downloaded 73 times

Thanks for reading,

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