This month we have a troubled Toyota Hilux, from our very own Steve Smith.
"When it comes to diagnosis there has to be a logical approach at all costs without any preconceptions about "What could be and what has been?". The subject vehicle in this case study demonstrates the application of such a philosophy. We have the arrival of a barely driveable Pickup truck; after the classic scenario of a trader purchasing the vehicle at an auction as a runner. To clarify, the vehicle in question was a 2007 Hilux 2.5 Diesel Manual with 145000 miles and looked like it had lived in a quarry for most of its life. The running symptoms were numerous with warning lights flashing, engine start and stalling, severe engine rattle under brief running conditions and excessive smoke via the exhaust. So where do you start? It has to be the beginning.
The all-important customer interview reveals all the answers that can help with some form of clarity when carrying out the initial assessment. The customer had mentioned how he had viewed the vehicle days before at a local auction but it would not run. An auto electrician was called and miraculously on the day of the auction the vehicle did run (of a fashion) meaning a better price could be requested!
A basic inspection was carried out to assess wiring, connections, fuel quality, fault codes and some initial basic live data. This in itself revealed numerous faults that would link the sequence of events prior to the poor running condition.
The basic inspection confirmed fuel quality to be good, but engine bay and cabin wiring to have been modified, the alternator wiring to be severely corroded, and 2 x fault codes P0340 and P0335 along with the symptom start and stall. The live data revealed reasonable engine speed, good immobiliser data, a cranking signal set to ON (cranking or not), and no injection feedback values during brief engine run conditions! Given the engine would not run long enough to assess the charging system the fault codes had to be pursued remaining mindful of the recently modified engine wiring!
In September of 2014 we launched the next generation of Automotive PicoScopes with a host of exciting features. The new scopes are available as 2-channel 4225 and 4-channel 4425models, and are supported by a complete range of kits to allow a workshop to earn money from their PicoScope right out of the box.
One of the exciting features with our new PicoScope 4225 and 4425 scopes was Floating Inputs. The use of Maths Channel A-B perfectly demonstrates this new feature. Think back to a starter motor voltage-drop measurement using a voltmeter across the main supply cable. This would traditionally be carried out by placing the positive test lead to battery positive and the negative test lead to the starter motor terminal 30 (Main connection terminal). The starter motor would be energised and the value displayed on the voltmeter would read the voltage drop across the starter cable.
Using the PicoScope 4223 or 4423 each input shared a common ground. Connecting the ground cable of a test lead to battery negative (of any channel) would also ground the scope's remaining BNC sockets. This is fine for all measurements made with reference to ground (0 V) but the test in question has the ground lead connected to +12 V. To carry out this test using the PicoScope 4223 or 4423 scope we need to utilise 2 Channels. Channel A connected to battery Positive terminal, Channel B connected to terminal 30 of the starter motor and a test lead ground cable connected to the battery negative terminal. The engine is cranked and 2 voltage readings are taken at the battery and the starter motor. Using the Maths Channel (A-B) we can calculate the voltage drop.
Using the PicoScope 4225 or 4425 with floating ground inputs, we can carry out the volt drop test as with the voltmeter (using one channel only):
The term floating defines the architecture of each BNC socket.
Connecting the ground cable of our test lead to either battery negative or +12 V no longer connects the remaining BNC sockets to ground or +12 V. Each BNC socket can now be connected to a reference voltage of 30 V relative to chassis ground. In this scenario the scope reads the voltage drop during cranking without the need for a maths channel whilst utilising only one channel, so allowing your remaining channels to be used for additional measurements. For example, Channel A connected as per the voltmeter, whilst channel B could be connected to the crankshaft sensor measured with reference to ground (monitoring cranking speed).
In summary: Like a differential oscilloscope, each channel requires its own reference. The BNC outer of each channel must be connected to the system under test. Some PicoScope 4423 users are used to connecting just one probe ground clip regardless of the number of channels in use - this will not work with the new PicoScope 4425. As with any differential measurement system, where both input Hi and Low can be connected to a voltage above system ground, there is a limit to how far these inputs can sit above the system ground - the common mode range. The 4425 has a common mode range of +/-30 V at the scope inputs. This means that the voltage between the BNC terminals and the USB/digital backend cannot exceed +/-30 V.
Our Waveform Library feature in PicoScope 6 Automotive is growing at a superb rate, with over 1000 waveforms now available.
To access the Waveform Library you must have an automotive scope connected and have a valid user name and password for the Pico Automotive forum.
We recently ran a competition with Aftermarket Magazine which attracted 100s of entries! We are pleased to announce the winner is....
...Phil Leeks, of Town Garage, Leeds. Phil won a PicoScope 4225 for correctly answering "ConnectDetect" to our question "Which feature confirms the probe has made connection to the circuit under test?". You can see Tony Shortstaff showing off the company's new PicoScope in the picture here on behalf of Phil.
Steve Smith, Automotive Applications Specialist from Pico's Automotive Technical Support provides a tech tip on graphing RPM with a Maths Channel.
Did you know we can make use of the Maths Channels feature to calculate RPM (revolutions per minute)? This really does become invaluable when looking at subtle changes in engine speed applicable to very light misfires.
We have to create the Maths Channel formula to calculate the frequency of our engine speed signal relative to 1 revolution of the crankshaft and multiply by 60.
E.g. Our Crankshaft pick up ring has 36 teeth with 2 missing as TDC (top dead centre) reference. Whilst in reality we have 34 teeth, we must include the missing teeth in our formula for accurate RPM results. To explain further how the Maths Channel can display RPM we need to look at the theory.
We are looking at the frequency (measured in Hz [cycles per second]) but require revolutions per minute (RPM):
RPM = Frequency (Hz) x 60 (making our number now per minute [60 seconds in a minute])
So: 1 rotation of 36 Teeth of our crankshaft pick up is equal to: Hz x 60
The Maths Channel formula is written as follows: 60/36 * freq(A-2.5)
This enables the PicoScope to calculate RPM based upon the 36 teeth of the engine speed signal.
a. In the upper (Units) section type "Engine Speed" in the Long Name and "RPM" in the Short Name.
b. In the Range section it is best to enable Override automatic range selection. This allows manual override for the actual range you require (in the example I have selected 0 RPM to 1500 RPM).
c. Click Next and Finish.
d. Via the context menu (right-click of the mouse) enable your created Maths Channel and click OK.
Your new Maths Channel will appear and will plot the RPM of the channel you have requested (in our case A-2.5 is an RPM maths channel for Channel A).
Typical Maths Channel formulas for various engine speed configurations are:
RPM calculations using Maths Channels is not limited to a crankshaft sensor signal. Any stable signal output relative to 1 crankshaft revolution can be utilised. Exhaust gas pulsations of a 4 cylinder engine for example:
2 x exhaust gas pulsations per crankshaft revolution can be used to obtain RPM (Engine speed), in the formula:60/2*freq(A)
Go ahead and play with the Maths Channels feature as it will open up a whole new world of measuring techniques, revealing even more about your input signal.
Automechanika Shanghai, China
Automechanika Shanghai 2013 lived up to its status as the world's second largest international trade fair for automotive parts, accessories, equipment and services and the best platform for tapping into the Chinese and overseas markets. The 2014 show is expected to attract 4,800 exhibitors and 86,000 global buyers.
Hongke, our automotive distributor in China is attending the show to showcase many of our automotive products. Why not pay them a visit if you are attending the show? You will find them on stand W5A03.
9th - 10th December 2014
2345 Longyang Road,
Pudong New Area Shanghai P.R.C. 201204
Please visit Pico Exhibitions for the latest list of exhibitions and trade shows that Pico and its representatives will be attending.
Thanks to our continuing success and growth Pico are always seeking talented people to join our company.
Please visit http://pico.jobs/ to see our current vacancies. We look forward to hearing from you!
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