Author Topic: oscilloscope for automotive troubleshooting  (Read 17609 times)

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Offline NiHaoMike

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oscilloscope for automotive troubleshooting
« on: June 30, 2010, 10:10:59 pm »
I was deciding whether to get a new Rigol DS1052E or a used analog oscilloscope. Initially, I was looking at just for general electronics use. But recently, my car (2002 Ford Taurus) started having some misfires. (I replaced the spark plugs, which improved but did not completely fix the problem. Ford = Fix Or Repair Daily...)

So what should I look for in an oscilloscope for automotive use? I have seen pictures of a mechanic working on a state-of-the-art Toyota Prius with just a 15MHz analog oscilloscope, so the 50MHz bandwidth of the Rigol should be enough for almost anything in automotive, right? Would I need a high voltage probe to scope the ignition secondary or would probing the primary be enough?

One main advantage I see with a digital oscilloscope is portability. Apart from that, would an analog oscilloscope with memory work as well as a digital? (The only analog oscilloscope with memory I have seen is an old Tektronix 7134, which is probably too big for automotive use.)
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alm

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Re: oscilloscope for automotive troubleshooting
« Reply #1 on: June 30, 2010, 10:54:33 pm »
Can't help with any automotive-specific questions, don't have any experience in that area. I do know that the Tektronix P6015(A) (HV probe, 50MHz 20kV or so, but not both at the same time) is popular with guys doing ignition work, but that's probably more for development that troubleshooting, I wouldn't expect your average mechanic to use a scope, probably dedicated tools that are easier to use.

I wouldn't go into analog storage scopes, this was a neat solution when digital storage was not feasible, but the storage CRT tends to die sooner, and digital storage is basically superior (which is not so clear cut when doing non-storage work). If you need storage, get a DSO, but you may not need storage. An analog scope is definitely larger and heavier because of its CRT. I've heard a story of someone embarrassing a Fluke rep when the expensive Fluke digital Scopemeter didn't show something in an automotive-related waveform that an old analog scope did show, but don't know specifics.
 

Offline bbarry

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Re: oscilloscope for automotive troubleshooting
« Reply #2 on: July 01, 2010, 12:22:09 am »
I use a Fluke 97 auto for my trouble shooting. The can be found on fleebay pretty cheap.
Still seems to have enough horsepower even on the newer cars. I also have the Ferret 950 KV adapter to go with it for viewing spark train and several amp clamps for trouble shooting injectors, fuel pump, ext.
 

Offline NiHaoMike

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Re: oscilloscope for automotive troubleshooting
« Reply #3 on: July 01, 2010, 02:54:31 am »
The Fluke 97 only has a sampling rate of 25MHz, or a single shot bandwidth of only 2.5MHz. That's too low for general electronics work.

There seems to be plenty of places to use an oscilloscope in automotive. Especially when dealing with strange problems that a ScanGauge alone cannot find.
http://www.picoauto.com/automotive-library.html
http://www.tiepie.com/uk/automotive/
It seems like a current probe is more important than a high voltage probe for general automotive. I have a Hall effect current probe that I built, but it's for use with a multimeter. The Hall element (Allegro A1321) is rated for a bandwidth of 30kHz, which is probably adequate for DC circuits since bypass capacitors would shunt much of the ripple at high frequencies. (I'll have to use a Rogowski coil for higher frequencies.)

http://www.picoauto.com/waveforms/Ignition/Primary/wave63.html
It looks like a high voltage probe is not necessary since the secondary voltage is reflected back onto the primary (just like in theory), but that assumes a good transformer. Is it likely for a fault in the transformer itself to not show up on the primary waveform? (On a side note, for whatever reason, Ford put all three flyback transformers in one module and then put it behind the intake manifold! Why they couldn't put it on the valve cover next to the front three plugs is beyond me...)
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Offline chscholz

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Re: oscilloscope for automotive troubleshooting
« Reply #4 on: July 01, 2010, 03:18:13 am »
Nihao Mike,

Obviously it depends a lot on what you need to do. I think a good starting point would be to figure out what bus your 2002 Ford uses.

If money is no consideration you would probably get a Vehicular Bus Analyzers (aka. VBAs) that can decode and trigger various flavors of LIN, CAN and FLEXRAY. You also find various flavors of MOST bus that feeds in-car entertainment systems. As far as I know the slowest CAN bus runs at 10 kbps, MOST goes up to 150 Mbps.

A quick Google search shows that at least one version of the Toyota Prius uses MOST50 (i.e. 50 Mbps) for the entertainment bus.

Chris
 

Offline charliex

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Re: oscilloscope for automotive troubleshooting
« Reply #5 on: July 01, 2010, 02:40:15 pm »
the picoscope is a very popular automotive scope, i don't care for it myself but people buy it because its popular and has some automotive specific software that help those that aren't scope savy, you can find a large community that uses it with lots of tutorial videos, so thats the benefit there, however it does apply to other scopes. Picoscope also sell a kit that shows you the most common probes and parts you'll need for automotive.

I mostly use inductive pickups and sharp long needle type probes for getting access to sensors.

I use a TDS2024B for all my automotive work, never been anything i've run into that it can't deal with. I would go for a minimum of a 4 channel scope though. the black and white 4 channel TDS is also more than enough, we use one of those in the shop for diagnostic work.

scopes are quite common for mechanics to have nowadays.

A CAN/LIN bus analyser is probably not that useful, since all they do is show you the data stream, not what it means. Most CAN bus stuff you'd actually use for engine diagnostic work is 512kbps and 1mbps and they're OEM specific anyway.

 

Offline charliex

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Re: oscilloscope for automotive troubleshooting
« Reply #6 on: July 01, 2010, 04:49:01 pm »
This is where i pickup my needle/piercing probes for probing sensors etc.

http://www.aeswave.com/
 

Offline NiHaoMike

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Re: oscilloscope for automotive troubleshooting
« Reply #7 on: July 01, 2010, 05:00:33 pm »
http://www.picoauto.com/secondary-ignition-pickup.html
http://www.picoauto.com/coil-on-plug.html
It looks like automotive high voltage probes do not actually contact the high voltage but instead sense electric fields. Such a probe should be easy to DIY, just a curved metal plate connected to a piece of coax with an overvoltage protector.
http://www.picoauto.com/mixmaster.html
That device sounds a lot like circuit I read about that turns a single channel oscilloscope into as many as 8 channels, but with reduced bandwidth.

It looks like the Rigol is still the best value for a new oscilloscope.
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Offline A-sic Enginerd

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Re: oscilloscope for automotive troubleshooting
« Reply #8 on: July 02, 2010, 07:14:34 pm »
I'm a gearhead myself first, engineer second.

I've never had need of an o-scope when wrenching. 2 of the vehicles I own are newer (a '99 Volvo, and '01 Toy), but admittedly have had to do limited repairs on the Toy (actually no repairs, just maint.). With the Volvo I've either known what it was right away (like when its coil went.....one of 5 ugh), or it's been just read the codes, do a little homework, and I have an answer. But maybe that's just me and a lifetime of wrenching (30+ years) has helped more than I realize.

Footnote: I have found that on the Volvo, a decent code reader has paid for itself many times over (think I paid like 150 bucks for it). Just don't always take the codes at face value.
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