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Hey Guys.  I just wanted to start a discussion about diagnostics for the DIY'er or very small shop owner.  I'm curious to see what people are doing in this arena.  A driving force for most of my work has been, "Can I buy a tool and get enough use out of it to offset the costs involved, or possibly even be money ahead?  [Can I sell it to the wife?😉]  For DIY'ers the answer is usually YES!  A $3000 scan tool might be perfect for a full-time mechanic or shop owner, but can a DIY'er justify this cost?  Are there alternatives?

I was raised working on tractors and old-school engines.  As much as my old-school self has resisted, I have come to realize the way of the future is electronics.  I believe most engines/mechanical work is now about 30% mechanical (the stuff we're all good at) and 70% electronic (the stuff we better get better at).  I suspect there are a great many of us in the same boat.  I'll fill-in my story/situation as we go, but I suspect there are a bunch of guys out there who did a couple years of Auto-Tech in high school, who are a little bewildered at the modern day electronics.  I myself have had to fill in some of these gaps, which I'll get into.  Hopefully we can help each other!

If you have some unique or 'old-guy' ways of deciphering modern-day diagnostics, I'd love to hear your ideas!  I'll throw some of mine in there as well.

Modern diagnostics are dominated by proprietary and generic scan tools.  But I suppose the question boils down to...Are there DIY-friendly alternatives?

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  • Moses Ludel changed the title to Why Use an Automotive Oscilloscope for Diagnostics?
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Wayne...I am watching the response to your new topic.  Thanks much for posing these questions.  I have been exploring automotive oscilloscopes for some time and can say that there may be more to gain from an oscilloscope than the use of expensive, high end scan tools—especially scanners that require ongoing software subscription updates to match the latest OEM programming and new model changes.

One thing that strikes me, having over a half-century of automotive mechanical and electrical troubleshooting experience, is that OBD, OBD-II and CAN Bus made technician/mechanics dependent upon scan tools—until the advent of the wave form oscilloscopes.  While a scan tool can pry into the information stream and data within the ECU, ECM or PCM, an oscilloscope reads and diagnoses any device that can generate a voltage signal over a time interval.  This includes reading engine relative compression (measuring the amperage fluctuations at the starter motor while cranking) or the fuel pump's condition from the voltage/amperage draw and wave form of the fuel pump while the motor's commutator rotates.  

With an oscilloscope, the EFI electric fuel pump can be diagnosed while still in the fuel tank.  In fact, it can be diagnosed from the current flow at the fuel pump fuse or relay, without doing much more than lifting the hood and opening the fuse/relay box.  There are unlimited ways an oscilloscope can help us understand engine condition, electrical gremlins, valve and spark timing events, the list seems endless. 

Imagine not have to wait until the ECM, PCM or ECU software throws a trouble code for a fuel pump failure.  Before going on the Rubicon Trail or to the Moab Jeep Safari with your 4x4, you can test for signs that the in-tank fuel pump is either okay or ready to quit soon—long before the engine management computer or a scan tool has enough data to throw a Diagnostic Trouble Code (DTC).

Like all other tools, oscilloscope cost is the big consideration for DIY and small shop owners.  High end oscilloscopes like the Pico units have an excellent reputation and user-friendly software.  For the magazine's reader/viewer and forum members, however, I am concerned about your tossing $3000 at a scope.  Like Wayne suggests, if that is over budget, what purpose would it serve?  Instead, I just ordered an Autel MP408 automotive oscilloscope and the MSOAK Accessories Kit to see just what we can accomplish with equipment that retails for well under $1000

I got on this path when it seemed that our '99 XJ Cherokee and '05 Ram/Cummins truck required a Miller/SPX DRB-III scan tool for troubleshooting.  The DRB-III tool has been the FSM recommendation since the late nineties and through 2007.  The DRB-III tool sold new for as much as $6,000 then became obsolete at Chrysler/FCA dealerships when Mopar went to PC-based WiTech scanning and onboard computer re-flashing.  Today, a used DRB-III can cost $2500-$3000 at eBay.  There is an aftermarket DRB-III+ Emulator that some find useful, and it costs $2,890.50 (USD):


DRB 26.jpg

 High end OEM and aftermarket scan tools can be expensive and require periodic software updates.  This is a DRB-III scan tool on loan for a filming session years ago, provided by a colleague/friend at Miller/SPX (now Bosch Service Solutions).  Once an advanced technology dealership tool, these no longer supported scanners sell for $2500-$3000 in the used/eBay market.  Aside from PCM re-flashing, can we emulate or beat the functions of a DRB-III Tool with a $1000 oscilloscope package?  We shall see shortly!

Our other option is a contemporary high end aftermarket scan tool ($4000-$6000) with a $1500-$1800 per year software update requirement.  Like Wayne, my aim is to perform all service work at my shop, the reason I began looking for diagnostic tool alternatives.  Voila!  The automotive oscilloscopes popped up on the radar screen.  Several months ago, I plunged into every automotive oscilloscope training session and seminar I could muster.  At the 2020 AAPEX Virtual Event in early November 2020, I studied many hours of professional training webinars conducted by industry professionals like John Thornton.  I have studied every PicoScope and Autel oscilloscope video available at YouTube.  

In the interest of 4WD Mechanix Magazine and Forums readers and viewers, I decided to see how much diagnostic troubleshooting can be done without a high end scanner and expensive software subscriptions.  I have a decent trouble code reader/scanner that can catch real time fuel trim and  glean basic PCM data.  With the affordable Autel MS408BMC and MSOAK equipment, I can plunge into oscilloscope diagnostics.  My initial tests and observations will be shared at the magazine and forums.  Eventually, a series of how-to instruction videos will be produced for the magazine's Vimeo On Demand rental network. 

Along the way, I will compare traditional tools and diagnostics procedures.  Like Wayne notes, the goal is to illustrate the value a wave form oscilloscope can bring to engine, transmission, electrical and chassis diagnostics work.  Is this the ultimate in-depth troubleshooting tool?  Can we save thousands of dollars and do a better job than an expensive scan tool?  Do we need an automotive oscilloscope?  We'll find out.  The only additional equipment I can forsee would be a pressure transducer kit for performing in-cylinder, tailpipe and fuel system pressure testing.

My earliest concept and use of an automotive oscilloscope was the single channel engine analyzers of the sixties that I used as a light and medium duty truck mechanic.  I taught adult ed Automotive Techology in the early eighties with similar machines.  In the early nineties, I acquired a vintage Sun 720 Engine Analyzer that was later helpful (2005-2009) when we ran a mechanical restoration shop.  My Sun 720 engine oscilloscope worked perfectly for pre- and postwar classic cars, vintage Corvettes and breaker point ignition muscle cars.  I added a vintage Allen Distributor Strobe Machine to my testing and tuning equipment.  I still have the Sun 720.  Used properly, it can perform a range of engine tests.

Today's better wave form oscilloscopes are multi-channel.  The Autel MP408 has four channels.  This expands the scope's capability to include pattern overlays.  An example of how this works would be checking the relationship between the camshaft and crankshaft positions using two channels of the oscilloscope.  With the engine running, or even just cranking in the case of a no-start, the crankshaft and camshaft position sensors each send a voltage signal to the oscilloscope.  For a 2.5L or 4.0L Jeep engine, this can tell us whether the crankshaft and camshaft are in alignment or not. The number of degrees of separation can indicate a misaligned, loose or jumped timing chain!

I encourage serious DIY-ers and small shop owners to follow up on Wayne's invitation.  Jump into this discussion!  As I share oscilloscope uses at the magazine and forums, your feedback and questions would be valuable and helpful.  Please share your experiences with scopes and scan tools!

Thanks for opening this topic, Wayne.  We're in the 21st Century and need to step up our diagnostics and troubleshooting game!  Pinpoint troubleshooting can save time, needless parts replacing and bad guesses.  Let's see where the automotive oscilloscope fits into that equation. 


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