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In past random browsing of the 928 forum here on Rennlist, I saw passing mention from dr bob of using an oscilloscope for testing the ignition on a 928.
This has piqued my curiousity, as I have two O-scopes. I want details.
Nothing is wrong, the Red Witch ran fine. However, this is for giggles and future reference.
I have a GoldStar OS-9020P benchtop 2 channel oscilloscope and a SEARS/Craftsman 161.21056 Automotive Diagnostic Oscilloscope.
I believe the Craftsman scope will be more appropriate. Mainly because I have used it to view the ignition patterns on the crate motor in my S-10. And because I am not sure how to hook up the GoldStar to read automotive ignition.
When I last used the Craftsman, two of the modes it would read in are single cylinder or batch kV. You could put the inductive pickup on a single plug wire and view its pattern, or connect the pickup to the coil and see the firing of all the spark plugs.
Because the Red Witch has two separage ignition systems, I believe single cylinder mode will be most useful. I could read and compare each bank against each other, though...
So, please chime in with your real world experience of testing the ignition on a 928 with an oscilloscope. Looking for you, dr bob...!
I have done a quick search here, but did not come up with much.
Are you referring to Group 28 in manual 1A of the WSM? I saw it had some scope testing for the 1984 Euro twin distributor, but nothing on the 85-86 EZF.
Is there a specific EZF Ignition manual that I have not yet found?
I made some simple wire-wrap inductive pickups, four turns close wound counterclockwise from source end, and connect a standard scope probe to each one. One on each coil wire, one on each distributor from a known cylinder plug wire. The plug wire pickup is the sync signal, coil wires are tested for all the patterns from that distributor. If you have two channels plus a separate sync input, sync on #1, one channel to each coil wire, and you can watch all eight cylinders at the same time.
Make all the pickup transformers exactly the same, and you'll be able to compare amplitude as plug voltage.
Both scopes can provide lots of entertainment- dr bob has a good setup for your GoldStar, and the WSM gives waveforms for lots of stuff: secondary ignition, injector pulse timing, CPS, etc. O2 sensor is another you can play with. Run into issues, dr bob is the go to guy. And post any stuff you think might be useful! For some typical waveforms I think you can download the manual for one of the USB scopes like Hantek, and there are some YouTube videos also.
For those playing along at home, the 'scopes we are using are cave-man technology. There are now some pretty nifty many-channel digital storage scopes that are signal-processing front ends that connect to your PC and software via USB, so you have a big laptop display to look at. Compare with a 4" round or -maybe- rectangular CRT display in the old-school tools.
Lots of common maladies in injection and ignition can be displayed graphically on the display, from sensor inputs from CPS, ABS, Hall sensors and speedo pulse senders, through injection and ignition signals and more. The [edit: ignition] display described above lets you verify that the firing voltages for all the cylinders are consistent and not too high. You can easily spot a fouled or disconnected spark plug, an ignition wire failing open, or the same wire with a spark leak to ground. Injection control inputs, switch actions, sensor signals, injector pulses, all help you find time-based and dynamic values that help you research problems you might be having.
It could be the same stuff as the WSM since the late Euros were also EZF and LH, but there is a file in the "fuel injection" folder on disc 2 called "'85 Test Plan EZF and LH" that you're looking for.
I must have been feeling the force last night before reading this thread, when I randomly scoped out different 'scopes on the 'net. I don't have an immediate need, but thought everything must be different than what I used in the 1970's.
What I'd more frequently want is the modern equivalent of a strip chart recorder (but without the ink run-outs). Yes, I know - a USB data logger.
I have used this program to TS a faulty FI pulse issues a few years back, turned out that the Square wave was being turned into a saw tooth by the Kick-down relay and killing the FI at random
I just installed it on Windows 10 and it seams to be working but would need to connect up my Voltage divider and probes to actually test it using an actual input.
I never tried this on an Ignition wire though, not sure if it would fry anything
Your "automotive" o'scope undoubtedly has inductive pickups, and a bunch of native functions and display overlays that are a great place to start. I used some 14ga solid copper house wire for mine, but no need to jury-rig stuff like this when you have a set already made up for the Craftsman o'scope. I've been casually harvesting inductive pickups from old timing lights, but don't have any two that match well enough to read both coils/distributors at the same time. Hence the hand-wrapped inductive pickups.
dr bob, HF sells a really cheep >10 buck timing light with inductive pickups, I've been using one to diag basic Ignition failures.
Maybe time for me to buy another one, great idea using old ones, thanks!
12-20-2016, 07:25 PM
Using an oscilloscope for 928 ignition testing...
