Just before we get involved in using the actual oscilloscope for this series of tests
I'd like to take a very simplistic step back in mechanical assessment
and this means using the PicoDiagnostics platform for the compression test.
Now you must appreciate this is a relative compression test, it's a
theoretical compression test, where an analysis is based on all of the other
balance of compression against the cylinders, it's not actually a
compression test in actual terms. To make it interesting I'm going to use a valve
which allows me to bleed off some pressure so we're going to get, in effect,
a poor value on one of the cylinders so we can do some some meaningful analysis
So, let's set that particular part of the test up. I've already partly prepared the vehicle,
I've taken out the spark plug, I've just chosen cylinder 1 it's irrelevant for
this particular demonstration, which cylinder we are going to put the fault on,
but basically I'm allowing a bleed of pressure from that cylinder to produce
poor compression that's the the idea
as you can see I've estimated a leakage
and because this is a compression test based on, we're not using that just yet,
based on the evaluation of voltage differential across the battery
potential difference, whereby during compression that will increase the
voltage drop, work done by the starter motor will increase the amount of
voltage drop during compression. So, theoretically, I've introduced a fault on
cylinder 1, we have a channel 1 the blue channel connected across the battery we
need to exit the Pico oscilloscope software and engage the Diagnostics
platform, select the compression test, it's already default to 4 cylinders
which this vehicle is and we are ready to conduct the test so I'll go around to
the vehicle which is now ready, we have got battery support on as well, you
may have noticed that already, just to keep the voltage on the battery at a
healthy level that doesn't affect the accuracy of this test so I'm going to
conduct the clunking test and you can view the results
So I think we've got a very definitive conclusion here and this is
actually an extremely accurate and satisfying test for me because the
engine isn't running, we're not interested in ignition,
we're not interested in fueling, we're interested in the third dimension.
When dealing with an anomaly with combustion, and I use those words very carefully,
there are three causes: ignition, fueling or mechanical, the fact this engine isn't
running this test does prove conclusively there is a mechanical
internal condition with that result and I'm fairly satisfied with that at this
level but a student on one of my courses recently said Frank how does it achieve
this result well it does it from voltage drop so I'd like to change this test and
go back to the scope and show another means of doing this test that doesn't
produce a bar graph but actually does look at voltage and current flow through
the battery during this test so I'd like us now to set this next part of the test
off technique a couple of minutes to do so off-camera and then we're going to go
back to scope and do the same test, a non-start crank test and actually prove
we're looking for a 79 percent deficiency or else you could say, we're looking
for around a 30% deficiency against the other cylinders but measuring it perhaps
differently looking at current and voltage