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\viewkind4\uc1\pard\f0\fs20 Compression Transducer Signal Analysis...\par
\par The Comp-Peek automotive compression transducer
is a dynamic compression sensor developed for the Auto Scope 1, but can also be used
with your own Scope.
Why for the Auto Scope 1?
Well, the Scope 1 has a special software algorithm called "Signalator", which is an automated
fault recognition feature.
It'll record, capture, analyze and point the issue to you without any intervention on your
part.
So, we needed a special set of specifications baseline to work with Signalator.
Other than that, the Comp Peek Probe will perform what it was meant to do on your own
scope, minus the Signalator automatic fault capture of course.\par
Why you need the Compression Transducer...\par \par
Using the good old compression gauge is fine; there's nothing wrong with it.
However, a compression gauge gives you a maximum reading, not the running minute compression
signature that this compression transducer does.
This sensor peeks into the engine in a very deep way.
With it, you can determine, intake and exhaust valve opening, valve seal, weak springs, and
virtually anything related to the valve train.
How hard is it to read the signal?
It takes a bit of practice, but the compression peek transducer probe comes with it's own
easy to read manual and oscilloscope software.
Within a few days you'll get the hang of it.
Next, will show you how to read the compression signal waveform.
\par \par
Reading and Analyzing a Compression Waveform...\par \par
I will start this videos with one caveat, it is the relationship of the compression
waveform data-points that matters, not so much each of the specific value alone.\par
\par Modern automotive diagnostics, and the advancements
in electronics, has unleashed various automotive technologies in the field of diagnostics.
The compression or high pressure probe is one of them.
We at Automotive Diagnostics and Publishing created the Vac-Peek and Comp Peek Probe.
In this video, we'll concentrate on the Comp-Peek Probe signal analysis.\par
\par Here is a typical compression waveform at
idle taken with the Comp-Peek-Probe.
You might ask yourself, are these compression signal waveforms the same for all cars?
The answer is, yes, as long as they're four cycle engines.
And as far as we all know, all automotive engines are 4 cycle engines.\par
\par The second figure, shows the same waveform
using the included Comp-Peek-Probe Oscilloscope, without Signalator.
Although not the Scope-1, it is a very capable scope software and comes included with the
Comp Peek Probe Scope kit.
\par \par
With the Comp-Peek-Probe, the engine can be checked for camshaft to crankshaft timing
problems, electronic variable camshaft timing issues, intake and exhaust valve sealing faults,
valve spring, piston ring seals, worn cam lobes, restricted exhaust, ignition timing,
and cylinder misfire issues.
\par \par
We'll begin, by analyzing the anatomy of an engine compression waveform at idle.
At higher RPMs things get weird due to the higher engine speeds, and the usability of
the signal goes way down.
So, without further ado, here's analyzing a compression waveform.\par
\par Facts About Analyzing Compression Waveforms\par
\par We'll start by dividing the compression signal
waveform, into four separate sections.
The divisions happen at 180 degrees of crankshaft rotation.
So, the crankshaft rotates halfway, that's 180 degrees.
If it rotates one complete revolution, then it's 360 degrees, basic geometry.
Now, the camshaft rotates at half the rate of the crankshaft.
So with that in mind, we can ascertain that the crankshaft rotates twice, for every camshaft
rotation.
That is basic four cycle internal combustion engine geometry.
As I've mentioned, we'll divide the waveform into 180 degree intervals, as seen next.\par
\par Now these division lines also correspond to
the 4 cycles on the internal combustion engine.
The cycles are:\par \par
Power or Detonation\par \par
Exhaust\par \par
Intake\par \par
Compression\par \par
The first line corresponds to the peak-compression point, right before the spark, which causes
the mixture to detonate or explode.\par \par
This is the point you use to determine if you have proper compression.
It is not a, \ldblquote How much compression in PSI we have\rdblquote . Some software will
output a calculated compression number value, but that's the wrong approach and is misleading.
What's important is the ratio, or the relationship of this line along the waveform to the other
measured points.
In other words, how does this key point compares to the other measurable key points, as explained
next.\par \par
In real life, you can expect a value of around 60 PSI for most engines.
That's because there's a huge different between static compression, or what you see using
a compression gauge, and the dynamic compression, using a transducer or Comp-Peek-Probe.
The dynamic reading is way more exacting, and shows you real life values on the fly.
The static way is fine as a generalized idea, but often times misleading by itself.
Static compression reading will also not reveal lesser valve leaks, and various mechanical
issues, due to its averaging nature.
Also, the gauge is not too sharp to begin with.\par
\par Here we can see the easily identifiable 4
cycles, as they correspond to the compression waveform.
Remember that all the signal waveform specifics, have all to do with the travel of the piston,
and its relationship to the valve-train.\par \par
As you can see the next point of interest is the detonation, or power down-curve of
the waveform.
In this case, we're taking the reading with the engine at idle, and the particular cylinder
disabled, so the spark-plug has been removed, and the one ignition coil disabled somehow.\par
\par So, what we actually see here is a pressure
signal curve, not necessarily the mixture exploding.
But the compression reading seen here is a mirror image of a working cylinder.
A downward curve, seen next is expected, and it points to the general health of the exhaust
system.
If you had a clogged-catalytic converter, you'll see it here.
The bottom of this curve, right before the second 180 degree line, has to reach its bottom
most point, as seen before the upward going pressure hump started.
That low point signifies proper exhaust.\par \par
Then, comes the second section of the waveform, the exhaust section.
It is described as a flat top hill.
Ideally, this section should rise to about 1/6th to 1/9th of the peak compression spike.
This is the cylinder in the exhaust cycle.
Issues associated with this section of the waveform are clogged catalytic converter,
and exhaust valves not opening completely, maybe due to a variable valve timing issue.\par
\par \par
Next, Is the intake part of the compression waveform.
The intake part of the waveform is denoted by a quick downsloping, followed by a flat
line.
The downsloping section points to the remnants of exhaust gases, leaving the combustion chamber,
and then a specific amount of vacuum created due to the downward moving piston.
This is also important, and will vary a bit depending on whether you goose the throttle
or not, during the compression test.
In general, this section will tell you if you have good vacuum created at the cylinder.
As a general rule, this section should be as low as possible on the scope.
This should be the lowermost spot on the wave.
It should match the exhaust valve open event, if all is well.
Restrictions at the intake throttle body butterfly plate, severely clogged air filter, turbo-waste
issues, variable intake valve control system, or anything else that will affect the air
intake will raise this line.\par \par
As I've explained before, it is the relationship of the compression waveform data-points that
matters, not so much each of the specific values alone.
How one section of the waveform looks is worthy of notice, but how all the waveform data points
or event relate to each other is king.\par \par
Finally, there's the compression section.
This section is categorized by an upward sloping raise of the pressure content in the cylinder.
It is then finalized at the uppermost point in the complete waveform, and proceeded by
the combustion power cycle.\par \par
The compression section has to be at least 8 to 9 times the height of the exhaust signal
level.
Here's where you know or determine piston and valve train seals, how well the cylinder
can contribute and hold pressure, and is a precise indicator of engine health.
Issues with variable valve timing will also cause the compression section's highest-most
spot to be low.
Remember that the Comp-Peek-Probe tests are dynamic, meaning as they happen, and for that
matter are stressed tests.
You're not just doing a static test with a gauge.
You're really seeing what the engine is doing mechanically, as it is doing it, on the fly,
in real time.
There's no substitute for this level of insights.\par \par
\par \par
\par }
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