Posted to Technical Theory Forum on 3/20/2013
28 Replies
[exhaust pulse waveform]
Back in the old days when I was in charge of the Tech Center
at Allen Test Products, we did a lot of things to make the
engine fail in order to collect data. I had a budget to hire
Automotive students of Western Michigan University to
assist, and we had a ball. Besides measuring Torque and HP
on the dynamometer, we could measure fuel consumption. One
of the test we did was to determine the effect of one
cylinder misfire and found a 30 % waste in energy. This was
before OBD-2
[6 cylinder - No misfire]
Ironically we can proof the same without all that equipment
by looking at the pulse waveform of the exhaust. [66548]
Here is an illustration of all the 6 cylinders normally
firing after the fix. [66547] This illustration shows the
misfire, where we can see the repeat of all cylinders. The
condition is 850 RPM in drive. Notice that the misfire
caused a stumble but it took all the 5 contributing
cylinders to restore to normal, and the cycle starts all
over again.
This is extremely valuable when you can print the evidence
out (on your letterhead of course) and the owner shows
everyone at the water cooler. It is a silent promotion of
your shops expertise. The point is: that it is not the loss
of one contributing cylinder, but it is affecting all
contributors. When driving at 60 MPH it takes a little
deeper foot peddle and a more fuel to maintain the desired
road speed.
Prolonged driving with a bad plug wire or dripping injector
or any absence of a spark can have nasty consequences..
Misfire can damage a converter very quickly, especially the
manifold mounted or "close coupled" converter. Unburned
fuel, high temperatures and literal flame introduced to the
ceramic can actually crack the brick causing a blockage and
melt-down
Mac from Michigan
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