Vacuum waveform analogy and ID help
Posted to Technical Tips Forum on 6/25/2013
15 Replies
Here is something that seems to help me in understanding a
vacuum waveform. I'm not claiming to invent this and
actually didn't even bother searching much to see if this
same idea was posted before.
So far I really see this cranking vacuum waveform thing as
very useful. I thank my buddy Brian T. for making me revisit
the idea. Thanks also goes to the Brandon B at autonerdz for
this awesome idea for a $3.00 BLS I have come to love. This
is obviously done on a pico but if you have a sync probe for
your scope and buy an FLS or make the BLS you can do this
with any scope !
Most of you know the vacuum waveform is quite difficult to
master. At least it is for the simple minded techs such as
myself. The cylinder ID can be helped greatly with a WOT
overlay but is still a little cumbersome IMO. This way is
sort of crude but I think its down, dirty, and effective it
can just be jotted down on a piece of paper if needed.
Most everyone knows about companion cylinders and how to
find them right ? For those who don't its really simple take
the firing order and break it in half. This one 1342 put the
first two numbers 13 on top of the second set 42. So 1 and 4
are companions and 3 and 2 are companions. This means the
piston is in the same place as its companion . Knowing this
is huge in this simplification process. If we sync #1 to a
plug wire or coil we will have this easy to follow map.
1994 Plymouth Sundance Duster, Waveform
I you look at the sync probe in red on #1 wire the first
blue trace right under it is the companion cylinder #4
exhaust stroke. If you label the top humps the firing order
starting there you get 4213. Since you know that the vacuum
event happens right after the exhaust event the first dip in
the waveform has to be #4 intake stroke. So you label the
bottom 4213.
I don't know why this seems easier to me? Maybe if your
struggling with the vacuum waveform this may help you out
as-well. I didn't bother posting this in Autonerdz because
those guys are way beyond this. This is baby step stuff for
most of the guys there .Im quite intimidated there and I
feel like it would be more useful here. I really like
reading there just don't feel I have much to contribute. I
hope nobody has any hard feelings. I am only sharing
something I find really cool. If anyone has anything to add
please do.
Oh yeah # 3 exhaust follower fell out as that valve is stuck
slightly open.
I know this is an easy one and being a 4 cylinder makes it
nice with not so many events. The principal still applies to
V engines and it seems like cranking waveforms quickly rule
out a (major problem) quickly. The running really didn't
look much worse I just had to change the scaling a lot and
even added some filter.
Mike from Ohio
Files Referenced:
15 Replies Received
(View Replies)
15 Replies Received
(Hide Replies)
|