Pressure Transducer Waveforms
Posted to Technical Tips Forum on 10/7/2009
41 Replies
1996 Chevy S-10 2.2 Liter engine. Customer says he requires
a new engine. He said he heard a knocking noise and
eventually it got to the point it will not start. He asks me
to either install a used Engine or get this engine running
so he can trade it in.
So I have the vehicle towed in and get in the vehicle and
crank it over.Its turning over real quick and sounds like
there is no compression.(The kind of sound you hear when
your cranking over an engine with a timing belt failure)A
quick note* on the scanner a code showed up for knock
sensor. I get out of the vehicle and I can smell the fresh
scent of raw fuel in the air,a visual showed no signs of
rods hanging out the side of the block or pan. I decide its
time to check some basics with the scope and a pressure
transducer, I remove the spark plug on cylinder #1 and I can
see the gap is about twice the size of what it should be.
I install a 500 PSI snap-on pressure transducer into
cylinder #1 and I hook up a secondary lead from the scope
and test leads to cam and crank sensors. I crank the vehicle
over and this is the waveforms patterns I get.[1996
Chevrolet S10, Engine/Propulsion waveform] We can see from
that pattern we have secondary ignition firing, a cam and
crank signal (out of sync compared to [1996 Chevrolet
Cavalier, CKP Sensor, CMP Sensor Waveform] ) and a
pressure transducer waveform that has an unrecognizable
signature pattern. With the fact its obviously out of time,
I then decide to remove the valve cover and loosen off each
rocker and examine the valves with my borescope (no valves
appear to be bent from what I could see with the borescope)I
decide I should do a leak down test anyways to verify no
valves were bent.(This test indicted a minimal leak down
rate on all cylinder) "So good no valves are bent" I then
decide its time to remove the timing chain cover and this is
what I see [1996 Chevrolet S10, Engine/Propulsion
photo]. Wow approx 9 teeth out. I install a new timing
chain and tensioner/oil change and button the front cover
back up. I then take another capture of this vehicle
cranking over [1996 Chevrolet S10, Engine/Propulsion
waveform] Well that looks better its now in sync.Now lets
see if this thing starts [1996 Chevrolet S10,
Engine/Propulsion waveform]Hey its running. Now since I
havent buttoned up the valve cover yet I decide to take some
running compression transducer waveforms with different
scenario's, I loosen off different rocker combinations and
capture the corresponding waveforms [1996 Chevrolet S10,
Engine/Propulsion waveform] Some interesting patterns and
pressure's displayed. I then check each cylinder separately
and note the captures [1996 Chevrolet S10,
Engine/Propulsion waveform] and a closer look at cylinder
#1 [1996 Chevrolet S10, Engine/Propulsion waveform] I
finish putting it all back together,installed new spark
plugs cleared the code and started it up running on all 4
cylinders, It ran very nicely [1996 Chevrolet S10,
Ignition scandata] And the Happy customer was very
surprised he didnt need an engine.
A little note, when using the 500 PSI snap-on Pressure
transducers they will give you a fairly good representation
of the running/cranking compression waveform pattern itself,
However the pressure Scale will be off to some duration
because of the inability to maintain the proper scaling.
When examining the running pressure waveforms with a good
sealing engine generally you should note where the exhaust
pattern peaks and this should theoretically cross over the 0
PSI line to confirm the exhaust is actually escaping the
engine as shown here [2002 Ford Focus,
ECM/Inputs/Outputs waveform]
Hopefully this helps somefolks out.
Kevin from Manitoba
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