Pinpointing an engine mechanical-fault within minutes
Posted to Technical Discussion Forum on 9/20/2014
49 Replies
iATN'ers,
Ok...I was presented yesterday with a 2013 HONDA CIVIC Si
(2.4L). The vehicle was towed in due to a
"stall/crank,no-start". We had a heck of a time getting it
started but when we did, it would barely rev and missed
terribly. Codes were cleared and none presented in the short
time we had it running. I will note that during cranking the
cadence exhibited sounds of at least one dead-hole.
Up until yesterday I have experimented heavily with
pressure/vacuum testing to supplement after wards, what I
have proven otherwise with more traditional-testing. I do
this so that I may safely learn by starting with a
conclusive answer and working backwards to make the
correlations. Im pretty excited about this case-study
because, as you will see, Ive proved to myself that I have
indeed learned from "practice, practice, practice" and can
rely on these advanced tests to yield me conclusive-info
without the more invasive/traditional tests (no more
"training-wheels").
I began my testing with a 2-trace scope capture of
RELATIVE-COMPRESSION and a #1 IC-COMMAND. My waveform
displayed a lack of compression on cyl #4 only. I then added
the FLS to the mix and attached it to the brake-booster port
in the Intake-manifold. [2013 Honda Civic Si,
Engine/Propulsion Waveform]
[2013 Honda Civic Si, Engine/Propulsion Waveform]
If you refer to the captures, you can clearly see the
problem. With these two captures alone (approx 10min of my
invested time) and an overlay, I could conclusively tell not
only that cylinder #4 was leaking but the intake valve
wasn't sealing properly. More-Importantly, justified the
need to tear the top of the engine apart for further
inspection. (Take my word for it...the configuration of the
engine requires removal of the cowl panel just to remove the
COPs and Valve-Cover.) Upon removal, the evidence was clear
(refer to the attached).
[2013 Honda Civic Si, Engine/Propulsion Photo]
#4 intake rocker-assembly has failed/fell apart. A "C-clip"
that holds the assembly together became dislodged. This
allowed the pivot pin to move longitudinally and jam itself
against the cam-holder, holding one of the #4 intake valves
off its seat ever so slightly. [2013 Honda Civic Si,
Engine/Propulsion Photo] [2013 Honda Civic Si,
Engine/Propulsion Photo]
With the Rocker-Bridge assembly and both camshafts removed
from the cylinder head, confirmation of the #4 intake
valve's integrity was confirmed. It sustained no damage.
Replacement of the #4 intake rocker-assembly was the only
new component fitted to the engine and upon assembly, roared
to life and didn't miss a beat!
This was the perfect opportunity to prove that learning this
form of testing can save you boatloads of time and
pocket-fulls of money. Please let me know what you think of
the captures above and feel free to be critical...Im always
looking to improve my delivery. (sorry about the photos...as
you can see, I still need some practice with my
presentation..VBG )....GET BACK TO ME WHEN YOU CAN! THANKS
FELLAS!
TAKE CARE, -BRANDON-
Brandon from Indiana
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