More Than One Way Find That Misfire
Posted to Technical Theory Forum on 9/29/2014
32 Replies
Good Evening Fellas (and Ladies)..
Last-week, I was presented with a 2001 ACURA INTEGRA DOHC
1.8L (B18C1) exhibiting an intermittent misfire. The
customer told me, the misfire is more noticeable during a
steady-state cruise/70mph, although I can feel the misfire
right in the workshop, but very infrequently. Surprisingly,
"snap-throttle/brake-torquing" could not flush-out an
ignition-misfire so out came the FLS/lab scope.
The 2 traces revealed a misfire intermittently occurring on
cylinder #4, as seen in this trace.
[2001 Acura Integra GS-R, Engine/Propulsion Waveform]
I switched to an ignition-scope because it was the next
logical/easy general-test to help guide me down a
diagnostic-path. A "paraded" acquisition quickly revealed
some secondary-leakage on #4.
[2001 Acura Integra GS-R, Ignition Waveform]
So an inspection of the "fairly-new" ignition cable was
conducted. Nothing stood-out as a potential leak-point for a
spark-deviation so the plug was removed as well.
The #4 spark plug was fairly oil-fouled. As a result, the
porcelain insulator had cracked and allowed the spark to
short intermittently (very-surprising, given the excess
KV-DEMAND of the snap-throttle/ brake-torquing couldn't
reveal the problem initially...his complaint was at a
steady-cruise!!!). I was informed by the owner that he was
aware of the oil-consumption and he planned to have the
valve-guide seals replaced soon. A new set of plugs was
fitted and the vehicle ran flawlessly. The car was returned
to the owner and he experienced no more issues....for
2-weeks...
The vehicle returned today with a more steady-misfire at
idle, although not as bad at higher RPM. A vacuum gauge
revealed a slightly bouncing-needle. Again, the
ignition-patterns were analyzed and #4 revealed an issue,
however nothing like it did before! The ignition pattern
appeared to have a very turbulent burn-line and when
paraded, #4 Firing voltage was far-less amplitude then the
remaining cylinders.....ugh-ohh.....this feels as though we
are heading towards a mechanical-issue!( see the
ignition-patterns below)
[2001 Acura Integra GS-R, Ignition Waveform] [2001
Acura Integra GS-R, Ignition Waveform] [2001 Acura
Integra GS-R, Ignition Waveform]
I interfaced the vehicle, first with : *CH1(YELLOW)- #1
IGNITION-SYNC *CH2(GREEN)- FLS ON THE INTAKE MANIFOLD
*CH3-(BLUE)- RELATIVE-COMPRESSION The engine was cranked and
the info was captured. The waveforms were exhibiting an
obvious compression-loss on cylinder #4. There was
definitely a disturbance evident in the intake-trace. Rather
than analyze the capture, I chose to simply move the FLS
from the intake-manifold to the tailpipe. A very-evident
issue was present in the exhaust stream as well. I uploaded
the waveforms to PC so I could apply an overlay and begin to
put all of the puzzle pieces together. ...SEE THE ATTACHED
BELOW!
[2001 Acura Integra GS-R, Engine/Propulsion Waveform]
[2001 Acura Integra GS-R, Engine/Propulsion Waveform]
There is definitely more than one way to skin a cat. Ive
learned this from Greats like Albin Moore...As he says, he
is always looking to put "THREE ARROWS IN THE TARGET". I
realize that the diagnostic-path I chose with this vehicle
was not necessary to draw a conclusion but I more-so wanted
to demonstrate multiple-tests that backed-up my data to help
me put the diagnostic-puzzle together. The more I use what I
have learned from others in regards to
ignition/pressure/vacuum-waveform testing, I can feel myself
becoming more confident in my diagnosis'. The connection
between the results of my testing and engine-dynamics is
also far less of a gap. With a bit more practice, I can see
these techniques becoming replacements for the more
traditional testing that has served me well for years. As
always I welcome all questions/comments/criticism...every
opportunity for anyone to learn is what Im trying to
generate with my posts...Thanks Fellas! -BRANDON-
Brandon from Indiana
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