intermittent misfire at idle
Posted to Technical Discussion Forum on 11/1/2013
31 Replies
Good day all!!!
I had some fun yesterday making some correlations for myself
and proving-out some theories. I had the referenced-vehicle
above come in to the shop with the complaint of a
"rough-idle". The complaint was easily exhibited. The
vehicle did indeed exhibit a misfire at idle. if the RPM was
elevated even slightly, the misfire vanished. The vehicle
did not exhibit the symptom nor any others at all, under any
other driving-condition. I scanned the vehicle for
DTCs...P0300 was the only DTC flagged. I referred to
misfire-data and #2 was counting-up as well as #3. FREEZE
DATA registered the same operating conditions. Fuel Trims
were close to 1.0 off-idle but were as such during the
idle/misfire:
LTFT#1= .93 (cyls 1-2-3) LTFT#2= .98 (cyls 4-5-6)
This vehicle had 150k miles on it and didn't appear to be
properly-maintained. I had a strong hunch I was facing a
valve-overlap issue. I thought it would be wise to take some
BEFORE/AFTER captures using the First-look Sensor. I was
hoping to see something on it. I connected to the intake
manifold at the booster-port and referenced #4 coil-command
because it was very easy to access.
[2005 Honda Pilot EX, Engine/Propulsion Waveform]
I removed the valve-covers to attain my measurements...I
realized that the FLS was very capable of capturing
slight-changes but I learned something today as well....if
you refer to the actual-clearances on the right-side of the
capture, you will see that the further the clearances
deviate from spec, the more noticeable it is in the
intake-waveform. I found that pretty interesting, myself.
Below is the same waveform after adjusting the valves to
proper tolerances.
[2005 Honda Pilot EX, Engine/Propulsion Waveform]
Im curious if anyone is familiar-enough with the ATS
"H2O-sensor to explain to me how it would display the same
waveform by comparison?....better-yet, does anyone have any
of those waveforms that they would like to share so that we
can all compare "weapons" of choice?
Thanks Everybody...I hope this stirs the pot a little-bit
;0)
Brandon from Indiana
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