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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

Files Referenced:

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car Vehicle Data

2005 Honda Pilot EX 3.5L

Engine3.5 L
Trans5-speed Automatic (Electronic)