Misfire cylinder #4
Verified cylinder #4 (and only #4) is misfiring via "which cylinder is misfiring" PID. More of a fishbite type at idle and will have more counts if you power brake it. First I started with a relative compression test. Sync is on #4 - blue trace at the pcm connector (access is terrible on this thing) Pulse sensor is the red trace. First thing I see is inconsistent firing voltage. Is this something to be concerned about?
I think you have a tiny hole in a spark plug boot. I'm not good on scope, but I have a lot of experience with 3.6 in Dodge Grand Caravans.
The only thing I see with your ignition is you have the sample rate too slow to properly capture the event. I also see one cylinder low on compression too.
I am not able to understand enough of your traces but I would move #4 coil with another to see if the trouble followed the coil. Maybe take a look at the plug too? It would have been nice to see some secondary ignition waveforms for me. What I do seem to see is inconsistency on #4 primary voltage making me think the firing is inconsistent.
Problems with cam and lifter wear on these. What is the mileage? I had both replaced on my personal 2016 with under 50K on it. It started to tick. No misfires yet. Is this one loud?
How many miles on this ???
Are the plugs original
Yes, factory champions.
I had same thing on same van and it ended out being a burn hole in the spark plug boot. Was obvious once I pulled intake plenum and coil. You are right real bear to properly test. The one I did got a set of boots and spark plugs because of mileage and has been fine since.
The inconsistent firing voltage is caused by the low Sample rate, also difficult to look at the spark plug burn times for misfires because of the low Sample rate. The transducer in CH B shows the repeating low pulse in cyl 4 caused by a worn cam lobe/lifter issue.
WE had one that the valve seat dropped- fortunately it was under factory warranty - Paul
hay paul How are you doing ??? this is randy from ASC . ran into your guys at the autologic scope class last month. send me a email would love to here from you . …
Pinhole in the plug boot. How did I come to this? I'll be honest that I'm not good at analyzing these waveforms to say theres an issue in the secondary without doing a visual inspectio on the coil and plug on #4 but based on what I'm seeing in my snap throttle test the burn line had a ton of oscillations. A secondary ignition problem, no?
Ha, looks exactly like the one I had. Start of a pattern on these. LOL. Same cylinder even.
In the first capture, the first ignition firing event has no spark time, so the spark is arcing thru the plug boot. In the other firing events, the spark is arcing across the spark plug air gaps to the plug's ground terminals.
Thanks Ray. How many captures do you typically get when analyzing misfires? Idle? Snap throttle? 3,000 rpm? Power brake?
For ignition misfires, take the captures at the rpm when the engine is misfiring. I prefer the brake torque because the compression rises, which can force the secondary spark to find an easier path to ground.
Hi Ray, I like the brake torque method also, I usually power brake at … rpm. It makes it easier to see if the fuel is running out causing the miss. I also found hard power brakes make it looks like everything is misfiring. Have you found the same?
Secondary can look confusing during the brake torque, on some makes. Try to capture the coil primary voltages, the coil primary voltages can look easier to diagnose. The first capture is an 07 F-150 5.4 at idle, with no misfires. The scope is on all 4 COPs on the left bank and you can save time by scoping 4 COPs at one time. The second capture is the same vehicle and I am doing a brake torque…