Analyzing Ignition Waveforms
My daughter drives a 2002 Xterra 3.3 that has had an intermittent misfire. I have never been able to experience this misfire, but it has set a P0304. Due to her description of the misfire, "It wiggles when you first start it, and the check engine light flashes. But stops wiggling after a few minutes or if you shut it off for a few minutes and then restart." When I ask her if it was a cold start or a hot restart, she said mostly a hot restart. I was thinking it had a leaking injector. So I moved the #4 injector to #3 and let her have it back and it set a P0303. So I replaced the suspect injector. I am confident I have repaired the misfire but I don't like the looks of the ignition waveform. The attached file is of the ignition system. Primary voltage at the distributor and secondary on Cylinder #1 plug wire. I am a little concerned about the nose at the end of the spark line. But hoping someone with more experience can help me to understand the capture. Idle fuel trims are B1 +4.6 and B2 -1.4
On another note when I tested the injectors with a current probe injectors 2-6 were all 1.05-1.1 A but injector #1 was right around 840 mA. My question on that is would that be enough to rightfully suggest that a customer replace that injector? As a preventative measure. I went ahead and replaced it on this one just because I was there and she spends most of her time 5 hours away at school.
It looks like your waveforms were taken at idle? Secondary ignition is active, therefore, you need to move the throttle a little to get your scope to snoop out problems. I grabbed a capture from your waveforms and put some notations on it. To be a little more accurate with your waveforms, can you get a parade of the secondary voltage? Primary voltage is OK, although, the secondary can be a
How many miles? Have you tried cleaning the other injectors? It isn't uncommon for these to clog up and cause issues, sometimes all cylinders clog fairly even. Try the ignition test again with a snap throttle, hopefully this video helps: youtu.be/68z3UZvg26Y
My question because I’m new to looking at secondary ignition relation to drivability issues is I see the sharper down slope of the burn line which I would think is resistance outside of the combustion chamber how do we know that this is a true lean cylinder?.
Tom, the shape of the waveform is caused by the energy stored in the ignition coil, the resistance in the secondary ignition and the resistance in the plug gap. The resistance in the secondary, in the case of this vehicle, is the spark plug wire and the spark plug, down to the spark plug gap. This resistance is fixed, as, it will not change with engine load. The resistance in the spark plug gap
That is why I do it with a snap throttle - injector flow pattern and volume will be more noticeable when there is supposed to be fuel enrichment.
I wasn't able to get any other waveforms before she had to leave for school. But to clarify, it runs well with no misfires. It was setting a P0304 very intermittently that I was never able to duplicate. Due to her description of the misfire I moved the #4 injector to #3 and later when it misfired for her it set a P0303. I replaced that injector and injector #1 due to increased resistance.