SomeBuckaroo Posted February 6 Share Posted February 6 Moses, I finally got around to 'scoping up my TJ for further diagnosis. I've attached pictures of various traces. A few notes: CH1: Cyl 1 Spark Plug Wire (via capacitive probe) CH2: Spark Coil Wire (via capacitive probe) CH3: MAP Sensor Signal My capacitive probes are cheap and I think the probe on CH1 (Cyl 1 plug wire) may be degraded. It works well enough to trigger the 'scope, and the probe on CH2 seems to do a fine job picking up the coil spark train. OR: is this degradation actually evidence of an issue? I've replaced the cap & rotor several times with no change to my symptoms. I should have swapped the probes to see if the weak signal followed the probe. Also note the noise on CH3 (MAP sensor signal), seemingly uncorrelated with injectors or spark plug firing. Is that amount of noise normal? I wonder from where it's coming, how much is present on the other sensor lines, and what effect it has. I wish I had reference signal traces of a known-good 4.0L. Regardless, it does appear that the MAP sensor has sufficient bandwidth to capture manifold vacuum fluctuations within the firing order. Pretty cool! I've tried to choose filenames that describe the activity being shown. I'm happy to do additional rounds of scope work, adjust the time-base, delay the trigger to capture each cylinder individually, etc. I do know that features of spark waveforms can be used for troubleshooting, but I am not at all versed in that area. Let me know if any of this helps! Quote Link to comment Share on other sites More sharing options...
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