V-Pro Simultaneous Waveforms

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  • Because
    Member
    • Jul 2010
    • 72

    V-Pro Simultaneous Waveforms

    I am relatively inexperienced when it comes to using a scope for diagnostics. I have owned a V-Pro for 5 years. I owned a Modis before that. I just don't use the scope that much. I think my reluctance to use it stems from the fact that it takes SOOOO long to get the correct setup, get the funky connections working, and finally getting useable screens that are trust worthy. I can diagnose most problems using scan data, DVOM, or physical inspection faster. MUCH faster. So that's been my way of doing things. I'm sure the V-Pro could actually make many jobs even faster, but it never seems to work that way for me. I end up screwing around with the V-Pro for a ridiculous amount of time then reverting to tried and true diagnostic processes that work for me.

    One of my biggest stumbling blocks is trying to compare two waveforms simultaneously. Here's a perfect example. I wanted to compare Crank Sensor (CKP) and one Cam Sensor (CMP) on a 2004 5.4l 3 valve Ford. I suspected jumped timing. I hooked up channel 1 to the yellow / black leads and backprobed the CKP + / - signals at the PCM. I hooked up channel 2 to the green / piggybacked black leads and backprobed the CKP signal wire at the CKP. After some fiddling with positioning and resolution, I got a good CKP waveform. I also got a CMP waveform, but it was a marriage of both the CKP and CMP signals. I could see the 'hits' of the CKP reluctor passing the sensor. But the CMP signal was riding on channel 2 as well as channel 1. It made the channel 2 waveform unreadable. I don't understand why this happens. What's worse is that I have performed this test successfully in the past on an identical engine. So I know it can be done. It is just frustrating that every time I go to use the V-Pro, I have to spend an hour or more trying to figure out how to make it do what I want.

    I ran into a similar problem a while back trying to watch front analog ABS wheel speed sensors on a 2004 Buick Rendezvous. It was seemingly impossible. The signals were blended together and both waveforms had simultaneous data even though they were from separate sensors.

    It is my inexperienced opinion that the common ground for the two channels is the source of my problem. How can it be possible to have two channels share a common ground point (or negative point)? can anybody offer advice on what I am doing wrong? I know practice makes perfect. I've tried really hard to get this and I'm not getting it. Any help would be greatly appreciated.
  • Witsend
    Banned
    • Nov 2012
    • 2942

    #2
    As long as where the grounding point for the scope is at is indeed clean and there is little or no voltage drop between it and the negative battery post, then the issue about the 2 channels sharing a common grounding point is a non issue. If you can somehow keep the sides of wires of the probes away from secondary ignition coils, alternator , and injectors that can generate interference.
    Hey, I thought one of the benefits of the Vantage Pro and up ,was they were supposed to be easier to use than a Counselor 2 or Pico, because they could automatically sense ,adjust the time and voltage range to see a useable trace or advise over range -need attenuator! and you could then tweak things from there with out having to be a mad scientist turning knobs and such, and screaming , "It's Alive!" when you finally see a good trace.LOL
    Last edited by Witsend; 06-21-2015, 08:22 AM.

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