XPost: alt.home.repair, ca.driving   
   From: arlen_holder@newmachines.com   
      
   On 18 Nov 2020 13:17:51 -0000, Scott Dorsey wrote:   
      
   > What you want to know is in the graphs for the   
   > two O2 sensors and how they track.   
      
   Hi Scott,   
      
   Thanks for that gentle reminder, as I will borrow the vehicle today, but I   
   have to check it in their garage, as I only get one chance a day to test   
   warmup conditions (I think, at least, at Silicon Valley temperatures).   
      
   > But you will not figure the problem out just by looking at the plots, you   
   will   
   > figure the problem out by thinking about how the emission control system   
   works.   
      
   Well, to tell it to you bluntly, I'm not omnipotent.   
   o I didn't know anything when I first posted this thread   
      
   I didn't even know the _range_, which I've since learned is basically about   
   ~100 mV for lean conditions, to about ~900mv for rich conditions.   
      
   Nor did I know when I opened this thread, what the expected differences   
   were for the upstream versus downstream lambda sensors, where the front   
   should be changing far more frequently than the rear (which should read, as   
   much as possible, a stoichiometric ~450mv under steady warmed load).   
      
   What I didn't know at first was why voltages bounced all over the place.   
      
   But now I've boned up, a tiny bit, on the fact that the bouncing around of   
   the voltages is "normal", at least for the upstream side, since the engine   
   computer is constantly adjusting the ratio (within seconds) depending on a   
   whole bunch of factors, not the least of which is engine loading.   
      
   Further honing what I didn't realize at first is that there are two states:   
   1. Steady state (which is where most of my prior measurements lay), &   
   2. Warmup state (which is where I need to focus, as you had advised me).   
      
   What I need is what most sites don't provide, which is I need to learn more   
   about this warmup process of the cat, since it's a 'warmup efficiency' DTC.   
      
   I only get about a minute (or two at most), right?   
      
   >>When do I take the readings once the engine is warmed up?   
   >   
   > All the time.  You take them before it warms up, you take them after it warms   
   > up, you take them over the course of driving around.  What you are looking   
   for   
   > is trends and correlation more than specific values.   
      
   Yes. But.   
      
   I belatedly realized I need to focus specifically on 'warmup efficiency'.   
   o My main focus now revolves around how to diagnose 'warmup efficiency'.   
      
   Obviously I need to figure out what 'warmup' even means, which I need to do   
   as my homework, since I'm not even sure how long warmup of the cat lasts   
   (the sensors only take ~20 seconds to warm up, but I'm not sure how long it   
   takes the cat to warm up, nor, if a cat can even warm up twice in the same   
   day given Silicon Valley typical warm nightly & daily temperature ranges).   
      
   I'm gonna borrow the vehicle today but it's wet outside so I'm not sure if   
   I'm gonna crawl underneath to check the rear lambda sensor; but I will at   
   least check the live OBD data during the first 20 seconds of the lambda   
   sensor warmup and then the first few minutes, where I'm guessing a cat   
   warms up in, oh, I don't know, within the first five minutes perhaps?   
   o I'll look at an engine temperature reading (coolant perhaps?)   
   o Then I'll look at the front & rear sensors (and what they do over time)   
      
   I may need to buy an infrared thermometer to check how the cat warms up in   
   the first five minutes with the vehicle on jack stands; but no sense in   
   doing that until I learn more about how the cat _should_ warm up, as the   
   numbers won't mean anything if they're measured under the wrong sequence.   
      
   >>I don't have the necessary equipment to save or see graphs.   
   >>o I can only see the live data as it happens.   
   >   
   > Well, that's useless.  So you're going to have to plot it on semilog paper   
   > by hand.  Your scanner does not provide ANY plotting functions?   
      
   My OBD scanner _does_ provide plotting functions; but it's second hand (I   
   picked it up at a garage sale for a few bucks). It works fine for live   
   data, but I don't have the cabling or software to view the graphs.   
   o Harbor Freight item #60693 Cen-Tech OBDII/EOBD Deluxe Scanner   
      
   It also does 'freeze frame' but I haven't even started to look at what that   
   means to me, in terms of how I can use that to diagnose warmup efficiency.   
      
   In summary, I started out with the wrong assumptions, and I ran the wrong   
   tests, and I didn't know how the system worked... but I'm reducing my   
   ignorance by reading up on how the system works, and I'm gonna focus on the   
   all-important warmup process, where I think I only get one chance a day.   
   --   
   Experience is knowing which measurements to take, when, where, & why.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)