joshbuys Posted April 25, 2012 Share Posted April 25, 2012 Engine theory question one of our ASSET apprentices asked me, and I'm not certain how to answer? Does an engine run rich or lean during warmup? Running lean definately runs hotter, but too lean will get NOx emmisions. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted April 25, 2012 Share Posted April 25, 2012 The patent answer used to be rich - even with EFI, cold combustion chambers didn't light off real good. In carburetted engines, we would see either a choke plate restrict airflow above the venturis moving the vacuum signal further up into the carb - additionally, the throttle plates would be held further open uncovering the transfer slots (above the idle jets) resulting in more fuel entering the cylinders. Other carbs used a "tickler" or enrichener that would increase the area of the jet or add a second fuel jet to the circuit. EFI engines from the 80s would require several minutes of enriched running to get the O2 sensors up to temp as well as heat the catalysts enough to fire up. Modern engines have the O2s start generating useful signals after only a few seconds of running allowing the PCM to begin responding to O2 feedback. Secondary air injection to the cats brings them up to temp quicker, too. Used to be O2 sensors didn't have heaters and this affected their time to temp. Also, the newer UEGO sensors we see now respond differently allowing far more precise fuel control than we ever had previously. I am assuming that, because it is what it is, we still begin with a mixture richer than stoich but with the state of the art regarding fuel control allows leaning things down much quicker than we ever could before. Probably more than you asked for, but "richer" without part of a why or part of a how isn't much to go on. Quote Link to comment Share on other sites More sharing options...
joshbuys Posted April 25, 2012 Author Share Posted April 25, 2012 Probably more than you asked for, but "richer" without part of a why or part of a how isn't much to go on. Not at all!! For me to be able to explain why it's one way or the other, I need to have some understanding Quote Link to comment Share on other sites More sharing options...
wring09 Posted May 16, 2012 Share Posted May 16, 2012 Wouldn't have thought that question took much thought and im an asset apprentice also, what had you stumped? Quote Link to comment Share on other sites More sharing options...
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