I decided to install a AFR gauge to see what the computer is doing. I assume that it should read slightly leaner than normal due to the groove even if the computer doesn’t adjust the mixture? So when I first ran it, it was showing around 15.2 and occasionally would go close to 16 at warm idle. Ran it a bit hard on my way home, then it stayed at about 14.5-15. On a flat road, when I let off the throttle, it would richen to about 13 briefly before it would lean out. Same at any RPM. Also it would be slightly richer when just barely on the gas then at normal cruising throttle position. Cruising flat it’ll stay around 15. I want to see how the computer reacts to EFIE. I saw a video of a guy who had this AFR gauge on some GM truck that had either a MAP or MAF enhancer. Every time he adjusted it, the computer would revert back to its normal fuel mixture within a couple of seconds.
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Vernon - you know what these meters actually tell you? how close to the scientifically optimum ratio of oxygen to "fuel" the engine is running at; if the computer is doing what it's supposed to be doing...at that given moment in time. it's an instantaneous readout. The ONLY gauge or meter that will tell you if you've made an improvement in efficiency is a calculator: divide the tripmeter distance since last fill by the number of gallons, an average over time. I wonder what it would've told you at the first start after putting the groove on?
I'd bet it would've been somewhere in the range of between 8 and 12:1, but the computer then leaned it back to 14.7ish:1, the scientifically determined perfect ratio for one mass of fuel to oxidize completely - it takes 14.7 masses of oxygen. 14.7 grams of oxygen to one gram of fuel...at standard temperature and pressure at sea level. since our atmosphere is roughly 78% Nitrogen and 21% oxygen, an engine has to suck in a LOT of "air" to burn the fuel it needs to run
14.7:1 is the bull's eye, but bulls have legs that move them, and they have eyelids that blink, and heads that turn and bob and twist. Like a bull rider at the rodeo, strap in and hold on as best you can!
remember - the computer continually adjusts based on sensor inputs, because engines do not run in a bubble. the atmosphere is in continual flux - temperature, pressure....and that ideal 14.7:1 ratio is for air at standard temperature (16 degrees centigrade or 61 F) at standard pressure (102.1 kPa IIRC or 29.92 inHg) at sea level. The specification doesn't include any accounting for humidity to the best of my knowledge...but it should.
Anyway, if the air temp rises, the air gets less dense, meaning there is less oxygen per unit (Mass air flow meters "weigh" the intake air - they read in grams per second. I'd love to know if that's total air or just the oxygen) and the computer interprets that as "I need to pulse the injectors for x seconds so that i deliver y milligrams of fuel". the engine scrunches the air-fuel charge, the spark plug lights it off, byproduct of combustion gets exhausted past the upstream o2 sensor which says back to the computer "too much", "not enough" or "just right" (which is why fuel trims should be zeros) and the cycle repeats. At the same time, pressure changes too - the MAP sensor tells the computer if the weight of the "air" the MAF sensor told it is correct, and if (and how) it needs to correct that last fuel delivery calculation, and again, it's verified by the o2 sensor.
Ok, long overdue update. I recently bought another frontier. It is a 2011 Pro4x. Same engine, so the throttle body will fit over which I already did. Its a wrecked salvage title and the repairs are done but still waiting on the paperwork so while I can’t drive it yet, the exhaust does smell clean!
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