Idle afr question.
Jan 9, 2014, 07:45 PM
#1
Idle afr question.
Ok before people jump and say "search" let me explain. My question is what is a normal afr at idle? I always hear its 14.7 but every time I see a video of a built evo the afr's are always all over the place during idle(complete stop). My car does the same. Matter of fact I've never seen a steady afr from idle on a car, is this normal? Is the 14.7 just for cruising? Thanks
Jan 9, 2014, 07:49 PM
#2
There are alot of factors that go into what idle should be. You will most likely never see a steady number at idle, especially once mods come into the picture. I have 2150cc injectors powered by a hard wired 450 lph fuel pump on stock fpr. I also have gsc s2 cams and my idle is in between 14.6 and 15.3.
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Jan 9, 2014, 11:17 PM
#11
EvoM Community Team Leader
with really aggressive cams some tuners will richen up the idle to help stabilize it. I dont know if this is common on evos or not though. This is done either by narrow band simulation via a wideband or by preventing closed loop and just tuning the fuel maps.
If you look at your fuel trims (LTFT Low + STFT) and they arent +/- 5% or so then you are perfectly normal. I think anything above 12-15% will throw a CEL. The reason you see it bouncing around is because the engine is running in closed loop and is hunting for that perfect 14.7 AFR for emissions reasons. The engine doesn't need to be at 14.7afr it can idle much leaner/richer just fine. The reason for it is purely to produce the lowest possible emissions.
If you look at your fuel trims (LTFT Low + STFT) and they arent +/- 5% or so then you are perfectly normal. I think anything above 12-15% will throw a CEL. The reason you see it bouncing around is because the engine is running in closed loop and is hunting for that perfect 14.7 AFR for emissions reasons. The engine doesn't need to be at 14.7afr it can idle much leaner/richer just fine. The reason for it is purely to produce the lowest possible emissions.
Jan 9, 2014, 11:46 PM
#12
with really aggressive cams some tuners will richen up the idle to help stabilize it. I dont know if this is common on evos or not though. This is done either by narrow band simulation via a wideband or by preventing closed loop and just tuning the fuel maps.
If you look at your fuel trims (LTFT Low + STFT) and they arent +/- 5% or so then you are perfectly normal. I think anything above 12-15% will throw a CEL. The reason you see it bouncing around is because the engine is running in closed loop and is hunting for that perfect 14.7 AFR for emissions reasons. The engine doesn't need to be at 14.7afr it can idle much leaner/richer just fine. The reason for it is purely to produce the lowest possible emissions.
If you look at your fuel trims (LTFT Low + STFT) and they arent +/- 5% or so then you are perfectly normal. I think anything above 12-15% will throw a CEL. The reason you see it bouncing around is because the engine is running in closed loop and is hunting for that perfect 14.7 AFR for emissions reasons. The engine doesn't need to be at 14.7afr it can idle much leaner/richer just fine. The reason for it is purely to produce the lowest possible emissions.
Jan 10, 2014, 05:15 AM
#13
If you look at your fuel trims (LTFT Low + STFT) and they arent +/- 5% or so then you are perfectly normal. I think anything above 12-15% will throw a CEL. The reason you see it bouncing around is because the engine is running in closed loop and is hunting for that perfect 14.7 AFR for emissions reasons. The engine doesn't need to be at 14.7afr it can idle much leaner/richer just fine. The reason for it is purely to produce the lowest possible emissions.
