Stock AFR questions
08-08-2016, 11:00 PM
#1
Three Wheelin'
Thread Starter
Stock AFR questions
I just installed an AEM widedband O2 sensor in the hope it would help me to track down some intermittent issues I'm having. For the most part it looks like my AFR is fine now but I have a few questions for anyone who knows...
* What AFR should I see when accelerating at part throttle, with boost? What I'm seeing is that it drops from mid/high 14s (idle/light throttle) down to low/mid 14s. I never really see it dip below 14.2 - even on boost - unless I go to WOT (which gets me instantly down to high 11s). Is that normal? It's hard to find clear info on what it should be.
* idle AFR is pretty stable around 14.6 or 14.7, except for one condition, which seems to be pretty consistent: if I stop the engine while warm and let it sit for around 15-20 minutes, then when I start it again it idles very lean - high 15s to high 16s. It seems to do this as long as I sit there, but if I move, even a hundred feet, then check it again, idle AFR is back to normal. I thought this might be caused by the water temp going up when the engine sits, which is detected by the DME temp sensor and that makes it go leaner, but once the water starts pumping again it cools down a little and goes back to normal?
Maybe these things are perfectly normal - they don't seem to be causing any problems I can see anyway, I'm just curious because I've never had an AFR gauge before. Thanks!
* What AFR should I see when accelerating at part throttle, with boost? What I'm seeing is that it drops from mid/high 14s (idle/light throttle) down to low/mid 14s. I never really see it dip below 14.2 - even on boost - unless I go to WOT (which gets me instantly down to high 11s). Is that normal? It's hard to find clear info on what it should be.
* idle AFR is pretty stable around 14.6 or 14.7, except for one condition, which seems to be pretty consistent: if I stop the engine while warm and let it sit for around 15-20 minutes, then when I start it again it idles very lean - high 15s to high 16s. It seems to do this as long as I sit there, but if I move, even a hundred feet, then check it again, idle AFR is back to normal. I thought this might be caused by the water temp going up when the engine sits, which is detected by the DME temp sensor and that makes it go leaner, but once the water starts pumping again it cools down a little and goes back to normal?
Maybe these things are perfectly normal - they don't seem to be causing any problems I can see anyway, I'm just curious because I've never had an AFR gauge before. Thanks!
08-08-2016, 11:17 PM
#2
Those ranges are pretty good, I use AEM a/f kit as well. At idle my 86 is 14-15.2 or so which is consistent. Wot is usually buried at 10.5 in summer which is relatively rich right now but my goal would be 11.5 - 12 or so if it was colder out at Wot.