Updated fueling info . . . and undetermined causes.

[boostjunkie]

Okay, well I wired in the S-AFC the other weekend (unfortunately, the wiring diagram I was looking at was completely WRONG!! ARRRGGHH!!). In the process I found out that the wire I was tapping into for the injector duty monitor was injector #1. I figured it'd be better to tap off of injector #3 since that cylinder tends to run the leanest. So . . . two things:

1. Whereas injector #1 was running 100% duty cycle at 1bar, injector #3 is running 80% duty cycle at 1.1bar(!!). No changes were made to the car besides switching the injector tapped into.

2. This weekend, while tweaking the boostcontroller, I upped the boost just a little. Hehe, boost peaks now at 1.1BAR/16.2psi and guess what? A/F ratios remain just on the rich side of things.

Um, I'm totally confused here since three weeks ago my A/F was reading stoich at 1.03 bar . . . now, all of a sudden I can run 1.10bar?!?!?! I'm thinking maybe the gas I'm getting is not the winterized gas? Maybe the change in weather (it wasn't 0 degrees out, more like 40's)?

Any ideas what could change this sudden boost in performance? I'm completely stumped!! Please discuss . . .

[Aaron's ej22t]

i am not exactly sure on this, but i heard that some a/f gauges are not totally accurate. i have a autometer a/f, and i am thinking about selling it. i never installed it.

[morgie]

in fact, it's not the gauge that isn't accurage, but the sensor itself !

here is a doc. on how a o2 sensor works, pretty interesting :
http://www.autospeed.com/A_0618/page1.html

[boostjunkie]

I actually already knew this, however, here is why I still am using the devise (other than not having enough money for an EGT right now:D). Taken from your literature:

"This diagram (Ford) shows the typical output characteristic of a zirconia oxygen sensor. As can be seen, the output voltage exhibits a rapid switch around air/fuel ratios of 14.7:1. This is the characteristic curve output of a Narrow Band oxygen sensor, as used in most cars."

Okay, so we know that there is a drastic change in voltage between the ranges of stoichiometric A/F ratios. However, we also know that at rich A/F ratios the voltages level out, and the o2 sensor is outputting more accurately (at least more accurately than when in the stoich area). Tuners tend to run their A/F ratios on the rich side of the stoich spectrum - the rich side (but not overly rich). Reason being that under normal conditions, proper combustion of most of the gas mixture is obtained in this set of ratios (without raising EGTs to the point of failure). There is no real problems with running more rich than that (which is what I seem to be doing, but I still could be wrong, I know), other than possibly bogging the engine or mucking up the cat/o2 sensor faster. A/F are definitely in the rich side, there's no mistaking that. All the way over on the gauge. Not in the stoich at all. No, it's not optimal, but it is safe.

"In addition to the air/fuel ratio, the output voltage of the sensor is heavily dependent on its temperature. As indicated earlier, at very low temperatures - below about 350 degrees C - the ceramic material is insufficiently conductive to allow the sensor to function correctly."

Since the sensor's insufficiently conductive at lower temps, I should start to see a change in the sensor readings as: 1, the engine temp increases,
2, cylinder/EG temps rise causing a resultant exhaust temperature increase, or 3, change in ambient air temps (did I mention that for the first time in about 2 months the temps around here were significantly higher than 10 degrees?). However, the change in o2 sensor readings would lean towards the lean side of the spectrum with temperature increases to the o2 sensor, not towards the rich side. Case in point:

"This means that, at high temperatures, oxygen sensors typical read leaner than the actual air/fuel ratio."
I'm still in the rich (read: safe) area of the A/F spectrum. Again, not optimal . . . but definitely safe.

Thanks for the link, though. I didn't know that temperature affected the sensor voltage that much!!

[Aaron's ej22t]

you're right morgie! i forgot that you need a wideband 02 sensor to get accurate readings.