Not trying to start a ruckus or anything, but the 3 stage VTEC D15B also has VTEC-E but only uses a 1 wire O2 sensor (if I'm not mistaken) while enabling lean burn to be possible (?).
The reason I've been wondering and researching this is because I am trying to figure out how the ECONO light in the cluster of those cars are turned on. I reached the conclusion that it would simply be a matter of it being in VTEC-E mode that turned it on, but maybe there are other factors that switch that light on.
Hah ha. That's not exactly controversial or anything. You certainly wouldn't be hurting my feelings by speaking the truth. Mine only came with a one wire O2 to my surprise. It's not actually a big deal and it certainly doesn't mean that the ECU doesn't run lean.
One wire O2 lacks a heater. The heater is used simply to get the sensor up to operating temperature sooner. And of course it's not a wideband but neither is the CA VX.
The CA VX lacks a wideband yet it runs lean. It's simply a matter of carefully tuned fuel maps and open loop. The wideband is only accurate to 18:1 mixtures, yet people have claimed that the ECU runs as lean as 25:1. If this is true then it proves that the ECU is running open loop at cruising loads and is probably only using O2 feedback for partial throttle acceleration.
O2 feedback isn't necessary but it's quite helpful to maintain optimal mixtures and correct for different conditions including worn out sensors and lack of engine maintenance.
As for the upshift light, it's pinned directly to the ECU. I'm sure the ECU does a simple compare and outputs power at the appropriate times. To know when you're in fifth gear it just needs to know vehicle speed and RPM. There's no reason for it to monitor the O2. It can just make a simple assumption based on load and RPM.
I was referring to the 96+ EK3 vti and similar vehicles with the D15B motors that had an ECONO light on their dash instead of an upshift light in the VXs. It's supposedly a "lean burn monitor" according to this article (in the part where it talks about the 3 stage vtec)
But since you mentioned it, I wonder if it'd be possible to make a DIY upshift light since the VX supposedly already has the outputs for the indicator light.
Apologies to the original poster for all the off topic discussions.
"I reached the conclusion that it would simply be a matter of it being in VTEC-E mode that turned it on"
I know you're talking about a different motor, but here are some thoughts about the VX.
According to the Helms manual (page 5-7), VTEC on the D15Z1 engages at 2500 rpm (assuming certain other conditions of temperature, vehicle speed and load). Is that when the SIL (shift indicator light) comes on? I thought I saw someone mention it comes on about 1600 rpm. Anyway, 2500 seems too high for the SIL.
My VX still has the CA instrument pod, with no SIL, although I've given it the federal O2 sensor and ECU.
I know there's a pin on the ECU that drives that light (as suspended mentioned), and another pin that drives the VTEC solenoid. And of course pins that indicate what the O2 sensor is doing. Someday when I have some time I'd like to use a DMM to look into what's happening on those pins, while I'm driving.
It would be nice if the original Honda engineers stopped by and explained all the secrets they packed inside the ECU. Although I'm grateful that there are people here who know so much more than I do.
"I wonder if it'd be possible to make a DIY upshift light since the VX supposedly already has the outputs for the indicator light."
I suppose you must be talking about a CA VX. Because the federal VX already has the SIL.
.................The other issue that I have with my project though is the fact that there is a display device that is currently being constructed that will give you about as much information as a SuperMID does, but only cost around $70 total investment....
TomO are you making this top secret device? If so, how about some more info?