I've always thought that lean burn was a result of the vtec-e mechanism. Here's a piece from wiki: SOHC VTEC-E
Honda's next version of VTEC, VTEC-E, was used in a slightly different way; instead of optimising performance at high RPM, it was used to increase efficiency at low RPM. At low RPM, one of the two intake valves is only allowed to open a very small amount, increasing the fuel/air atomization in the cylinder and thus allowing a leaner mixture to be used. As the engine's speed increases, both valves are needed to supply sufficient mixture. A sliding pin, which is pressured by oil, as in the regular VTEC, is used to connect both valves together and allows the full opening of the second valve.
So this should mean that if the vtec mechanism in a vtec-e engine were disabled, then it'd always be in lean burn? Correct me if I'm wrong, but if this were the case, wouldn't lean burn monitoring just be as simple as finding out whether or not vtec has engaged?
"I've always thought that lean burn was a result of the vtec-e mechanism"
I think the two things are related, but I'm not sure they're exactly simultaneous in the way you described. Anyway, there's a somewhat more complete explanation in this pdf. See Appendix A (printed page #19, pdf page #22).
The author will talk about the 3 stage vtec mechanism and says stage 1 is "Below 2500rpm and with gentle accelerator pressure, neither pin gets actuated. The engine operates in 12V mode with very good fuel combustion efficiency" (which is basically vtec-e with no actuation of vtec).
Then he goes on to say "Stage-1 12V or "lean-burn" operation mode is indicated to the driver by an LED on the dashboard. The 2500rpm cutover from lean-burn to normal 16V operation in fact varies according to load and driver requirements. With gentle driving, lean-burn can operate up to 3000rpm or higher"
I'm not sure if this technology was applied to the earlier 92-95 civics but it seems like lean burn mode on those engines was simply an indicator of whether it was in the first "vtec" stage or not.
"I'm not sure if this technology was applied to the earlier 92-95 civics"
Maybe you already realize this, but the passage you cited is discussing an engine that didn't exist back then. Other passages in the article discuss the earlier engine, but it's important to be clear about which engine is which.
"it seems like lean burn mode on those engines was simply an indicator of whether it was in the first 'vtec' stage or not."
Both techniques are happening, and they're happening at roughly the same time, but they're still two different techniques. And I don't think it's safe to assume that the VTEC transition is simultaneous with the lean-burn transition.
I would like to have light that tell me when the Lean Burn is on. I'm wondering why Honda didn't put one from the factory, still its a 1992 model...
Actually they did. My 1992 VX was originally purchased in Wisconsin. On the instrument cluster to the right of the trunk-open indicator, there is a white outline surrounding an arrow pointing up. It lights up green when you exceed 2500 RPM below 5th gear. According to the owners manual it is telling you to upshift. The VX was designed with a lightweight flywheel and with engine breathing characteristics in order for it to cruise at just under 1000 RPM. Without this shift indicator light, most owners would never cruise that low.
UNFORTUNATLEY FOR ME, the gas gauge went bad and always indicated full, so I had to replace that portion of the cluster with one from an Si. I kept the cluster face though. I can take a picture and post it up if you would like.
If you want to tap into some O2 sensor wires without cutting and splicing, you can use a technique that I came up with for a similar purpose. It will not be so easy to find the parts due to the rarity of the VX however, but what you would do is get a dead O2 sensor, cut off the plug, then find a junkyard VX, cut off the ECU side of the plug. Now wire together all the wires you don't need to tap into and bypass the two wires you need to go to your circuit then back again. Then you simply plug this homemade adapter inline with your O2 sensor.
"It will not be so easy to find the parts due to the rarity of the VX"
The method you're suggesting can be implemented without finding a VX to cannibalize.
The VX LAF (wideband O2 sensor) uses an 8-pin connector (even though it has only 5 visible wires). That same connector is used in various places on other EG Hondas (and maybe non-EG Hondas also).
See page 23-16 of the Helms manual. C125 and C107 are used on every '92-'95 Civic, and they are the same connector as what's used on the VX O2 sensor. The next page of the manual illustrates where these connectors can be found under the hood. And I think the same connector might be found elsewhere in the car.
But I think it would probably be easier to just use a 3M tap connector, as suggested earlier in this thread by darkelf, here. Then the wire could be tapped near the ECU. This means no need to run a new wire through the firewall. Also seems like a lot less effort with regard to cutting/soldering/taping.
Here's a pic of the Econo Light that came on federal VX's. Mine is a 92 VX bought originally in Wisconsin.
To the discussion that was going on earlier, VTEC-E makes lean burn possible because it creates a swirl in the combustion chamber, but they are not the same thing. They are two strategies working together. The other big part of the equation is the wideband O2. But there are even more things going on here. There's the EGR, the light-weight flywheel, the light-weight crank pulley (no harmonic damping), the lack of power steering, the front air dam, and the rear diffuser. All these work together to minimize load on the engine to allow it to run low RPM and not require as much power. More load on the engine requires more fuel and less ignition timing advance, and the converse is true of less load.
The CA VX's have VTEC-E but not the wideband O2. They run somewhat lean but not as lean as the federal VX's. The federal VX's had VTEC-E AND a wideband O2.
W/out VTEC-E, if you try to run as lean as 17:1 or higher, you'll misfire. You can't run that lean on any other Honda motors even though they are very similar. And you can't run a VX motor on 16 valves and run that lean. The fuel molecules are spread too far apart to get a good burn.
Close one intake valve and the air enters from one "corner" of the combustion chamber, swirling around the edge to the closed intake valve. This disperses the fuel evenly allowing you to run leaner yet get an even charge for an even burn with no lean misfire.
And yes, VTEC-E is VTEC-E, whether is a D15Z1, D15Z7, D16Y5, or the Civic VP engine (D16B5 I believe). The 96+ heads (OBD2) had larger valves, larger intake runners, and more quench area, so the tuning calibration will look very different. Only the Z1 and Y5 had roller rockers, so they'll idle lower due to less valve train friction. But the entire principle is the same.