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).

Well the reason I said what I said is because if you read this article:

https://asia.vtec.net/spfeature/vtecimpl/vtec1.html

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.

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 some good info to help identifying the pins.

https://technet.ff-squad.com/wiring.obd1.htm

That page is very helpful, thanks.

Here's a pic of the Econo Light that came on federal VX's. Mine is a 92 VX bought originally in Wisconsin.

https://suspendedhatch.thecarthing.co...cono_light.jpg

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.

Thanks for that clear and helpful explanation.

"They are two strategies working together."

That's what I thought.

"But there are even more things going on here."

You provided a good list. Also worth mentioning: wheels and tires that are low weight and LRR (playing a role in reducing engine load).

"they'll idle lower due to less valve train friction"

I think on the VX a lower idle was a deliberate design decision (rather than a consequence of less valve-train friction).

A really good technical listing of all the VX FE ingredients is in this pdf. (I imagine you've seen that paper, but maybe others haven't.)

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)

https://asia.vtec.net/spfeature/vtecimpl/vtec1.html

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.

TomO are you making this top secret device? If so, how about some more info?

Nope, I'm not the creator of this device, and actually, it's no secret. It's being discussed openly at one of the other FE forums.

This is the only forum I visit, so if anyone knows what forum has this info, please post.

My guess is that maybe he's talking about this:

https://forum.ecomodder.com/forumdisp...mputer-26.html

That would be the one ;)

Very interesting but quite complicated for an electrical novice like myself.

Good luck on working through the bugs on that awesome device. :thumbup:

"but quite complicated for an electrical novice like myself"

I'm getting helpful info from a simple DMM. At Harbor Freight they start at $4. That would be enough to monitor mixture (lean burn). I paid more ($33) for a meter with a dwell-angle feature. That lets me monitor how long my injectors are open, which is a direct measure of true, instantaneous fuel consumption.

It's not hard to do. I'd be glad to explain how to do it.

I just looked at the 96 - 98 Civic Helm shop manual. It seems that instead of a test harness to connect to the ECU, back probe pin adapters are used on a standard DMM to connect to the pin outs on the ECU.

Has anyone tried this? It looks like it would work to access D14 and D16.

"Has anyone tried this?"

I think some kind of back probe would work fine. Like this:

https://www.backprobe.com/
https://www.smartchargers.com/products/22

Or this:

https://www.amazon.com/Automotive-Bac.../dp/B000I16DKM

But I wanted something cheaper, that I could find locally. Radio Shack had the perfect thing:

https://www.radioshack.com/sm-quick-s...i-2998435.html

Too bad there's no picture. These are called Quick Splice Connectors or T-Tap Connectors. Some more:

https://www.mouser.com/search/Product...538-19216-0018

https://www.vanco-online.com/index.ph...ucts_id=101458

https://www.magnadyne.com/index.cfm?M...&Web_CatID=193

Each approach has its own advantages. The RS product worked great for me, for this exact purpose (tapping wires near the ECU).

I tapped D14 and D16, to monitor AFR. I also tapped A1, to monitor the injectors (this requires a DMM with dwell, but I found one for only $33). This is very helpful, because it gives me a precise indication of instantaneous fuel use.

I also tapped D18, because my car has no SIL (shift indicator light), and I was curious what it would be like to have one.

There are some other interesting things to tap, but so far I haven't bothered.

I've also become very interested in the possibility of using a cheap ($25-50) data-acquisition interface to display/capture all this data on a laptop, instead of a DMM. I think that creates all sorts of interesting possibilities, greatly exceeding what a Scangauge can do. I wonder if anyone here has any thoughts about this idea.