Fooling the ECU to burn lean...

[wagonman76]

I built an O2 modifier circuit from a document floating around called D17.pdf. I tried it in both cars (the Celeb and an 89 6000 with 2.8) and no matter what I did, mileage went down a little when leaning a little, and went down a lot when leaning a lot. Perhaps it would be better suited for applications when part of the gas is being replaced with something else. It also seems that the inline battery method might be a better idea.

[gteclass]

I wouldnt go changing the o2 voltage by force. Narrow band stock o2s are only accurate at .5 volts(some sources say .45) and that is because they act like on off switches. Higher than .5 means rich, lower means lean. When you change the voltage from .5 to .6 it just switches at .6 causing the car to constantly think it is running rich and constantly build negative fuel trims.

O2 sensors are used in a closed loop feedback system to generate these fuel trims. Most cars have short term trims which run directly off the sensor reading in real time, and long term trims which are based on historical data that your ecu stores and are pretty much an average of your short term trims. You can log these fuel trims using any obd2 logger and you will always get the best economy/performance/drivability when they all average out to zero for every load/rpm. This can only be achieved with some piggyback tuning as there are variances manufactured into the car.

The only way I would suggest altering your cars idea of Stoich or the target closed loop afr is to get an Innovate LC1 wideband controller which has 2 programmable analog outputs. You can set one to read .1 volt for anything leaner than say 15.5 and .9 volts for anything richer than say 14.9 this way your computer will see a switching voltage of .5 and you can accurately tune what the appropriate switching afr is. Also, you can mount a cheap 25$ afr guage and program the LC1s secondary output to be say 1 volt at 12:1 and 0 volts at say 16:1 and get an idea of where your car really runs and also monitor your open loop operation to make sure it doesnt go too lean.

Your ecu bases its open loop operation on the closed loop developed fuel trims. It is basically guessing what ammount of fuel will be necessary to achieve a safe afr under heavy loads. If you are at wide open throttle(WOT at 2000 rpm is like open 30% before someone says you will never save fuel at WOT, you also would never make it up the hill at 2000rpm without going to WOT) going up a steep hill your engine wont last very long running a 15:1 afr. Be careful how lean you run in closed loop because it will have and effect on your open loop operation.

BTW... Lean burn engines tend to have staggered intake cam profiles within the cylinder so if you have 4 valves per cylinder you might be able to get custom ground lean burn cams. Wiki search the MVV ( Mitsubishi Verticle Vortex ) engine for more info. BTW most cars do have a slightly staggered intake cam profile anyway so we still might get to burn leaner efficiently without a set of cams.

[metromizer]

Holy cow! The wealth of information here <on this forum> is nothing short of incredible! Thanks to those who have welcomed me, and a huge thanks to everyone who spent the time putting together very informative and understandable replies.

As I said, I don't know much about EFI systems (I appreciate your patience), all of my past tuning has been with carburators and mechanical fuel injection (MFI) systems, but those were WOT drag race applications, that have little in common with with what I'm doing.

let me see if I have this right; Narrow band O2 sensors used in OEM's help the computer learn what fuel map to employ the 'next time', but that could vary from ECU brand to ECU. I fully understand that pulling fuel away and burning a little lean isn't going to change the basic design (limitions) of my 3 cylinder Suzuki, but employing a few complimenatry changes might get me to my goal 50mpg at 65mph.

I have a head and cam change in the works, used stuff I will have reconditioned (taken off a Metro XFi) I'm contracting out for a little port match, bowl, and valve work by a proffesional head porter I know, I might bump the compression ratio up a little and file in some Singh grooves while I'm at it, for those who fiddle with Suzuki's.

From my race tuning I know that typically most race cars are running way too rich, safe, but rich and lower on power than they otherwise could be. I am wondering if my little Metro isn't also running a little on the rich (safe) side by design, to accomodate poor/uneducated driving technique, hot weather and marginal fuel, as to keep warrenty repairs at a minimum. I wonder if I could manually trim back the amount of fuel the engine gets under ceratin conditions, which BTW is where this commuter spends most of it's operating time, 65mph for about 1 hour per day. If I could reduce fuel consumption by 10% by trimming fuel, the excersize would be a success.

Catalitic converted overheat? noted... those things aren't cheap to replace.

Carlos: Was your O2 circuit 'voltage adder' ever successful on your car?

[cfg83]

metromizer -

Originally Posted by metromizer

Holy cow! The wealth of information here <on this forum> is nothing short of incredible! Thanks to those who have welcomed me, and a huge thanks to everyone who spent the time putting together very informative and understandable replies.

...

Carlos: Was your O2 circuit 'voltage adder' ever successful on your car?

I think it is because I can *see* the A/F ratio creep up when I drive, but you need to read my whacky explanation in my thread. It doesn't settle at a new A/F ratio. It climbs up above 14.7, and then jumps back. I think this is because the lean signal from the second 02 sensor triggers logic in the ECU/PCM to keep the cat healthy (that's a good thing).

Maybe I will make a new YouTube demonstrating the behavior I am describing.

CarloSW2

[ZachUA]

I have a 98 civic ex. Does anyone know if it's possible to convert it to a vx without swapping the whole motor? I'm wondering if it's possible to simply replace some of the current motors components and then reprogram the computer so that it has lean burn?

[Streak]

Originally Posted by cfg83

metromizer -

Welcome to EM! Here's mine (I flip a switch just like you said) :

My Eagle Research EFIE
http://ecomodder.com/forum/showthrea...efie-1308.html

I don't use it much except for testing. I don't want to make it part of my overall system until I can verify emissions compliance.

CarloSW2

Bingo. Unless you guys are concerned only with your wallet, these lean burn systems aren't good in a holistic sense. (As explained in the post below this one)

Originally Posted by MechEngVT

You also don't want to run lean-burn for too long because you may cause damage to your catalytic converter. The cats require the switching between lean/rich to properly function as both an oxidation and reduction catalyst. The cat needs a lean mixture to oxidize HC and CO, but then needs a rich mixture to reduce NOx. Without running rich, your cat can't reduce NOx so not only do you emit more NOx, but the cat heats up and can become brittle and crumble from only oxidizing HC/CO which produces heat.

[Vince-HX]

Originally Posted by ZachUA

I have a 98 civic ex. Does anyone know if it's possible to convert it to a vx without swapping the whole motor? I'm wondering if it's possible to simply replace some of the current motors components and then reprogram the computer so that it has lean burn?

The vx engine, d15z1, is Obd 1 so it may pose more of a problem than its worth.

The hx engine, d16y5, is what you want to get parts from. You should be able to just put the y5 head on your engine and wire in the 5 wire 02 and add a d16y5 ecu. I think you also may need the y5 intake manifold as it has the appropriate EGR stuff. Dont forget the LAF sensor also, I just priced a new one for my engine because i was curious and my cost was $550


So yeah, its much easier to just swap in a whole engine. Its really not as hard as you may think, a good weekend of work is all it takes. Also Vx and Hx swaps go pretty cheap nowadays, my coworker just picked up a vx engine and tranny for $200.

[Vince-HX]

Does anyone know if the Honda engine K20a3 uses leanburn? I know it utilized the same vtec-e technology as vx and hx engine but I havent found any info about lean burn. Using K-pro tuning software I'm sure you could lean it out quite a bit pretty effectively.

The usa civic si models also came with a dual stage intake manifold, really neat stuff

[justpassntime]

It is so much easier if your car has a atmospheric or barometric pressure sensor.

This sensor, depending on what your particular manufacturer calls it, controls the fuel mixture by sensing the ambient pressure at what ever altitude you are driving. The higher the altitude the leaner the fuel mixture.

All you do is put a 25k potentiometer switch on it and turn it down till the idle speed changes. All you are doing is telling the ECU you are driving at a higher altitude than you really are. There are no problems with warning lights or ecu problems this way.

Just be cautious you don't do to far or you can burn pistons or valves due to higher cylinder temperatures.

[computerpc101]

I have an old 89 Civic Wagon 5 sp, I would like to modify it and run it slightly lean. I have 3 pin PA sensor, One end/centre pin measure about 3K, other end/centre pin measure about 5K, Would you tell me more about how that how I connect those potentiometer?

Thanks

Originally Posted by justpassntime

It is so much easier if your car has a atmospheric or barometric pressure sensor.

This sensor, depending on what your particular manufacturer calls it, controls the fuel mixture by sensing the ambient pressure at what ever altitude you are driving. The higher the altitude the leaner the fuel mixture.

All you do is put a 25k potentiometer switch on it and turn it down till the idle speed changes. All you are doing is telling the ECU you are driving at a higher altitude than you really are. There are no problems with warning lights or ecu problems this way.

Just be cautious you don't do to far or you can burn pistons or valves due to higher cylinder temperatures.