air fuel ratio questions...

[HPR]

I just noticed under WOT my air/fuel gauge shows stoich. Am I supposed to hit the green rich area? If so, what could be wrong or can I do to fix it? If that's the way its supposed to be, then cool...

Also, is there any way to convert to a 4 wire o2 sensor from my 1 wire? Are there any benefits in doing so? Because for my prelude I went from my original 2 wire to a 4 wire from a newer honda and my air/fuel gauge responds A LOT faster than before.

Anyways, sorry for all the newbie questions. Just trying to learn something new

[Flashmn]

In Wot condition you should be on the rich side of the scale I think, not sure how EFI does these things tho.

Also, is there any way to convert to a 4 wire o2 sensor from my 1 wire? Are there any benefits in doing so? Because for my prelude I went from my original 2 wire to a 4 wire from a newer honda and my air/fuel gauge responds A LOT faster than before.

Yeah there is. You just need to know where to plug the heating cords. The reason it responds faster is that the sensor is heated to the operational temperature.

[Punisher]

Under WOT it should go lean.. when you start the engine it should hit rich.. otherwise it should be bouncing between first bit of rich and first bit of lean under cruise.. pulsing basically.
I am putting an LED AFM gauge on my rolla soon as I get back from vacation monday night.. help me to tune the carb a lot easier.

[Flashmn]

Under WOT it should go lean

UNDER WOT IT SHOULD NOT GO LEAN. If it does it might start detonating and goodbye engine.

[Punisher]

Really? I was told that it should go lean

bah.. so it should go rich...?

[Flashmn]

Yep should go rich.

[HPR]

from what I know it should be rich as well... does anyone happen to know if temperature and humidity happen to affect air/fuel ratio? because it averages around -10 here and since its really dry too, the colder air is a lot denser. just a thought.

[Flashmn]

Yeah it would affect it, but if you got EFI the computer would adjust to compensate. Factory carbs are set to run in different conditions, so no worries there either (I guess).

[AngryAE101]

Hey guys wassup,

I saw surfing and saw this thread and just wanted to hook ya up. This is an exerpt from the SDS efi website. Its talking about almost the same meter you guys might be using. It also explains Air fuel ratios and how that is.

Tuning with a Cyberdyne Mixture Meter

06/16/99

This article guides you through the process of tuning an SDS unit with MAP sensor, using the Cyberdyne mixture meter. The meter is useful in determining the APPROXIMATE air/fuel ratio at any given point of operating conditions.

Background Information

The mixture meter is essentially a digital LED voltmeter reading the voltage produced by a standard oxygen sensor. The voltage ranges from around .9 to 1.0 volts when the mixture is rich at 12 to 1 air to fuel ratios to 0.1 volts when lean at 17 to 1 AFRs on gasoline. The meter can be used with alcohol fuels as well but cannot be used with leaded fuels.

Spark ignited engines will produce the desired performance only within a relatively narrow range of AFRs. Best power is usually obtained with an AFR of between 11.8 and 13.0 on most engines. The lowest average emissions are obtained with the AFR around 14.7 to 1 (stoichiometric) and best fuel economy is at AFRs between 16 and 18 to 1. Most engines do not idle happily unless they are setup to run richer than 14 to 1 AFR. You can check the AFR vs. LED sheet supplied with your meter to get an idea of what AFR you are running at. The basics are shown below:


RICH----------------------------STOICHIOMETRIC-------------------------LEAN

To get the best compromise programming setup for your application, you will have to decide which areas are of most importance. If you have a race engine, usually fuel economy and emissions are of less importance than maximum power so you can setup the AFRs to be around 12 to 1 everywhere. On a performance street engine, both power and economy are usually important and emissions may be as well.

Tuning may be done on a dyno or driving the vehicle. Dyno tuning is preferable when maximum power is paramount as this allows the quantitive measurement of increases or decreases due to both ignition timing and air to fuel ratio changes. Fuel economy and throttle response parameters are best tuned by driving the car on the road and most street cars can be safely tuned on the street with the aid of the meter. It is important to understand that the engine should never be leaned out at high rpm or high throttle opening or boost conditions. This can lead to overheated and damaged parts or complete destruction if preignition/detonation occurs.

Base tuning should always be accomplished with the Closed Loop function turned OFF. When the system is in closed loop, the ECU looks at oxygen sensor voltage to correct the air/fuel ratio automatically to around 14.7 to 1. This is mainly for emissions. It is dangerous to run most engines hard in closed loop mode because the air/fuel ratio is too lean at high hp levels. For the purposes of simplification, we will assume that the closed loop function may be used for the part throttle conditions to satisfy emission requirements only. If emissions are not a concern, better driveability and fuel economy is often obtained by leaving the system in open loop or programmed mode under all conditions. Open loop mode is when the system is operating off the values programmed into the ECU's memory.

Several things are important to observe during the tuning process:

1. Let the engine reach full operating temperature before changing any MAP, TP or RPM values. If you try reprogramming while the ECU is still adding extra fuel for warmup, you are wasting your time and getting off track.
2.You must vary only one parameter at a time and observe the meter. If you change rpm and MAP, you don't know which parameter is affecting the air/fuel ratio. Hold MAP constant and vary rpm or vice versa, never both.
3. Make absolutely sure that fuel pressure is staying where it should, that all injectors flow the same volume, have good patterns and that injectors and pumps have sufficient flow rates to feed your engine at full power. No amount of programming will fix inadequate fuel flow caused by a mechanical problem.

Tuning Idle Mixture and Initial Setup

Turn the mixture knob after starting the engine to obtain a smooth idle. Let the water temperature reach 50C or 120F. If the knob is set leaner than 0% for a smooth idle, it means that the RPM FUEL value is too high at that idle rpm. For example, suppose that the engine is idling at 1000 rpm with the mixture knob at -12%. The RPM FUEL value at 1000 rpm is 80. Hit the -1 button on the programmer a few times until you can turn the mixture knob back to 0%. We'll say that you have a 70 now for an RPM FUEL value at 1000 rpm. You can now try slowly decreasing the value by ones until the engine becomes a bit rough. Note that value, we'll say it is 66. Now increase the value slowly by ones until the engine gets rough again. We'll say that this happens at 77. You now know that the engine is pretty happy with the RPM Fuel 1000 value in the middle of these two extremes at 70. This is a good starting point for all of the RPM Fuel values right up to redline. Make them all the same, (70 in our example).

If you notice that the idle speed fluctuates up and down slightly, go to gauge 1 mode and look at the MAP window. You will likely see it moving between several ranges. Note the highest and lowest ranges. Go to those ranges in the Manifold Pressures and make all values within those ranges the same, about 30 in most cases will work well. This should smooth out the idle. Once the O2 sensor is warmed up to over 600F, it should supply accurate voltage readings to the mixture meter. You will probably notice that your engine idles the smoothest when the mixture is fairly rich. This is normal.

Dyno Mapping

Whether you use a chassis or engine dyno, we have found the easiest way to tune is to do a baseline run with the mixture knob at 0%. On turbo engines, turn the boost for initial runs to the minimum possible. Back out of the throttle if the meter shows a bad lean condition or if any severe misses are encountered. If the engine will make it up to redline on the baseline run, do the next pull at +10% on the knob. You can now superimpose the two torque curves to see where you picked up or lost torque due to the richer mixture. Keep richening the mixture in 10% increments until torque drops off from the previous run. Note where in the curve that the gains and losses were evident. Now you can fix the peaks and valleys with the programmer and return the knob to 0% for some stabilized pulls. For quick, full throttle setup, load up the engine at each 1000 rpm break point and keep richening the mixture at that rpm point with the programmer until torque starts to fall off. Adjust for maximum torque at each point. Fill in the 250 rpm steps between each 1000 rpm point with a smooth transition of values.

Once the engine is tuned well at full throttle/low boost conditions, the boost may be slowly upped. Any lean condition now at the higher boost as indicated by the mixture meter or a loss of torque can likley be attributed to improper MAP values. By looking in Gauge 1 mode at the MAP window, you can see where the ECU is currently operating and adjust that range if needed. These should be adjusted until the meter stays in the red rich zone and for maximum torque. Part throttle and accelerator pump settings can be done on a dyno but are probably better set on the road.

On the Road Mapping

You should select a stretch of smooth straight road with a few long hills if possible. The hills will allow you time to stabilize conditions at higher throttle openings without getting way over the speed limit or roasting your brakes.

It is usually best to begin with full throttle, low rpm conditions first. On turbo cars, turn the boost pressure down to the minimum possible. RPM values should be adjusted first. By doing these at wide open throttle, you are only changing one thing at a time which allows you to adjust the correct parameter (rpm in this case). Put the car in 4th or 5th gear at 2000 rpm and floor it. Watch your mixture meter and tach or rpm in gauge 1 mode. You want the mixture to be rich at full throttle, usually in the upper yellow or lower red as shown below.

If the meter reads fine until 5000 rpm and then leans out there, you can punch up the RPM FUEL value by 10 at the 5000 rpm range and try it again. Note that you can flick quickly between gauge 1 and the range that you are programming by just hitting the Gauge button again. This saves a lot of scrolling.

Once you get the mixture correct at full throttle throughout the whole rpm range, you can turn up the boost and start on the MAP values. If the engine ran fine to 7000rpm and 2 psi before but now leans out at 10 psi and 7000 rpm, you must increase the MAP value at 10 psi. Again, you should be in gauge 1 mode watching the MAP and your mixture meter for any signs of lean out and at what MAP it occurs at. Use a hill and brakes to stabilize conditions for a few seconds to verify the bad range.

Part Throttle and Cruising

The part throttle conditions are probably the hardest to set up. Under light load conditions, you want the mixture to be substantially leaner than it is at full throttle. Depending on the engine, you want the mixture to be at least around the middle green LEDs as shown below:


Some engines are quite happy running full lean on the meter as below:


Many engines will actually cruise smoothly at very lean mixtures which are right off the lean end of the meter with no LEDs lit. If the engine starts to miss or the car hitches as you lean out at part throttle, the mixture is too lean to be tolerated. Most adjustments are done to the MAP values for cruising conditions.

[AngryAE101]

What dose this mean???????? well what Airfuel ratio is is the actual mixture that is introduced into the cylinders for combustion. Perfect chemical mixture for combustion is 15:1, 15 pounds of air to one pound of fuel. For automotive engines 14.7:1 is the perfect stioch ratio for "fuel economy". Notice i put fuel economy in quotes. at half throttle running stoich is the best thing for economy and drivability. This is acomplished in stock efi or stock ecu"s with the 02 sensor hooked up to your exaust system. It reads what oxygen is left in the exaust after combustion and with that determins the AFR in closed loop mode. Now lets us think about that.....................................fuel economy and power ARE NOT COMPATIBLE WITH EACH OTHER ! an afr at WOT of stoich wich is 14.7: 1 is extreamly dangerous . That is a really bad lean out condition which skyrockets egt and melts your beloved pistons. What dose that mean??????? Dead engine. if you would look at an actual AFR gauge with lights running inbetween stioch and the richest point is where most power is safely made at WOT. It gose 16to1(lean) 15to1, 14.7to1(stioch)
13to1(minimum afr at WOT . Full built high VE NA engines survive this) 12to1(lean power zone) 11to1(perfect for turbo power zone) 10to1(rich power zone for really high boost and IGN timing safe) 9to1(rich starts loosing power but still safe) 8to1(rich....black smoke , power loss but safe) . write these down on a graph and u will have the map you need for understanding AFR and what the numbers mean . Yes runnig lean makes power but its it very dangerous , and running rich makes less power but is safe. What you have to do is find where your engine makes the most power and keeps the knock down and EGT's lower than 950celcius on a egt gauge . Only on a brake dyno can you find the sweet spot or with the use of a Gtech pro(sweet toy good for mesurement of acceleration and power bands). What i tune cars to usually turbo is inbetween 10to1 and 13to1 AFR . if you can get that kind of AFR at WOT across the whole rpm band you will make your engine into a very angry motor that will treat you to some good pulls on hondas An example of the importance of tuning to the right AFR is what happend to me and my friend yesterday at the dyno. He owns a nissan 180sx with a CA18 turbo motor. The motor comes stock with around 170rwhp and counting on his being old he probly had less. For mods all we had was No airflow meter because we installed a standalone which eliminated the AFM and ran MAP sensor , exaust with aftermarket downpipe and no cat and a boost controller. We only had money for two runs so i used the first to look at the AFR and datalog all sensors and guages. We put down 169.1 rwhp at 12psi of boost. The stock boost it at 10 psi roughly . During the run i saw it leaned out at high RPM so from 5000Rpm and up i richened the fuel up to 11to1 afr all across the RPM band . with the same boost and more fuel we dropped down 210rwhp ! Dam? what good tuning can achieve. he was a happy man that night at the street races pulling wayyyyyyy harder and faster. THe AFR gauge we use is the greddy AFR gauge . Its a narrow band that is really close to a wideband or profesional AFR gauge. It is well worth the money if you are serious about making power because it actually says the AFR number on it and not no little light that can throw you off. I do not recomend the autometer or any other exept the greddy or anything wideband. Geddy AFR gauge is priced around 200 dollors and comes with 02 sensor and is full electronic with its own computerized controller/ data unit. Hope this helps

[Flashmn]

if you want one of those led light AF meters, just make your own, its really simple and cheap

[HPR]

great stuff... very interesting read. I'll see if I can apply what I just read into physical work.

[AngryAE101]

hell yea man , just try it for your self and good luck. Hope it helps.