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Old 10-18-2007, 02:44 PM   #11
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Ok lets reconsider this, a VX o2 sensor is a wideband, thus it does take the inputs in differently, rather than a narrow band.

Ok NOW, your going to be telling your ecu your running rich all the time. Your o2 is not your only form of a/f to the computer. An obd1 computer has a set map every time you start your car, it basis your fueling by 1st your map and tps sensor, then immediately (mostly when its cold) by your iac valve, which causes fast idle, when you start your car on a cold day it leans the **** out of your fuel mixture to increase warm up time, most obd - obd2 cars are set up this way.

By you fooling the ecu into thinking its rich all the time, will potentially damage your engine. Your a/f through the rpm range at different throttle posistions is not consistently rich, no way no how.

So say at 3500 with 40% throttle your running a bit lean, by you changing your o2 to constantly lie you will go to a dangerous lean level. Just leaning out your o2 will temporarily help your fuel mileage, but will cause long term damage, I can promise you that.

By telling your car you are running rich all the time it will advance the ignition (this is natural, this keeps the car from loading up) once that happens and you at the given RPM you are running lean you will have a mis-fire or post fire. In no way shape or form would I ever do something like this without a way to fine tune it. When leaning your fuel supply you should also retard your ignition, you should have a way to alter your map/maf sensor inputs.

If you want to save fuel, your best bet is to find a chip that includes a data port for a laptop, you should have a wideband o2, a laptop, and datalog in real time the inputs of all your sensors, and tune your ecu with your laptop accordingly.

An engine is MOST efficient in every single way is 14.7:1, however, that is speculation, I've heard an engine is at its highest performance peak at !3.9:1, if an engine is at its peak performance, its fuel economy will be at its highest performance.

I'm just saying, lying about 1 single sensor to alter fuel with no exact a/f ratio, its not a good thing.


I understand that in a seriously lean situation the o2 will actually send a lean signal to the computer, but your going to have so many peaks and valleys in your a/f curve that the engine will become choppy, it will loose power and gain power at certain rpm's and throttle positions. I understand that this is all for saving $$$$ but in the long run, is saving $20 bucks every six months worth the damage that you take the risk of causing upon your engine? The chance of blowing a ring land, the cost of ruined plugs? This is why fuel management systems are so expensive, their ability to alter a signal of MANY sensors at the same time having the ability to be variable, by rpm and throttle position.
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Old 10-18-2007, 02:52 PM   #12
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If I remember correctly, the wideband puts out a low volatge when it is rich, so you should be able to put in a high ohm potentiometer as a voltage divider to lower the voltage output so the computer thinks it is running rich and leans out the mixture.

If you want to richen the mixture then you need to amplify the signal.

If I remember correctly.
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Old 10-18-2007, 02:58 PM   #13
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Yikes...the only time I might see this to be useful for me, is possibly on cold starts where rich is the name of the game. The cat gets hot fast, so why so rich???

I'm quite concerned about running lean, and consequent internal engine wear, so bear with my alternative proposal.

So, if this system could be switched to force a closed-loop and O2 sensor offset shortly after startup, would the inefficiency be reduced, but retain engine longevity? Of course once the vehicle is warmed, a bypass directly to the stock closed-loop system would be required to go back to "normal". So much fuel is burned on cold starts, and driving warmup...

Any thoughts?
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Old 10-18-2007, 03:21 PM   #14
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That doesn't make sense to me, on initial start up yes you would be dumping fuel, however, the computer should lean your fueling out to create heat, running rich will create your engine to run cooler, running lean creates alot! of heat! As far as everything I've read and monitoring a/f after initial start up the engine leans out to create heat, and thus warm the engine up quicker. Post cat o2's mostly monitor cat heat, which would be a lean situation, running rich will not cause near the heat as running lean will.


Internal wear is not an immediate issue, unless the a/f rose 18-20:1 and then damage, mostly from heat and mis-fires would occur.


I have not done a ton of research in the differences between closed loop and open loop, i understand the difference, but do not know exactly what engine functions are changed and what sensors are used as primary and what ones aren't. I know in warm up, your a/f is based off of the IAC valve on a Honda, that and a few others, but that controls the amount of air going into the engine, and when that sensor is switched off the fuel mixture richen.

Actually the fuel is never really cut, it allows more air to bypass the throttle body, allowing for a lean situation, thus creating heat, and then warming your engine up quicker. Cutting fuel to an engine is not always safe, Honda tuned their engines to work properly at all temps, and altitudes, by faking the o2 to the computer and not changing anything else could be harmful......
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Old 10-18-2007, 03:24 PM   #15
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Old 10-18-2007, 03:27 PM   #16
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I am also NOT saying that long term engine damage WILL occur, I'm just simply stating that you will be walking the fine line of long term damage. The same goes for over fueling as well, causing pre-det, or pinging. There are so many variables that have an effect on a/f besides just the o2. I guess I'm just pretty picky on what I do to my car as though. Basically, if you can increase airflow to and from the engine (hopefully keeping it quiet) and keeping good back pressure, and then lean your engine out, your efficiency will increase alot! More unused power means less engine effort and less fuel used. Don't believe me, how do cummins desiels make 1400fptq and get 2+ miles per gallon better than stock? Because they have less load on the engine itself. Or ok, thats wrong, the same load, but the engine is only working at way less capacity than with less power.


I can't explain things, I wish I could explain better, but I pretty much suck at it.
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Old 10-18-2007, 03:34 PM   #17
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Having a small background in tuning, it is my gut to say not to do it, because not only do you not really know what you're doing changing it, you don't know what X changes will actually do to the car. It's like taking a shot in the dark and then not being able to turn the lights on to see if you even hit anything.

Besides, emissions increases from running lean are t3h suck.
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Old 10-18-2007, 04:15 PM   #18
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Quote:
Originally Posted by MY02WRX View Post
That doesn't make sense to me, on initial start up yes you would be dumping fuel, however, the computer should lean your fueling out to create heat, running rich will create your engine to run cooler, running lean creates alot! of heat! As far as everything I've read and monitoring a/f after initial start up the engine leans out to create heat, and thus warm the engine up quicker.
All newer cars I've heard of run deliberately rich on startup to light off the cat quickly. Emissions and all that.
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Old 10-18-2007, 04:54 PM   #19
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What about the VX lean burn mode? Is that harming the engine?

I would like to lean out my carburated 87 civic, but I too am concerned about engine damage.

I can tell that the engine sometimes runs a little richer and other times leaner (I suppose the crude electronic control box is trying to do its job). Sometimes when fully warm, I get a little spark knock climbing a hill on my way to/from work, other times, I get no spark knock on the same hill, even when I purposely lug the engine a little and when it the same outside temp and same engine temp.

By the way, is there anyone out here that knows how the honda feedback carbs richen/lean the mixture? It is not electronic (I have rebuilt the carb) so it must be a vacuum bleed to lean it out or somehow keeping the power valve from richening the mixture via a vacuum line.
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Old 10-18-2007, 05:09 PM   #20
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also running lean from cold just doesn't work- stumbing, hesitation, dieing and all that. needsta be warm enuf ta vaporize afor switching to lean
So is that the main reason for the ramped-up operation on cold starts?

I want to understand why. According to the shop manual, coolant temp determines idle speed via the IAC valve (on a modified S-like curve).

I want to minimize emissions, but at the same time minimize fuel consumption -- am I asking of a tall request of a modern ICE? On cold starts, I can shift the gear selector to '2' and idle along at 20-25 mph. 2500 RPM is the magic number to shift the auto into higher gears when cold -- that sucks (fuel...literally).

Let's say the coolant mod is introduced. Can I expect rough idle, and possible a stall on a shift into 'D'? Is this something you have to live with, and rely on the grille block to keep things toasty???

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