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Old 05-23-2005, 09:22 PM
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O2 fuel injection and simplicity

I've been thinking a little bit about trying to make a VERY simple home built fuel injection system.

With advances in technology some things that were once thought impossible can now be acheived. With the newer preheated O2 sensors I think it may be possible to make a simple fuel injection system.

It would be as simple as having an O2 sensor, fuel pump, injectors, "relay switch" and solenoid operated bypass valve. The "relay switch" should be rather simple to build but i'm not up on electronics enough to know how. I do know that it can either be a normally open or normally closed switch due to the simplicity of this idea. I do know that it must operate at .3v to .6v and needs to have a "power swith" preferably operated off vacuum. I have most of it figuered out if anybody can help me make the switch.

I have a little diagram drawn up also.

So really my two questions are:
1) how fast does an O2 sensor respond to changes in the fuel ratio?
&
2) Can anybody make a 3 way switch that will ground when the sensor voltage reaches .5v?

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Old 05-23-2005, 09:33 PM
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.3 or .6 volts isn't enough. Most domestics run their systems on 5 volts because that is about as low as they could go and still have good control.
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Old 05-23-2005, 09:42 PM
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I've heard 5v myself but this says different. >That is, if the exhaust has 2% oxygen, it is lean. This produces a low voltage, below .3 volt (300 millivolts). If the exhaust has near 0% oxygen, it is rich. This produces a high voltage, above .6 volt (600 millivolts).

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Old 05-23-2005, 09:49 PM
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This is true. That is the signal the O2 sensor creates but it isn't enough to power anything, it is just a signal to the ecm which controls everything through the basic 5 volt reference,
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Old 05-23-2005, 09:54 PM
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Recall

I saw a simple fuel injection system a few years ago that seemed to work just fine..it read the throttle opening the mass air flow and engine temp and there was a fuel curve plotted from thos requirements..

used a small computer to plot the fuel curve and adjust the fuel accordingly..I think it used ford or bosch injectors and the one I saw was adapted to an ordinary cast iron manifold..

Something like that might be doable with some thought and research..Once a guy got it to work then go for the better manifolding and such..

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Old 05-23-2005, 09:57 PM
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I'm not sure if it would even run, if I"m understanding how you would want to make it. Generally to get the car started you need an extra rich shot, or when its cold etc. Also, you're only measuring one variable, which is the same thing a carb does, so I'm not sure if it would be a great plan. Maybe for like a lawnmower or something it woudl be cool-

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Old 05-23-2005, 10:50 PM
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Seems like what your talking about would be harder to setup than a "complex" fuel injection system. I have a hard time seeing how this would even work. I can see how you might get it to actually inject fuel, but what are you going to use to measure how MUCH fuel you need for the given amount of throttle. I just cant see how this "simple" system works. Even if you could get the amount of fuel to respond in accordance with what the 02 sees, it still wont be able to account for quick changes in throttle position, or temperature or anything of that nature. You might get decent gradual throttle response but with quick jolts of acceleration you'll undoubtably get lean pops.

Why not pick up a used TPI or something off ebay and set that up?
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Old 05-23-2005, 11:20 PM
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Read this

click here Those people who ran Hilborn or Enderle in the old days can relate to what is needed to make an engine run..

The modern EFI is a whole new deal which has to work seamlessly in a grocery getter for Mom and pass the emissions rules..hence there are a lot more sensors to make it do so..

If an injection system is on a race car or offroad we can get by with measuring the bare minimums necesary to make the thing run and build power..soooo one can look at that and design accordingly....

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Old 05-23-2005, 11:56 PM
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Those sensors that are in the grocery getters for the emissions regulations and whatnot are there for the reason of efficiency. While yes, you can get an engine to run with less, I beleive that the more "complex" FI engines have the potential to make more power (and more MPG) than any of the simpler systems.

This can be seen in tuners attemps to maximize power, but using each of those sensors to customize fuel and spark tables to maximize their engines efficiency.

Add that to a complex systems ability to adapt to the environment (temperature changes, altitude changes etc) and think you'll find that you have the capacity to make more power in ANY environment.

Like was said, you can get by with less, but that does not mean you'll make more power (or even equal power) with less.
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Old 05-24-2005, 05:46 AM
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It seems to me that if the relay was transistor operated instead of a mechanical relay like i have in the pic that part would be virtually instintaneous.

The O2 sensor i was asking how long it took to respond to changes in the intake tract. and that's why i said a vacuum power circuit would be needed. ie the instant vac. dropped it would give an instant jolt of fuel.

and part of the idea is that the injectors would be like boosters with small holes. the booster can vaporise fuel droplets, think how much vaporization couls be acheived if this booster was vaporizing a mist squirting from it!

It seems to me it would be cheap and effective, as long as the hype about O2 sensors being accurate and quick responding are true. Also with this mechanical injector the higher pressures could be used to allow for better atomization.

The only problems i see are that the O2 sensor would have to warm up for 3 mins before starting and i don't know how to build my electronic relay..
.
.
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Old 05-24-2005, 06:27 AM
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Well, don't give up on it but it does need some refining. As mentioned you really need more input than just O2 like MAP (BMAP) throttle position, temp ect. Hollry's early projection tried to do it with just three inputs and those never ran very well. Also normal O2 sensors actuall run 0-.9 volts and many tuners consider them limited and used a broad band O2 sensor that can read a much broader band.
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Old 05-24-2005, 06:31 AM
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your first problem would be getting the car started under any condition other than "just got done running." Your system wont understand that a rich condition is desired for starting the car, because the velocity of airflow is so low (and sometimes the ambient temp) that a normal amount of fuel is insufficient to atomize in proper quantities. Some kind of mechanical choke system could fix that (or if it were just going to be a lawnmower you coudl "prime" it). The second thing that would be a problem would be quick throttle changes. THe system would spit and pop as the engine transitioned. You simply cannot have a quick transition read post-hoc like that. In a normal fuel injection system the TPS measures the distance change over time of the throttle, and an accelerator pump takes care of this for a carburetor so that the engine gets the fuel at the same time as the rush of air, not after it reads that its lean.

Like I said, it would be cool for a lawnmower or something that doesn't change RPM very often-

K
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Old 05-24-2005, 06:34 AM
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Quote:
Originally Posted by killerformula
THe system would spit and pop as the engine transitioned. You simply cannot have a quick transition read post-hoc like that.
ah, that's what i was wondering. too bad ...looks like i'm going to have to use a TBI box if i want to do this.
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Old 05-24-2005, 11:33 AM
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Not to gripe but this was also mentioned in my first post .

In the programming for the more complex fuel injection systems there is actual code and tables for a "pumpshot" based on throttle changes. It allows you to dictate the amount of fuel added, as well as how long it takes to decay out.
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Old 05-24-2005, 11:48 AM
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I think it's great that you are giving your brain a real work out. And maybe you could get it to work ok too. You need to use a heated o2 sensor and have it close to the engine. I think it will need a lot of thought.

You may want to give the megasquirt dyi efi forum a look. It's is a great system. especially for the money. You can use a lot of junkyard parts to build your system.
http://msefi.com./
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