map sensor adjust for use with hydroxy gas

SgtWookie

Joined Jul 17, 2007
22,230
In order to do a good job of adjusting your fuel/air ratio, you'll really need to use the newer type O2 sensors, and develop an interface circuit to "fool" the existing ECU by sending signals that are of highly similar voltage levels to the old-style O2 sensor.

Have a look at this page:
http://www.superchevy.com/technical...cessories_electronics/0407sc_bosch/index.html
It does a pretty good job of explaining how the two basic types of O2 sensors work.

What you have at the moment just isn't going to work well at all. Basically, it's going to delay the ECU's response by some pseudo-random factor, so the air/fuel ratio will be cycling radically up and down.

If the O2 sensor were the newer type, you could actually "tweak" the air/fuel ratio. However, if you mis-adjust things, you will either waste a lot of fuel, or risk severe engine damage due to detonation, burned valves, burned/broken pistons and rings, etc.
 
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beenthere

Joined Apr 20, 2004
15,819
Strongly agree with SgtWookie. The LM3914 fudge will have the signal oscillating between too lean and too rich. A circuit with a couple of op amps that will let you adjust the O2 sensor signal by a small amount and not lose the change occurring from a change in load.

At a constant power setting and load, it is possible to lean out the mixture for economy, but the load has to be relatively light. Some people have done research into this involving aircraft engines. Pushing up power with a lean mixture will burn valves and piston crowns.
 

Thread Starter

gary74

Joined Sep 1, 2008
26
i do know that the circuit moves up and down.. when it does so does the signal out on the led side of the chip.. if it diminishes past .49 volts it is supposed to cut off the out put. When each pin is 50milivolts searated then it will be made to adjust thru a selctor switch how lean you want to operate the carbaration... If you have the time want to read the entire thing.. it is several pages.. i will send you a copy. i have been playing with this dang chip all day trying to figurte how it is set up.. I tried to read the data sheet.. but it is a bit above me.. If I knew that say pin seven controlled the limit of the internal voltage and it had to be maintained somewhere and that the output was controlled by another pin and had to have an amperage input of xI.. then i could figure a bit of it.. but it seems a bit aloof without a teacher.. i am searching for a chip tutorial .. just so far i can't seem to find any that are free. If I could understand the chips ability and then how to make it do what it can do.. then maybe i could figure is the rest of the circuit working.. but i am sweating now.. too long in this chair
 

SgtWookie

Joined Jul 17, 2007
22,230
You can download the datasheet for the LM3914 from National Semiconductor's site. It has numerous examples of how to set it up for use with LED displays. It's resolution can go as low as 50mV per division.

However, your big problem right now is that you have the wrong kind of O2 sensor to even have a chance of making this "kludge" LM3914 circuit work. It requires the later style of O2 sensor. You have said yourself that you have the early type.

The way this kludge is supposed to work is taking a linear input signal from one of the newer type O2 sensors, and toggle the output up and down to approximate a DC voltage level. It's pretty coarse.

However, your O2 sensor is either near 0V or near 0.9v. It won't hover at midrange; it shoots right by the midrange levels. The newer type of O2 sensors only started appearing on cars over the last decade.
 

thingmaker3

Joined May 16, 2005
5,083
The adjustment provided by VR1 makes no sense to me. Pin 7 generates a 1.25V reference, as has already been noted by the Wookie. I see no purpose or reason for the 1K resistor between pin 7 and ground. VR1 to changes the reference voltage on pin 6 by virtue of the internal resistors in the window comparator. Voltage on pin 6 will be between 0.417V and 0.833V.

If the i/p from the O2 sensor is digital, as has been claimed, the adjustment does nothing.

The selector switch also makes no sense to me, since o/p of the bargraph driver will be either all dark or all bright.

I also wonder how much engine electrical noise will degrade the performance (if any) of this thing - it has no signal conditioning on the i/p.
 

Papabravo

Joined Feb 24, 2006
21,159
This conversation is not about technology, but about religion. It is impossible to convince the faithful that they have in their infinite wisdom, been hornswoggled by scammers once again. You guys are wasting your breath.
 

Thread Starter

gary74

Joined Sep 1, 2008
26
hey guys.. I am looking into buying a newer type of O2 sensor... i thinnk you for the consideration and i am trying to restudy a lot of electronics... I hate when i get as the religion expert says.. hornswaggled.. but i have been.. I do make a lot of hydrogen and I know that it does help that deisel run lots better on the generator.. i read some other articles and am reading the one sgt listed for me. .. thanks a ton guys again...
 

SgtWookie

Joined Jul 17, 2007
22,230
I don't know how I missed it initially - after all, it's the title of the thread.

It says "map sensor adjust for use with hydroxy gas"

You can't use the MAP sensor of a narrow-band (old type) O2 equipped vehicle to "tweak" the fuel/air ratio in closed-loop mode; it will cause the ECU to be running in open-loop mode instead.

Along with changing the O2 sensor to a newer-type wideband O2 sensor, you will need to monitor the temperature of your catalytic converter. Don't let it get more than about 100°C hotter than it's getting right now, or you may find yourself having a catastrophic converter failure (read: very hot fire under the car) that will very quickly lead to your vehicle being completely destroyed.
 

Null_THD

Joined Sep 19, 2008
2
Hey guys, this is LITERALLY my first post on this site ever. I joined, opened this thread and since I have some ongoing interests with this too, I figured I'd submit. Anyway, I whipped up an 02 sensor adjuster circuit, however it's very very rough. Basically it just allows you to add a positive offset to the signal.

Anyway, here it is:
 

SgtWookie

Joined Jul 17, 2007
22,230
It didn't post properly, but here it is:



The text is too small for me to be able to read it. Any chance you could make it a slightly larger size?
 
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