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Separate Loads turn off and turn on delay

Discussion in 'General Electronics Discussion' started by arg733, Feb 28, 2013.

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  1. arg733


    Dec 14, 2010
    I need an (adjustable) time delay circuit that will delay turn off to a load and delay turn on to another load. Space is not a big issue.

    APPLICATION (not necessary to read)

    Actually it's kind off funny.
    I have a four cylinder injector car that also shows instant and average fuel consumption (among other things) and i noticed that if i shift down (i have manual transmission) while i go downhill the revs go up (naturally) and the fuel consumption gradually decreases until it drops down to 0.0 L/100khm !!! LOL? (so the injectors are completely turned off)

    Now after a lot of thinking i finely understood that behavior and i will try to explain it.
    So when i release the throttle it is if i'm telling the computer that i need the engine's rpms to go to idle but it can't go there because i have the 3rd gear in (just an example) and the wheels are making the engine go some 5000rpms so it tries to bring that 5000 to idle (800rpm) and it's trying to do so by decreasing the fuel and as there is no minimum value it goes all the way down to 0 ?

    So i thought to switch the cylinders fuel injectors, off manually, and not wait for the computer to do so. I can also drive with only 3 or 2 or even 1 cylinder instead of 4 when i don't need the horsepower.

    The problem is that if use simple switches to switch the injectors off, the sparks plugs will still be running and produce ozone (o3) which can cause damage to the exhaust as it is a better oxidant that oxygen (o2), so i will need to turn the spark plugs off also. This creates another problem : If i turn off the injectors and the sparks simultaneously there will be always some fuel left unburned that will destroy my catalytic converter.
    That's where time delay comes in : i will turn off the switch which will cut power from the injector and the circuit will wait 200msec and then cut power from the spark plug to ensure that all of the remaining fuel in the intake and the cylinder is burned out.
    When i will turn on the switch it would work in reverse: first the spark plug will turn on and then after 200msec the injector will turn on to ensure that the spark plug will already have power when the injector powers on and sends the fuel in the combustion chamber.

    Oh and i made a road test with 3 cylinders (i unplugged 1 injector) and another with 2 cylinders (i unplugged 2 injectors). The car was going nice, I couldn't notice a big difference with 3 cylinders just that it took a little longer to accelerate and with only 2 cylinders i had to shift down a gear to climb a hill, so i know it works fine other than the annoying "Engine Fault" message and the "check engine" light going on (both went off after i reconnected all the injectors), another side effect was that the computer stopped measuring the fuel consumption (i can calculate it, no problem) and ignored all readings from the oxygen sensors and went to the factory default air/fuel mixture ratio (i sawed that with an obd2 scanner while driving).

    Thank you very much.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The basic thing is that when you disconnect stuff the computer recognises that stuff isn't quite right and goes into "limp home mode"

    Yes, it is quite possible that the computer turns off fuel to the engine when you're coasting down a hill. It has been observed a lot. Indeed it is a recommendation by "hypermilers" to *not* put your foot on the clutch as you descend a hill because doing so may actually use more fuel.
  3. arg733


    Dec 14, 2010
    Heh, my car isn't that advanced though, it can't recognize if all the injectors are running or not it only has a sensor on the crankshaft. I tried to read the fault codes with the obd2 scanner and it appears that the computer thinks that there is "Multiple cylinder misfire" even if i have 3 cylinders running.

    You are correct if i switch to neutral and i have a speed of 100km/hr the consumption goes to about 2lt / 100km
    I also tried to switch ignition off (with the key) and it had no effect , i could not hear any change in the sound of the engine. When i switched on the key again ,when the road started to straight off, it kicked in immediately, i didn't had to run the started again as the engine was already rotating.
    Last edited by a moderator: Mar 1, 2013
  4. duke37


    Jan 9, 2011
    Many years ago London Transport tried reducing the number of active cylinders on their diesel buses when the full power was not required. The differential thermal expansion harmed the engine.
    I believe that the inactive cylinders were later cycled but I never heard the result of the experiment or the fuel savings obtained.
  5. arg733


    Dec 14, 2010
    I found a way around the delay problem, i will just use an off-on-on switch.
    I also thought of making it a little more automatic. Can i use a sensor (orientation sensor or angle sensor???) that will sense if i am going uphills or downhills and turn on or off the cylinders?
    Last edited: Mar 8, 2013
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