Theory of operation

[dray0151]

I think I went out with a girl like that once.......

You didn't keep her? Sounds pretty good!

[jackmanjls]

ausnoelm...the quest is not to know what the "air temp sensor" monitors as much as how the ECU uses the information to monitor air density and determine the air/fuel mixture.

Much diff than just the basic definition of "air temp sensor".

All the inputs are fairly self explanatory but it's how the ECU uses these in the overall process that needs to be understood.

[ausnoelm]

You're way over thinking it, all you need to know (unless you are getting into design or manufacture) is there is a device that determines the air temp, then in a jiffy, the ECU knows how much fuel and air is needed, if the timing needs to be advanced and so on, exactly how it does it is not adjustable by the user, nor is it important to the user or mechanic/technician.

[boscoe99]

ausnoelm...the quest is not to know what the "air temp sensor" monitors as much as how the ECU uses the information to monitor air density and determine the air/fuel mixture.

Much diff than just the basic definition of "air temp sensor".

All the inputs are fairly self explanatory but it's how the ECU uses these in the overall process that needs to be understood.

The engineers have decided how many parts of air that they want mixed with every part of gasoline for a given set of circumstances. You will see 14.7 or so parts of air for every one part of gasoline mentioned quite a bit but that is just one number. Don't pay too much heed to it.

Now keep in mind that air is changing all of the time. It changes with air temperature (air temp sensor input). It changes with the throttle being opened and closed (throttle position sensor input). It changes with the RPM of the motor (tachometer input). It changes due to nature (manifold pressure input). It changes with the temperature of the motor itself (engine temp sensor input).

The engineers are using these sensors and other stuff to try and make a best guess as to how much air in getting into the cylinder each time the cylinder moves downward on the intake stroke, sucking air into the cylinder. Actually, they program the ECU to do the guessing for them. It is real quick. One thousandth of a second (a millisecond) is a short amount of time for you and me. For an ECU it can seem like an eternity.

The ECU looks at all of the inputs that it receives from various sensors and in the blink of an eye (actually less time) it estimates the amount of air going into the cylinder. It then decides how much gasoline should be injected into the motor. It may open a fuel injector for 30 milliseconds in one situation and then open it a tad less or a tad more, depending upon any air changes that it sees.

Also, while all of this is going on the engine takes bit of data available to the ECU and decides when to fire a spark plug.

Some ECU are looking for an input from a knock sensor. Knock is pinging or rattling you might have heard. It can damage a motor. If the ECU senses any knocking it very quickly makes adjustments as needed to make the knocking go away.

Now some motors will uses sensors to measure the air quality (O2 sensor) and/or the temperature of the exhaust gasses (exhaust gas temperature probe). Depending upon what the sensors tell the ECU, the ECU can then make an adjustment to what it was doing, to try and make the situation better. No Yamaha four strokes use an O2 sensor or an exhaust gas temperature sensor.

Here is some theoretical information.

Theory: Speed-Density « Moates Support

Some will say this is all stupidly simple. I don't share that position.

[pstephens46]

Intuitive for some but not all. Including me. I like to learn.

I once complained about Organic Chemistry in college to a friend. A friend who ended up getting a doctorate in chemical engineering. He simply smiled and shook his head.

[dray0151]

Makes you appreciate that little black box on the motor. It may be stupidly simple if all you consider is it takes a signal in and sends out a signal but there is an awesome amount of work it does to get that signal out for you to go scooting down the lake hunting that next big catch!

Thank you Boscoe for your info, I bookmark these for reading just to know what is going on not that I can fix anything but just to understand just a bit more.

I bet somewhere some little Jap engineer has a full library of diagrams and flow charts on how all of these interact and the choices the ECU has to make.
He probably reads it at night when he can't sleep.

[boscoe99]

Makes you appreciate that little black box on the motor. It may be stupidly simple if all you consider is it takes a signal in and sends out a signal but there is an awesome amount of work it does to get that signal out for you to go scooting down the lake hunting that next big catch!

Thank you Boscoe for your info, I bookmark these for reading just to know what is going on not that I can fix anything but just to understand just a bit more.

I bet somewhere some little Jap engineer has a full library of diagrams and flow charts on how all of these interact and the choices the ECU has to make.
He probably reads it at night when he can't sleep.

It might keep him up all night thinking about all the exciting (to him) stuff that needs to be thought of. I knew an engineer who was so proud of his work and would take hours and hours to explain all of the minutia. If you asked him what colour the landing gear was painted an hour later he would be explaining stress and strain and how drop tests were performed. I admired his passion.

[99yam40]

I once asked an electrical engineer what his thoughts (yes or no answer would take care of the question) were on a problem I was having with a large rectifier unit( output of about 800VDC at 70K amps).
He took many minuets to say he could not help me because his boss told him my unit was not one of his priorities to spend his time on in a round about way

[oldmako69]

So how come they run like a string trimmer all day, and then poop the bed when you're idling up the creek home??

[pstephens46]

I once asked an electrical engineer what his thoughts (yes or no answer would take care of the question) were on a problem I was having with a large rectifier unit( output of about 800VDC at 70K amps).
He took many minuets to say he could not help me because his boss told him my unit was not one of his priorities to spend his time on in a round about way

Nobody ever said engineers were good with politics!

Know what is rare????

An engineer that can sell! There are a few. They are paid well.

[ausnoelm]

There is lots of equipment all around us that uses very sophisticated technology, but we just take it for granted, your TV set for instance, in lots of ways, its a lot more complicated than your outboard, your GPS, the computer you are looking at now, lots of things, people just use until it breaks, and except for a handful of people, no one cares how they work, even the repair person mostly doesn't need to know how individual work internally, just like the outboard tech, they use knowledge and instruments to measure known inputs and outputs.

[panasonic]

You're way over thinking it, all you need to know (unless you are getting into design or manufacture) is there is a device that determines the air temp, then in a jiffy, the ECU knows how much fuel and air is needed, if the timing needs to be advanced and so on, exactly how it does it is not adjustable by the user, nor is it important to the user or mechanic/technician.

I am firm believer in the more you know about something (outboard ECU in this case) the better you can see the "BIG PICTURE" of how it all comes together in the end. Even if you cannot change parameters or repair it.

In my case, when you get a aircraft type endorsement rating you learn plenty of "basics" about what is happening inside the aircraft system components. Most of which you are not allowed to break the seal on and repair...especially the multitude of computers on board. When they don't work...its remove and replace.

They go back to the manufacturer for repair and testing (they are the only ones who actually knows what in hell is going on inside) But I do think it helps to know what is basically going on when trying to troubleshoot a problem...others think if you cant take it apart why know what is happening inside at all.

I do know the boss don't like when you change a engine ECU, it goes out for repair and comes back with a $30,00O bench test bill with "NO FAULT FOUND"

[99yam40]

I know electricity , and electrical devices well enough to be able to work on computers to make them go again after they fail, but know nothing about the ones and zeros that make it do all the stuff it does.
I am OK with that

[dray0151]

The 1 an 0's are the fun part of the puter, it's brains that tell it what it's supposed to do. without those 1's and 0's nothing would get done.

Very first course I had in computer science was machine language, an 21 year old back in the early 70's playing with 1 and 0!!!! All done on punch cards!

[99yam40]

I can take apart most things to see what makes them tick. Have done that most of my life.

I cannot do that to see the ones and zeros, so I just never got into that.

did deal with some ladder diagrams, programming simple little control devices.

I guess they also were 1s and 0s.
contacts made up or not