Open and closed
Posted: Thu Sep 21, 2006 9:41 am
A couple of days ago I was hanging out in the show room of the Pro Caliber motorcycle dealership talking to Shaun (tuff puff). Since many of the new quads are coming out with fuel injection, we got on the topic of what open and closed loop meant when referring to types of fuel injection. A hand full of the guys in here are switching over to fuel injected engines, so I thought a short explanation of what it means when some one says open loop or closed loop might help.
There is a WHOLE lot a person could write just on what this means. I wont go into big detail because that gets boring. This is to just give you a general grasp of the terms.
Okay...I will start with "closed loop" this is what most of the cars on the road are running today. They do switch from closed to open in certain circumstances...but I wont get into that. Basically, what closed loop means...is the car's/motorcycle's/whatever's computer is receiving "feedback" from the sensors on the engine. In example...the O2 sensor in the exhaust is sensing how rich or lean your fuel/air mixture is. If it senses that it is too rich, then it tells the computer that it is too rich, the computer then listens to the feedback from the O2 sensor and will make the fuel injectors squirt less fuel. Obviously...a lean reading would cause the computer to do the opposite. This system is taking readings from the engine's sensors hundreds, and on some, thousands of times per second. The machinery it takes to do this is somewhat complicated...but as you can see...the action itself is pretty simple (no voodoo).
Now...an open loop system, which many (most) of the after-market systems and motorcycles are... is really very similar to the closed loop. Here is the difference....The open loop is still listening to sensors...the difference is, it does not adjust according to what an O2 sensor says the fuel is. An open loop system has a fuel map set in place...and no matter how rich or lean the fuel may be...it is going to stick with the fuel map that has been programmed into it. It knows to give X amount of fuel at a given throttle position and that is what you are going to get. Like..."I was told to do this and I don't care what else may be happening...I am going to do what I was told".
You may be wondering why anyone would even run an open loop system. I mean...a closed loop makes sure that your fuel mixture is always good. This is one of those "yes and no" answers. I don't want to get too deep into this, so lets just say that a motor at certain rpms does not always perform the best at what the O2 sensor sets. Ever notice that a factory fuel injected car has a slight "lag" or wind up when you blip throttle really quick? Most of you wont notice this while driving and if you have never had a hot car with a carb...you might not even notice the difference...believe me when I tell you that the engine response from a stock fuel injected car is slow. The reason for this is that even though the computer is getting readings many times a second...it still has that split second where it needs to figure out what you just did and then relay that to the injectors/ timing. Now on an open loop...it does not have to figure out what you are doing...it knows that when the throttle is at 40% open, it gives you X amount of fuel, so it is almost instant. Kind of like a boxer...no matter how brilliant a guy is and how much he thinks about the next punch he is going to throw and how perfect that punch is going to be... the guy that has it programmed into him like a reflex, that requires no thought, is going to smash your nose all over your face while your still doing the math. This is one of the reasons why they put open loop on motorcycles and quads...so there is no delay when you need power RIGHT NOW. Also...and open loop can be programmed to the way you want it...kind of like jetting a carburetor, but WAY more accurate. If you think (or know) you need a little more fuel at 4,530 rpm...then you can program that into your fuel map. This kind of "re-mapping" is best left to guys with an Eddie current dyno, an EGA (exhaust gas analyzer) and experience. You can buy pre-set programs from guys who have all of this equipment and have already done all the experimenting to find out where your car/motorcycle makes the most power. It's hundreds of hours of labor, dyno time and tuning on different engine combinations. When they feel they have hit it right on the money, they sell it for you to download it into your computer. Whether they know what they are doing or not is really your job to find out before you buy what they sell. I have personally dealt with some maps from companies that just darn near make the motorcycle lose power. I personally can fix their screw ups and re-map it...most don't really know where to start...so be careful about who you buy from...do your research.
Anyway...that is the very basics of what open and closed means when talking about fuel injection...In case you wanted to know.
There is a WHOLE lot a person could write just on what this means. I wont go into big detail because that gets boring. This is to just give you a general grasp of the terms.
Okay...I will start with "closed loop" this is what most of the cars on the road are running today. They do switch from closed to open in certain circumstances...but I wont get into that. Basically, what closed loop means...is the car's/motorcycle's/whatever's computer is receiving "feedback" from the sensors on the engine. In example...the O2 sensor in the exhaust is sensing how rich or lean your fuel/air mixture is. If it senses that it is too rich, then it tells the computer that it is too rich, the computer then listens to the feedback from the O2 sensor and will make the fuel injectors squirt less fuel. Obviously...a lean reading would cause the computer to do the opposite. This system is taking readings from the engine's sensors hundreds, and on some, thousands of times per second. The machinery it takes to do this is somewhat complicated...but as you can see...the action itself is pretty simple (no voodoo).
Now...an open loop system, which many (most) of the after-market systems and motorcycles are... is really very similar to the closed loop. Here is the difference....The open loop is still listening to sensors...the difference is, it does not adjust according to what an O2 sensor says the fuel is. An open loop system has a fuel map set in place...and no matter how rich or lean the fuel may be...it is going to stick with the fuel map that has been programmed into it. It knows to give X amount of fuel at a given throttle position and that is what you are going to get. Like..."I was told to do this and I don't care what else may be happening...I am going to do what I was told".
You may be wondering why anyone would even run an open loop system. I mean...a closed loop makes sure that your fuel mixture is always good. This is one of those "yes and no" answers. I don't want to get too deep into this, so lets just say that a motor at certain rpms does not always perform the best at what the O2 sensor sets. Ever notice that a factory fuel injected car has a slight "lag" or wind up when you blip throttle really quick? Most of you wont notice this while driving and if you have never had a hot car with a carb...you might not even notice the difference...believe me when I tell you that the engine response from a stock fuel injected car is slow. The reason for this is that even though the computer is getting readings many times a second...it still has that split second where it needs to figure out what you just did and then relay that to the injectors/ timing. Now on an open loop...it does not have to figure out what you are doing...it knows that when the throttle is at 40% open, it gives you X amount of fuel, so it is almost instant. Kind of like a boxer...no matter how brilliant a guy is and how much he thinks about the next punch he is going to throw and how perfect that punch is going to be... the guy that has it programmed into him like a reflex, that requires no thought, is going to smash your nose all over your face while your still doing the math. This is one of the reasons why they put open loop on motorcycles and quads...so there is no delay when you need power RIGHT NOW. Also...and open loop can be programmed to the way you want it...kind of like jetting a carburetor, but WAY more accurate. If you think (or know) you need a little more fuel at 4,530 rpm...then you can program that into your fuel map. This kind of "re-mapping" is best left to guys with an Eddie current dyno, an EGA (exhaust gas analyzer) and experience. You can buy pre-set programs from guys who have all of this equipment and have already done all the experimenting to find out where your car/motorcycle makes the most power. It's hundreds of hours of labor, dyno time and tuning on different engine combinations. When they feel they have hit it right on the money, they sell it for you to download it into your computer. Whether they know what they are doing or not is really your job to find out before you buy what they sell. I have personally dealt with some maps from companies that just darn near make the motorcycle lose power. I personally can fix their screw ups and re-map it...most don't really know where to start...so be careful about who you buy from...do your research.
Anyway...that is the very basics of what open and closed means when talking about fuel injection...In case you wanted to know.
