Open and closed

scott the viking · Post by **scott the viking** » 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.

bajaherbie · Post by **bajaherbie** » Thu Sep 21, 2006 9:51 am

good post. but now i'm really confused

which bike did you buy?

scott the viking · Post by **scott the viking** » Thu Sep 21, 2006 9:58 am

bajaherbie wrote:good post. but now i'm really confused

which bike did you buy?

Which part do you want me to go into farther?

And Noway I would buy a bike from that slickster pimp.

Big Dave · Post by **Big Dave** » Thu Sep 21, 2006 10:57 am

So while were on the subject, is this an open loop system?
http://www.cbperformance.com/catalog.asp?ProductID=287
The kit comes with an O2 sensor, so why would an open loop system need one?
It seems to me that good economy mandates a closed loop system so it can compensate for altitude changes, which is important to me.

tuff_puff · Post by **tuff_puff** » Thu Sep 21, 2006 11:53 am

scott the viking wrote:
And Noway I would buy a bike from that slickster pimp.

Hey i resemble that remark!

scott the viking · Post by **scott the viking** » Thu Sep 21, 2006 12:11 pm

Big Dave wrote:So while were on the subject, is this an open loop system?
http://www.cbperformance.com/catalog.asp?ProductID=287
The kit comes with an O2 sensor, so why would an open loop system need one?
It seems to me that good economy mandates a closed loop system so it can compensate for altitude changes, which is important to me.

A lot of kits are being built with both. So, open loop where you need it most and closed loop where you need IT the most. Like a best of both worlds kind of thing. Most of them that are set this way will run closed loop while idling or cruising...as in, not pulling hard or accelerating fast. The kind of performance most need/want in those areas are just smooth operation..not the most power. It will switch to open loop normally from a throttle position sensor. Push it so far down and it goes to the pre-set map. Some are higher tech and change after taking a few other things into account.

Skidmark · Post by **Skidmark** » Thu Sep 21, 2006 7:10 pm

Scott,
Do you have any experience with the EMS Stinger set up? One of the first places I plan on driving my car to is back to the engine shop for a dyno session. I have no idea if this set up is open or closed loop (or both) but I have heard good things from others using it. Just not real technical info...

Post by **Leatherneck** » Thu Sep 21, 2006 7:23 pm

Damn hate when this happens but little off subject, Skid how does the EMS react to the elements?

Back to your regular program.

Skidmark · Post by **Skidmark** » Thu Sep 21, 2006 7:32 pm

What elements? There aren't any elements in my garage...

You actually forgot my car isn't done yet? I have only been working on it for a year. I think the latest projection for completion involved another U.S. President in office if I remember...

It will be enclosed in a sheet metal box before it is driven. That will protect it from any elements. The car is a permanent convertible as well, so no rain driving. An enclosure will be enough for the occasional river/stream/puddle crossings, dirt, rocks, and such.

takotruckin · Post by **takotruckin** » Thu Sep 21, 2006 7:53 pm

Skidmark wrote:What elements? There aren't any elements in my garage...
You actually forgot my car isn't done yet? I have only been working on it for a year.

hahahaha

scott the viking · Post by **scott the viking** » Thu Sep 21, 2006 8:28 pm

Skidmark wrote:Scott,
Do you have any experience with the EMS Stinger set up? One of the first places I plan on driving my car to is back to the engine shop for a dyno session. I have no idea if this set up is open or closed loop (or both) but I have heard good things from others using it. Just not real technical info...

I have not messed with the Stinger...but I think it is very similar to some I have. I am pretty sure the stinger is an open loop. Did it come ready for an O2 sensor?
If it runs really strong with no burps through out most of the rpm range...a dyno tune will pretty much focus on dialing in the upper rpm power.. Unless you are taking it to an Eddie current style dyno and the guy uses an EGA. Eddie current mean he can simulate road resistance at cruise speed by putting a load on the dyno's drum. Doing this with an EGA hooked up is like tuning and driving at the same time. He can get pretty much every parameter just right.

Post by **Leatherneck** » Thu Sep 21, 2006 8:37 pm

Hey Scott first off let me say this is some outstanding info. When I do get my subie hooked up I am tossing the stock ECU and harness but a problem here is what if you do not have a Dyno handy? Is there another way for a person to get close or would it be hit and miss? I have seen some guys fine tuning (or say they are) there engines with just a lap top hooked in to the EMS. Are they just setting it back to other saved settings?

Skidmark · Post by **Skidmark** » Thu Sep 21, 2006 8:45 pm

Did it come ready for an O2 sensor?

I bought the engine turn key - it was all hooked up when I got it. This may sound stupid, but I haven't even looked at that close. Brought it home, bolted it in, turned the car around and started on the front end again...

scott the viking · Post by **scott the viking** » Fri Sep 22, 2006 6:42 am

Leatherneck wrote:Hey Scott first off let me say this is some outstanding info. When I do get my subie hooked up I am tossing the stock ECU and harness but a problem here is what if you do not have a Dyno handy? Is there another way for a person to get close or would it be hit and miss? I have seen some guys fine tuning (or say they are) there engines with just a lap top hooked in to the EMS. Are they just setting it back to other saved settings?

Yeah...guys that are running on the street and "fine tuning" are either switching back between saved maps...or they belong on "the short bus" for thinking they can mess with the internals of a map on the fly. You don't "need" a dyno...the car will run SOOO much better than you ever dreamed that you probably will think that it is not needed. True...you can inch that extra hp out with a good dyno tuner...but chances are...the Suby will take a year or two just to get used to the power...yeah...it is that good...What is REALLY shocking with these motors is the amount of low end power...like right off a slow cruise where most engines need rpm built to take off...the Suby will just launch.

scott the viking · Post by **scott the viking** » Fri Sep 22, 2006 6:46 am

Skidmark wrote:
Did it come ready for an O2 sensor?
I bought the engine turn key - it was all hooked up when I got it. This may sound stupid, but I haven't even looked at that close. Brought it home, bolted it in, turned the car around and started on the front end again...

Then chances are...most of the "bugs" have been worked out for you. I am sure that a little fine tuning can probably help when you get around to it though. I mean...it's not like you bought a carb and now you have to tune it to your engine...the guys that put the ECM together new what it was going on and did most of the tuning work for you. Probably just a couple of edges to smooth out.