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BASIC EFI Explained..........

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Just thought I would take a couple minutes and maybe inadvertently answer a few questions about EFI systems. Several years ago I began the process of learning about the system that would one day completely replace the ever beloved carb. I am not claiming any type of expertise on this subject, but I though I would make an attempt to possibly answer some of the basic questions that many riders are curious about.

Just keep in mind, as you read, that an EFI system is not entirely different than that of a traditional carburetor. Both ultimately perform the same function, just not with the same precision. Each adjustment to your base fuel program can be related to a change in jets on a carb. The main difference being a carb is a piece of hardware that uses these jets to make general changes to the air fuel mixture, and an EFI system uses software to make very minute changes to very specific areas of the air fuel mixture.

First off, EFI in my opinion is much more efficient than any carb could ever be. Please let me explain. I know that there are many good carb tuners out there that are, or have been, unwilling to accept the “new” transition to computer based systems. I know that these same individuals can tune a carb to run very smoothly. I’m not comparing a finely tuned carb to an un-tuned EFI system. Instead, I am speaking of a finely tuned carb side by side with a professionally tuned EFI system. When tuning a carb, in order to resolve a lean or rich fuel mixture in a particular “area” of the AFR (air fuel ratio), it is predominantly done so by changing the pilot jet, main jet, or even both. These jets come in various sizes (openings) to allow different volumes of gravity fed fuel to enter the carb. Changing of a jet may indeed correct the AFR in the desired area, but it also changes the AFR in that entire “range”. Meaning, if you are at 10% throttle and 4000 RPMs, and you need to increase the AFR (which leans the fuel) due to a hesitation in throttle response, then you will inadvertently change the AFR at say 15% throttle and 4000 RPMs. But what if the bike wasn’t hesitating at the 15% throttle position? Well, there is no way to separate those two conditions by use of a carb. So the correction of one issue in one area may introduce an issue in another area. Now lets look at the same situation using EFI. The fuel delivery of EFI is done by means of a pressurized system that consistently feeds fuel to the injector. By use of a Fuel Tuner/Programmer (FMF Power Programmer or Power Commander III etc) you can easily fine tune for specific areas. Granted the FMF is not as adjustable as the PCIII, but is still much more specific than the adjustments on a carb. The PCIII will allow AFRs to be adjusted in intervals of 250 RPMs and (if memory serves me correctly) Throttle Positions of 0%, 2%, 5%, 10%, 15%, 20%, 40%, 60%, 80%, and 100% (or WOT). So if you begin a spread sheet from 750 RPMs and continue in 250 RPM increments to say 11,000 RPM, and you do so for each of the Throttle Positions, you can see the amount of fine tuning that takes place. So I ask, how can a carb ever be expected to compete with such a system, given each are tuned correctly? It just can’t. There will still be those that argue the subject at hand, but it just isn’t possible.

Now lets discuss the basic types of EFI systems. There are many different types of EFI systems available, but most are based off of one of two generally organized systems. The first is what is referred to as an “open loop” system. This is a system that sends a signal to the injector based on a predetermined program, also known as a Fuel Map. This program may still include each of the TPS/RPM settings as discussed previously, however, the system does not “check” to see how a given signal/instruction affected the outcome. This signal is simply a “slave” to the program from which the instruction came from. This “check” has to be done by an experienced tuner by means of a dyno and additional analyzing equipment. Usually an EGA (Exhaust Gas Analyzer) is used in this process. This will tell the tuner what effect each signal change has on the final exhausted AFR mixture. If the EGA shows specific readings at a given RPM/TPS, for instance, then the tuner can make very specific adjustments to “just” that area of the program. That adjustment will have NO effect on any other area of the program. The down side to this system is that the tuning adjustments are made during a specific time period with a specific set of conditions, such as air temp, elevation etc. Once those conditions are changed, either by general temperature change or an elevation change during a ride, the ECU has no way of receiving input for those changes. The second basic type of EFI system is referred to as a “closed loop” system. This system is much like the first, with the exception of using onboard sensors to help determine the amount of time the signal is sent to the injector. The ECU will gather data from any available sensors and make changes to the preprogrammed fuel map based on this input. This “closed loop” system is much more effective than the “open loop” system due to its ability to receive real time information about the engine and its current condition. During a ride that includes elevation change, temperature change, and even load on the engine due to inclines etc, the ECU will make the necessary adjustments to the Map in order to maintain optimum AFRs for that motor and within its set perimeters. The level, or percentage, of change will be determined by how advanced the system is. These changes may be as small as a 3% or as much as 25% (possibly even higher) difference from the preprogrammed fuel map.

Next lets look at some of the sensors used by the ECU to help determine the pulse width of the injector. EFI systems have many sensors that feed input to the ECU (Electronic Control Unit or Computer). These sensors, depending on which type EFI system your bike has, will send data about outside air temp, engine temp, engine RPM, AFR (Determined by an O2 sensor in the exhaust), Throttle Position (TPS – Throttle Position Sensor), Manifold Pressure (MAP – Manifold Absolute Pressure), and crank shaft position. Not every system has, or utilizes, all of these sensors. That depends a lot on whether the system is Closed Loop or Open Loop. Despite the belief of many, the computer does not control the amount of fuel pressure to the injector. The injector is a piece of hardware that will only release fuel at a specific rate. There are different injectors that will increase or decrease this given rate. Kind of like the difference between a garden hose and a fire hose. Obviously one allows much more water to flow when compared to the other. What the ECU does is increases, or decreases, the signal length to the injector (also known as pulse width). This allows more or less fuel to pass through the injector based on the length of signal. This pulse width is very precise and is adjusted by the ECU in milliseconds.

Once again, I do not claim to be an expert on this subject. I’m sure someone here will make an attempt to prove that point. My objective here was to “simply” explain EFI systems and how they “generally” operate. This is very basic explanation that may help in someone’s understanding of our machines and how they work. I just thought I would share in my many hours of working on, reading about, and attempting to understand more of what our future with EFI consists of.

I hope this will be helpful to someone. If anyone would like to share any information that will add to my basic understanding, I would be more than grateful.

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I've always thought that my .net codes are massive.... :busted:

thanks for sharing :moon:

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Thanks Zadok...nice explaination,I have being trying to find out a bit out our FI systems. I can see how a nicely tuned FI is the best way to have your bike working at its best. I do have some issues with my wr250r however in the way the FI is working for me without any mods. For me I do not want to spend the 300 or so extra dollars on this tuning option and my bike is not responding good at low revs to throtle requests. I bought this bike for reliabilty and dual sport fun. It just seems funny that Yamaha can build a bike that has this lag time and tendency to die at throtle requests from low revs. Shops tell me to buy mapper etc but I keep feeling someone someday will find a solution to this problem without the big expense. With my riding style I want the low end to be responsive, and thought if anything the fuel injection would be a bonus for what I would be asking from the bike but not to be. Sorry about harping about this over the last while on this site, just hoping someone might have some ideas for me short of mapper etc. 12 tooth installed and helping but this bike still has the tendency to want to die of of idle speeds....wayne

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[...]just hoping someone might have some ideas for me short of mapper etc. 12 tooth installed and helping but this bike still has the tendency to want to die of of idle speeds....wayne

Is it better off of cold idle or warm idle?

Have you disabled your EXUP valve? Stock exhaust? Stock tires?

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just hoping someone might have some ideas for me short of mapper etc. 12 tooth installed and helping but this bike still has the tendency to want to die of of idle speeds....wayne

That is just your bikes way of telling you that she wants to go faster :thinking:

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Thanks Zadok...nice explaination,I have being trying to find out a bit out our FI systems. I can see how a nicely tuned FI is the best way to have your bike working at its best. I do have some issues with my wr250r however in the way the FI is working for me without any mods. For me I do not want to spend the 300 or so extra dollars on this tuning option and my bike is not responding good at low revs to throtle requests. I bought this bike for reliabilty and dual sport fun. It just seems funny that Yamaha can build a bike that has this lag time and tendency to die at throtle requests from low revs. Shops tell me to buy mapper etc but I keep feeling someone someday will find a solution to this problem without the big expense. With my riding style I want the low end to be responsive, and thought if anything the fuel injection would be a bonus for what I would be asking from the bike but not to be. Sorry about harping about this over the last while on this site, just hoping someone might have some ideas for me short of mapper etc. 12 tooth installed and helping but this bike still has the tendency to want to die of of idle speeds....wayne

Have you adjusted your idle setting? There is an idle adjustment on the bike, very similar to a carb. You can run the idle up which should make a pretty big difference on whether the bike dies a low rpm. I had the same issue, until I adjusted idle.

BTW....you can spend about 200 dollars on an FMF Power Programmer that will greatly help with some of the response issues

you are dealing with. It isnt nearly as detailed as the PCIII, but you also do not need a dyno tune to program. There have been

several others here who have had the FMF dyno tuned, and you can try and use their numbers if need be. The FMF system is

also much more user friendly and just overall easier to use. I have used the PCIII on several bikes to date, including working with

many others on install, programming, and adjustments on their bikes. I chose the FMF for this bike due to its simplicity.

Just something to consider.

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Is it better off of cold idle or warm idle?

Have you disabled your EXUP valve? Stock exhaust? Stock tires?

yes stock exhaust and tires, just the 12 tooth on front. Warm or cold same problem. Dont know what a exup valve is so I will read up on it from my manual. Thanks for the tips folks I will turn up my idle speed in the mean time I am sure this will help a bit

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Thanks Zadok. Too early to tell for sure here as too much snow on the ground. But testing in the garage just in neutual and giving it some revs tells me things are better now with idle up. Big difference. Any danger turning the adjuster screw out to far, not sure if it has a stop built in or if it can fall out? Thanks again I will update this post when the ground drys up next week...wayne

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Warm or cold same problem.

Dont know what a exup valve is so I will read up on it from my manual.

If you haven't messed with your exhaust, then your EXUP is still working.:thinking:

Since it is the same warm or cold, I agree with Zadok's suggestion of bumping up the idle rpm as the easiest thing to do. You may find it helps "just enough."

I *think* the recommended warm idle rpm range is 1450-1650.

I don't know what harm, other than increased fuel usage and making a little more heat at idle, could come from setting it higher than 1650.

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If you haven't messed with your exhaust, then your EXUP is still working.:thinking:

Since it is the same warm or cold, I agree with Zadok's suggestion of bumping up the idle rpm as the easiest thing to do. You may find it helps "just enough."

I *think* the recommended warm idle rpm range is 1450-1650.

I don't know what harm, other than increased fuel usage and making a little more heat at idle, could come from setting it higher than 1650.

I dont know that there is any harm in doing so either. I know from

experience with my bike, the idle from bike to bike is not the same.

Dont know why.

Anyway, hope it helps.

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Thanks Zadok...nice explaination,I have being trying to find out a bit out our FI systems. I can see how a nicely tuned FI is the best way to have your bike working at its best. I do have some issues with my wr250r however in the way the FI is working for me without any mods. For me I do not want to spend the 300 or so extra dollars on this tuning option and my bike is not responding good at low revs to throtle requests. I bought this bike for reliabilty and dual sport fun. It just seems funny that Yamaha can build a bike that has this lag time and tendency to die at throtle requests from low revs. Shops tell me to buy mapper etc but I keep feeling someone someday will find a solution to this problem without the big expense. With my riding style I want the low end to be responsive, and thought if anything the fuel injection would be a bonus for what I would be asking from the bike but not to be. Sorry about harping about this over the last while on this site, just hoping someone might have some ideas for me short of mapper etc. 12 tooth installed and helping but this bike still has the tendency to want to die of of idle speeds....wayne

The bike runs very lean stock, especially at idle, this is a way to help pass emissions regulations. Unfortunately, the PCIII or FMF tuner are really the only true "solutions" to your issue. I too was very disappointed the first time I rode the bike and had such horrendous stumbling issues, and yes it was nice to just be able to run down to the shop and buy ten bucks worth of pilot and main jets, but unfortunately the advantages of FI are such that the expense of a power commander is well well worth it for those who have the intention of modifying the bike. For those of us who just wanted a nice running run-about in stock form..... I think Yamaha missed the mark. Heck it is a brand new model, maybe they will update the fuel maps and have new ecu's available at a more reasonable price in the next couple years.

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