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Discussion Starter #1 (Edited)
Having been on this forum for about 2 years now, I’ve asked, read and answered a lot of questions. As Polaris keeps making more machines with EFI, it stands to reason that more and more of the the problems & questions are related to the EFI system, its sensors and electronics. That being said, I thought I would try to explain in general how an EFI system works on an ATV. Hopefully this helps take the mystery out of how EFI operates. In the right hands, an EFI system can be checked and diagnosed with a fuel pressure gauge, a multimeter, a factory manual, and access to forums such as this one for the special tool workarounds. In fact, most of this information is right out of the factory manuals for a 2006 700 Twin Cylinder EFI and a 2007 500 EFI.

First and only quote from the manual: "80% of all EFI problems are caused by wiring harness connections."

ELECTRONIC FUEL INJECTION 101:

OVERVIEW:

The central component of the system is the ECU which manages system operation, determining the best combination of fuel mixture and ignition timing for the current operating conditions. An in-tank electric fuel pump is used to move fuel from the tank through the fuel line and in-line fuel filter. The in-tank fuel pressure regulator maintains a constant system operating pressure and returns any excess fuel to the tank. At the engine, fuel is fed through the fuel rail and into the injectors, which protrude into the intake ports. The ECU controls the amount of fuel fed to the engine by varying the length of time that the injectors are energized. The controlled injection of the fuel occurs on each crankshaft revolution, or twice for each 4-stroke cycle. One-half the total amount of fuel needed for one firing of a cylinder is injected during each revolution. When the intake valve opens, the fuel/air mixture is drawn into the combustion chamber, ignited, and burned.

The ECU controls the amount of fuel being injected and the ignition timing by monitoring the primary sensor signals for air temperature, barometric air pressure, engine temperature, engine speed (RPM), and throttle position (load). These primary signals are compared to the programming in the ECU computer chip, and the ECU adjusts the fuel delivery and ignition timing to match the values.

The ECU has the ability to compensate on-the-fly for changes in overall engine condition and operating environment. This allows it to maintain the ideal air/fuel ratio regardless of temperature, demand, or altitude.

During certain operating periods such as cold starts, warm up, acceleration, etc., a richer air/fuel ratio is automatically calculated by the ECU.

FUEL:

Fuel Pump – Located inside the tank, this electronic pump draws fuel through a 30-micron filter sock on the bottom of the tank and maintains a constant flow of about 25 liters per hour. That’s about 7-8 gallons per hour which far exceeds demand. The fuel pump operates on as low as 7 volts.

Fuel Pressure Regulator – Located just above the pump on the inside of the tank. It maintains a constant pressure of 39 +/- 3 psi by diverting the excess fuel from the pump back into the tank. This is considered a “closed” system as opposed to an “open” system that has the regulator on the fuel rail and a return hose to the fuel tank. Unlike a car, there is no vacuum reference port so the fuel pressure doesn’t rise and lower with demand.

Fuel Lines – Hard-sided hoses with quick-disconnects on each end. There are two: one from the tank to the inline filter, and one from the filter to the fuel rail.

Fuel Filter – Located behind the frame member that is just aft of the radiator cap. A cylinder about 4 inches long and 2 inches in diameter with quick-disconnect receptacles on each end. Fuel passes through the 10-micron element inside.

Fuel Rail – A metal tube fitted on top of the fuel injector(s) and attached to the cylinder head. Fuel passes through the fuel rail on the way to the injector(s) and the rail holds the injectors in place. It has a Schrader valve (bicycle valve) at the end where you can attach a fuel pressure gauge or push the valve in and relieve the pressure from the system.

Fuel Injector(s) – Located on the cylinder head. These are spark-plug sized mechanisms with a wiring harness attached. They open when energized for 1.5-8.0 milliseconds (called a “pulse width”) to let fuel pass through the spray nozzle. If removed, you will see a rubber O-ring on each end and a small filter screen on the intake end.

IGNITION:

Battery/Charging System – Efficient operation of the EFI system depends on a fully charged battery and properly operating charging system. The Ignition Coils paragraph will explain why.

Ignition Coils – Located under the left front fender mounted on the frame. On an EFI machine the DC/CDI system relies on battery power for ignition. Instead of generating DC voltage via magnetic induction (a.k.a. the stator), a 12 volt DC current is supplied directly to the ECU from the battery. 12 volt DC current charges an internal capacitor to build up the initial ignition charge. An A/C signal from the Crank Shaft Position Sensor is processed by the ECU, which determines ignition timing by calculating from a point pre-determined in the crankshaft rotation. This signal releases the electrical charge which saturates the coil for ignition. DC/CDI systems have the ability to ignite with as little as 6 volts of power.

EFI SYSTEM:

Engine Control Unit (ECU) – Located against the frame directly below the headlight pod. The ECU is the brain of the entire EFI system and requires a minimum of 7.0 volts to operate. The memory in the ECU is operational the moment the battery cables are connected. Sensors continuously send data to the ECU. Signals to the ECU include: ignition (on/off), crankshaft position/speed (RPM), throttle position, engine coolant temperature, air temperature, and intake manifold air pressure and battery voltage. The ECU compares the input signals to the programmed maps in its memory and determines the appropriate fuel and spark timing requirements for the immediate engine cycle. The ECU then sends output signals to set the injector duration and ignition timing for that engine revolution. That equates to one output signal from the ECU for every RPM, which can be over 6,000 times per minute, or 100 times per second!

Throttle Body / Intake Manifold – The throttle body is located in the forward end of the throttle body intake boot. It houses the throttle cable attachment cam, the throttle plate (butterfly), and the TPS. On single cylinder engines, it also houses the IAC. The intake manifold is located between the cylinder head and the output side of the throttle body.

Check Engine Light (MIL or Malfunction Indicator Light) – During operation, the ECU continually performs a diagnostic check of itself, each of the sensors, and system performance. If a fault is detected, the ECU turns on the Check Engine Light (Malfunction Indicator Light) on the speedometer and stores the fault code in its fault memory. Depending on the significance or severity of the fault, normal operation may continue, or “Fail-Safe” operation (slowed speed, richer running) may be initiated. Some call this "limp mode." You can access the stored fault code using a “blink code” diagnosis flashed out through the instrument cluster.

Wire Harness Assembly – If I need to tell you what this is, perhaps I can refer you to a dealer. :)

Sensors:

With the exception of the CPS, the sensors are variable resistors that allow a certain voltage to pass through them and back to the ECU. They start with a reference voltage that comes from the ECU. As pressure or temperature increase and decrease, the amount of sensor resistance varies along with it. The ECU’s data is derived from the difference between the reference voltage and the voltage allowed to pass through the sensor back to the ECU. The ECU then translates that data into a value on its fuel map, combines it with inputs from the other sensors, and determines how much fuel to inject and when to release the coil charge to ignite the fuel.

Coolant Temperature Sensor – Mounted on the cylinder, the engine temperature sensor measures coolant temperature. The engine temperature sensor is a Negative Temperature Coefficient (NTC) type sensor, as the temperature increases the resistance decreases. Coolant passes through the cylinder and by the sensor probe, creating a resistance reading which is relayed to the ECU. This signal is processed by the ECU and compared to its programming for determining the fuel and ignition requirements. The data from this sensor, when combined with the air pressure and temperature sensor data, gives an EFI the ability to richen the fuel automatically during a cold start, just as a manual choke would. The ECU also uses this signal to determine when to activate the fan during operation. If for any reason the engine temperature sensor circuit is interrupted, the fan will default to ’ON’. Some models have an Engine Temperature Sensor for EFI inputs, and a separate Coolant Temperature Sensor mounted on the lower part of the radiator for fan operation.

Throttle Position Sensor (TPS) – Located on the throttle body and operated directly off the end of the throttle shaft. The TPS works like a rheostat, varying the voltage signal to the ECU in direct correlation to the angle of the throttle plate (engine load). This signal is processed by the ECU and compared to the internal pre-programmed maps to determine the required fuel and ignition settings for the amount of engine load. The initial position of the TPS is established and set at the factory. If the TPS is repositioned, replaced or loosened it must be initialized.

Crankshaft Position Sensor (CPS) – Located on the aft side of the stator cover. Also known as the engine speed sensor, the CPS is essential to engine operation, constantly monitoring the rotational speed (RPM) of the crankshaft. A magnetic, 60-tooth ring gear with two consecutive teeth missing is mounted on the flywheel with the inductive speed sensor (Hall Effect sensor) mounted immediately next to it. During rotation, an AC pulse is created within the sensor for each passing tooth. The ECU calculates engine speed from the time interval between the consecutive pulses. The two-tooth gap creates an “interrupt” input signal, corresponding to specific crankshaft position for PTO cylinder. This signal serves as a reference for the control of ignition timing by the ECU. On twin cylinder engines, synchronization of the CPS and crankshaft position takes place during the first two revolutions each time the engine is started. On single cylinder engines, synchronization also includes the Manifold Air Pressure Sensor. The CPS must be properly connected at all times. If it fails or becomes disconnected for any reason, the engine will quit running.

Intake Air Temperature (IAT) – Found on single cylinder engines, the IAT is located on the rear of the air box. It protrudes into the box to measure charge air temperature for the ECU.

Manifold Air Pressure Sensor (MAP) – Found on single cylinder engines, it is located on the throttle body intake boot. It measures air pressure for fuel/air mixture calculations. It also identifies to the ECU which stroke is the intake stroke, which was determined during synchronization.

Intake Air Temperature – Barometric Air Pressure Sensor (T-BAP) – On the twin cylinder engines, the IAT & MAP sensors are combined into one sensor called the T-BAP, which is located on the throttle body intake boot.

Note: Based on air temperature and pressure, the ECU can calculate the density of the air and adjust the fuel output accordingly. This is what gives the EFI system the ability to automatically adjust for altitude changes—a distinct advantage over carburetors.

Idle Air Control Motor (IAC) – Used on single cylinder engines and located on the throttle body. The IAC is used to stabilize the idle quality of the engine. The IAC is a stepper motor that receives varying voltage inputs from the ECU. The amount of voltage determines the IAC plunger setting, which in turn controls the amount of air bypassing the closed throttle body for idle control. If the IAC is disconnected or inoperative, it will remain at its last setting.
 

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Thank you so much for taking the mystery out of the magic of EFI. It now makes sense to me what the ECU is doing to rplace my good old carburator. I feel more prepared to tackle problems that may arise in the future with my 2 EFI machines.
 

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QUESTION I have been following your thread on fuel pump issues having similar problems, IS IT POSSIBLE that heat building up inside engine compartment create false signals to the ECU from one of these sensors--causing rough running and shutting down. I foil taped the bottom of tank and it helped some (hasn't shut down lately) but still runs rough at slower speeds, zips right along at higher speeds. Pod doesn't show ck engine lite or hot and no default codes, fuel pressure @ 42# constant on 1 1/2 hour run and at idle. GREAT JOB PRESENTING THE ABOVE INFO...... AGAIN!!!!!!!
 

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Discussion Starter #5
QUESTION I have been following your thread on fuel pump issues having similar problems, IS IT POSSIBLE that heat building up inside engine compartment create false signals to the ECU from one of these sensors--causing rough running and shutting down. I foil taped the bottom of tank and it helped some (hasn't shut down lately) but still runs rough at slower speeds, zips right along at higher speeds. Pod doesn't show ck engine lite or hot and no default codes, fuel pressure @ 42# constant on 1 1/2 hour run and at idle. GREAT JOB PRESENTING THE ABOVE INFO...... AGAIN!!!!!!!
Thanks for the kind words.

While it's possible, in general I don't think so. Except for the fuel pump, the components that aren't heat related are pretty sheltered from any heat-producing engine components. The ones that are near heat are supposedly engineered to withstand it.

Based on your problem description, it looks more and more like your solution may be a new fuel pump; but I know you were kind of waiting for a definitive result from my other thread. I would look again at the TPS, IAT, MAP or T-BAP wiring harnesses (remember the 80% solution).

I don't know if you saw the update on the other thread but I did ride last weekend and the 700 ran great with the new Carter fuel pump. Burned about 7/8 of a tank and worked it real hard--no problems at all. I personally believe it's OK but I'm a little gun-shy about calling it good nowadays. Believing and knowing are 2 different things. I want to ride several times to make sure. I have a 4-day ride planned over Memorial Day weekend and that should be conclusive.

BTW, I'm pretty sure you've told me what kind of machine you ride and sorry I can't remember. If you would describe your machine in your signature it would always be there and would help focus the answers from anyone you ask questions of.

Stew
 

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Its a 2005 700 EFI. I hooked up a pressure tester and took a ride for about an hour and half and it pegged at 42# and never waived until I ran out of gas (deliberate) Put gas in and it pegged at 42 again, even at idle it stayed at 42however it still ran with a light stutter. I am skeptical about pressure now, but????????. I wonder if the heat warming up the air box for instance and having the TBap sending wrong air temp or BP to the ECU or gas at a higher temp or something like this would make a differance. As far as being eng for this, I have worked with eng and arch all my life, big co's don't really care if it fails or has problems ( designed obsolescence)
 

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Bells are ringing,,,, re re read your thread, I noticed yesterday while riding, the fan would come on and not shut off all the while I was riding.. Would this have something to do with my problems,, I just bought this quad and am not familiar with it yet, I hope he didn't bypass hot to sell bike
 

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Discussion Starter #8
Its a 2005 700 EFI. I hooked up a pressure tester and took a ride for about an hour and half and it pegged at 42# and never waived until I ran out of gas (deliberate) Put gas in and it pegged at 42 again, even at idle it stayed at 42however it still ran with a light stutter. I am skeptical about pressure now, but????????. I wonder if the heat warming up the air box for instance and having the TBap sending wrong air temp or BP to the ECU or gas at a higher temp or something like this would make a differance. As far as being eng for this, I have worked with eng and arch all my life, big co's don't really care if it fails or has problems ( designed obsolescence)
Do you have a factory manual? The resistance specs for most of the sensors are in there. You can check them with a multimeter. Here's a writeup on checking the TPS without the special tool.

http://www.polarisatvforums.com/forums/polaris-atv-how-tos/28011-guide-tps-adjustment-testing-2010-earlier-efi-models.html

So fuel pressure is good and there is still a light stutter. Sounds like the fuel pump is working as advertised. If heat were affecting the sensors I don't think the problem would be very intermittent but would be fairly constant. Without hearing it, it's hard to tell. That's just a limitation of writing in a forum.

The manual says if the CPS is bad the engine won't run. What if the CPS is going bad or the wiring? An intermittent missed signal from the CPS would cause a light stutter because the ECU wouldn't know exactly when to fire the coil. The wiring on the sensor harnesses can appear to be good to the eye while the strands inside are actually breaking. Pull the individual wires and see if one is stretchier than the others. If so, that might be your culprit.

From the manual: The CPS is what they are calling the speed sensor. Also, use pins 9 & 10 on the ECU plug.

"CRANKSHAFT POSITION SENSOR TEST

The crankshaft position sensor is a sealed,
non--serviceable assembly. If fault code diagnosis
indicates a problem within this area, test and correct
as follows:

1. Disconnect main harness connector from ECU.
2. Connect an ohmmeter between the pin terminals.
A resistance value of 560 Ω ± 10% at room
temperature (20_ C, 68_F) should be obtained. If
resistance is correct, check the mounting, air gap,
toothed ring gear (damage, runout, etc.), and
flywheel key.
3. Disconnect speed sensor connector from wiring
harness. (the connector with one heavy black
lead) Viewing the connector with dual aligning
rails on top, test resistance between the
terminals. A reading of 560 Ω ± 10% should again
be obtained.
NOTE: If the resistance is incorrect, remove the
screw securing the sensor to the mounting bracket
and replace the sensor. If the resistance in step 2 was
incorrect, but the resistance of the sensor alone was
correct, test the main harness circuit between the
sensor connector terminals and the corresponding pin
terminals in the main connector. Correct any
observed problem, reconnect the sensor, and perform
step 2 again."
 

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Discussion Starter #9
Bells are ringing,,,, re re read your thread, I noticed yesterday while riding, the fan would come on and not shut off all the while I was riding.. Would this have something to do with my problems,, I just bought this quad and am not familiar with it yet, I hope he didn't bypass hot to sell bike
Make sure the radiator is clear of all packed dirt in between the fins just to eliminate that possibility. Also, the previous owner may have installed a switch somewhere to turn the fan on constantly, bypassing the automatic function. Look for that as well.

If there's no modifications and your coolant temp sensor circuit is inop, it will make the fan come on and stay on. It also means the ECU doesn't know the temperature of the engine. If the ECU thinks the engine is cold, it would cause a rich fuel condition, even when the engine is warm. That would be like running a carbureted machine with the choke pulled a little. Maybe you are onto something.

Coolant Temp Sensor Specs

Hot Light On
178Ω -- 190Ω @ 215° F (102° C)

Fan Off
296Ω -- 316Ω @ 180° F (82° C)

Fan On
236Ω -- 251Ω @ 195° F (91° C)
 

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Discussion Starter #10
Also check the coolant level...
 

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Coolant level was full, rad has been flushed out several times so I don't think that is it...However new plugs I had installed month ago looked perfect yesterday, if it was running rich they should have been dirtier...BUT.. it looks like I'll have to tear off covers again and go to work on checking coolant sensors, themostat and wiring. Just like to old days of snowmobles,, ride 2, work 5 days. THANKS FOR YOUR HELP STEW !!!!!!!
 

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Discussion Starter #12
:) ...but the ride 2 are worth the 5 days of work!

Stew
 

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Efi 101

Today 12:50 PM - permalinkDom1007
I would like to thank everyones info on this forum , a while back i had a problem with 2007 sportsman 500 efi not running correctly with help from many posts, one helped the most (EFI 101) I found a broken wire going to the map sensor. Now fixed wheeler is running great Thanks again Dom
 

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I have an o9 sporty 500 it runs great when it cold. But when it's hot it seems like its running rich and will stall at idle. Can a faulty AIT affect this? Or would the problem be more related to the map sensor? Just kinda want to narrow it down abit if I can. The strange thing is I don't get any codes!
 

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Hello All,
Great info here!
I recently bought a 2005 Sportsman 700 Twin, I feel like I got a good deal ($3600) but after taking it out a couple times, I am experiencing some of the symptoms described throughout this thread.
The atv starts and runs great, smooth idle at 1100 rpm +/- 20 rpm. Everything seems to work well for a while, then it will start to sputter out, and no power, just like it was running out of gas. If left to cool down for a few minutes it is fine for a while then it starts all over. One observation that seems to be different than the other posts I have read, is mine will do this with 3/4 or more gas in the tank.
Today I checked the fuel pressure and with the ignition on, but not running the pressure goes right to 40-41psi, while running it goes up to a constant 44psi.

Pressure regulator?? That does not explain why it is sputtering and running out of gas.

Any input is welcome.

 

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Its a 2005 700 EFI. I hooked up a pressure tester and took a ride for about an hour and half and it pegged at 42# and never waived until I ran out of gas (deliberate) Put gas in and it pegged at 42 again, even at idle it stayed at 42however it still ran with a light stutter. I am skeptical about pressure now, but????????. I wonder if the heat warming up the air box for instance and having the TBap sending wrong air temp or BP to the ECU or gas at a higher temp or something like this would make a differance. As far as being eng for this, I have worked with eng and arch all my life, big co's don't really care if it fails or has problems ( designed obsolescence)
Do you have a factory manual? The resistance specs for most of the sensors are in there. You can check them with a multimeter. Here's a writeup on checking the TPS without the special tool.

http://www.polarisatvforums.com/forums/polaris-atv-how-tos/28011-guide-tps-adjustment-testing-2010-earlier-efi-models.html

So fuel pressure is good and there is still a light stutter. Sounds like the fuel pump is working as advertised. If heat were affecting the sensors I don't think the problem would be very intermittent but would be fairly constant. Without hearing it, it's hard to tell. That's just a limitation of writing in a forum.

The manual says if the CPS is bad the engine won't run. What if the CPS is going bad or the wiring? An intermittent missed signal from the CPS would cause a light stutter because the ECU wouldn't know exactly when to fire the coil. The wiring on the sensor harnesses can appear to be good to the eye while the strands inside are actually breaking. Pull the individual wires and see if one is stretchier than the others. If so, that might be your culprit.

From the manual: The CPS is what they are calling the speed sensor. Also, use pins 9 & 10 on the ECU plug.

"CRANKSHAFT POSITION SENSOR TEST

The crankshaft position sensor is a sealed,
non--serviceable assembly. If fault code diagnosis
indicates a problem within this area, test and correct
as follows:

1. Disconnect main harness connector from ECU.
2. Connect an ohmmeter between the pin terminals.
A resistance value of 560 Ω ± 10% at room
temperature (20_ C, 68_F) should be obtained. If
resistance is correct, check the mounting, air gap,
toothed ring gear (damage, runout, etc.), and
flywheel key.
3. Disconnect speed sensor connector from wiring
harness. (the connector with one heavy black
lead) Viewing the connector with dual aligning
rails on top, test resistance between the
terminals. A reading of 560 Ω ± 10% should again
be obtained.
NOTE: If the resistance is incorrect, remove the
screw securing the sensor to the mounting bracket
and replace the sensor. If the resistance in step 2 was
incorrect, but the resistance of the sensor alone was
correct, test the main harness circuit between the
sensor connector terminals and the corresponding pin
terminals in the main connector. Correct any
observed problem, reconnect the sensor, and perform
step 2 again."
Like you were saying the CPS can be going bad and cause a momentary loss of spark causing a stumble, or it can go out shutting down the motor and then start back up later, I've had both on cars. As to the fuel Pressure, it shouldn't vary like oil pressure, the pump and the pressure regulator should keep this pretty constant. If you get fluctuating pressure you have an issue, possibly a pump or regulator. If it were me I'd check the CPS like AKStew stated above. If that's good possibly loose wire to the coil but fuel system sounds like it's ok.
 

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i have a polarirs 6 wheeler big boss 800 twin that only has about 500 miles on it, i usually get about 22 to 25 miles per tank of fuel, while out moose hunting this year it started using fuel like crazy, 10 to 12 miles per tank of fuel. the machine sounds different likeit has a miss people behind me says they can smell that it is running real rich. any ideas?
 

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Discussion Starter #18
Search on this forum for t-bap harness. I suspect that is your problem.

Stew
 

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it might not be a bad idea to relate the components of an EFI system to a carb unit. basically meaning for instance the Idle speed motor functions but is not limited to the pilot screw on a carb. sure it cannot do this mechanically so it needs other sensors to tell it what it needs as well as the ecu. I mean literally the ISM increases and decreases only air, and the pilot screw increases and decreases actual fuel air but they have the same end result. Thinking of the ecu as your own brain. you would take in data from the crank sensor, air sensor, and tps for instance then your job as " the brain or manager" would be to tell the Idle motor where to be for proper fuel mixture. At the same time " as the brain Manager" you would need to read that crank position to know when to pulse fuel ( used to be done with vacume on a needle jet/diaphram) and ignite fire ( spark ) These things used to be done mechanically with vacume and weights etc. But removing the mechanics created the need for intellegent input of the various parts of any given motor. what used to happen in a perfect balance of mechanical engineering is now a balance of mechanical, electrical, AND computer engineering. So now as backyard mechanics we need and are quite capable of and understanding of how to first test mechanical. this could be as simple as checking plugs to testing the mechanical movement of the ISM, or the out put of the fuel pump spray pattern of the injectors etc. then comes electrical. this includes multi-meter work knowing the proper volteges of each mentioned component what pins to check etc. the simplest I think is code reading of the ECM itself.
 

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Help Needed

So I have been reading all of these posts. I have a 2006 Sportsman 500 EFI. I don't ride it that much. It's been sitting in my shed for a few years, but I start it up 2 or 3 times a month and ride it around for about 30 minutes or so. I also add Staybil to the gas. Not too long ago after riding it one day, I let it rest a few days. Two days later it would crank but not run. I figured it would be bad gas so I drained all of the gas. I also bought a new fuel filter. It still wouldn't start. It will crank but won't run or idle on its own. I checked the fuel injector. It wasn't spraying correctly so I bought a new one and just replaced it today. I also drained out the recent gas and put in 3 gallons of premium. It gets good fuel spray but still doesn't run. I thought it could be the spark plug but it gets good spark when I test it. Cranking is not an issue. I am using a gel cell battery. Carburetor looks clean, removed the AMS sensor - that looks ok too, the fuel rail is clean. I tried starting it with 1/4 throttle. It started a little bit but wouldn't run on its own. I constantly had to pump the throttle to keep it running, barely. When it would not start, I stopped cranking it and there was a slight black smoke coming from the carburetor without the airbox on. Cranking and power, I believe, is not the issue. Any thoughts would be helpful since I don't know much about atv's.
 
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