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I am trying to help a friend trouble shoot his 2009 KFX 450r, it will not stay running at idle. If you start it and immediately give it throttle it will stay running but the second you let go of the throttle it stalls. We have changed plugs, check valve clearances, made sure throttle body is clean, the injectors look clean as well. From what has been described he was out riding, it died and would not restart and has been that way since August.

1. Found an Orange/Black lead under the upper cover, but it is plugged into another wire. Should the self-test Orange/Black lead be just hanging out by itself?
2. When I hooked this Orange/Black lead to the negative terminal on the battery, there were no flashing lights, but the FI light goes out after you hear what I assume is the fuel injector pressurizing, If the ECU has no codes will something flash? Trying to figure out if no indication of codes means all is good or if it means the ECU is bad.
3. Also noticed the decompression spring is not there, I understand this is a somewhat common problem. I assume this is why the starter is having a tough time cranking the motor. Would the missing decompression spring also cause a shutdown at idle?
4. Also hooked up a compression tester, and while cranking got a reading of about 150 psi. Now that seems high compared to other posts I have seen, but I am assuming those readings (around 50-65 psi) are with the decompression system working. Is that a correct assumption?
5. The previous owner removed the airbox and the sensor which is normally attached at the airbox is just hanging there, but I understand it ran before like that, so not sure if that is an issue or not.
6. Also turned the idle adjustment screw counter-clockwise till it stopped and then clockwise for 22 clicks. Not sure if it helped, sounded a little more like it wanted to idle. Also pulled out the knob (choke) and it definitely tried to idle for 10-15 seconds before it died. That is as close to running as we could get it.
I don’t know what else to check, because we can keep it running by goosing the throttle once it fires up I assume it is not a specific sensor (like water temp, etc.) because why would it run at all if that were the case? Any help would be GREAT appreciated.
 

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No flashing = good. If that light flashes it means it's throwing a bad code. Check and clean the air filter if you haven't done it yet and try a new battery ...the kfx's will not run right if there happens to be a dead cell in the battery.
 

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Replace the decomp spring before trying to start it again, 150 psi is too much for the battery & starter to handle, 65~75 psi is normal...!!!

The missing decomp spring can damage your starter & battery...the OEM battery is only 6.5Ah/70 CCAs...

Charge the battery to 12.8 volts full charge, if the battery voltage is below 11.5 volts the ECU & sensors don't function properly...

DON'T JUMP START IT WITH A CAR BATTERY OR BOOSTER CAN DAMAGE YOUR ECU ELECTRONICS
 

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Replace the decomp spring before trying to start it again, 150 psi is too much for the battery & starter to handle, 65~75 psi is normal...!!!

The missing decomp spring can damage your starter & battery...the OEM battery is only 6.5Ah/70 CCAs...

Charge the battery to 12.8 volts full charge, if the battery voltage is below 11.5 volts the ECU & sensors don't function properly...

DON'T JUMP START IT WITH A CAR BATTERY OR BOOSTER CAN DAMAGE YOUR ECU ELECTRONICS
Replace the decomp spring before trying to start it again, 150 psi is too much for the battery & starter to handle, 65~75 psi is normal...!!!

The missing decomp spring can damage your starter & battery...the OEM battery is only 6.5Ah/70 CCAs...

Charge the battery to 12.8 volts full charge, if the battery voltage is below 11.5 volts the ECU & sensors don't function properly...

DON'T JUMP START IT WITH A CAR BATTERY OR BOOSTER CAN DAMAGE YOUR ECU ELECTRONICS
My kfx 450r won’t stay running and my ECU is good, I just got a new one, and my idle is in the right spot and there’s no codes being thrown when I ground it, it runs not so great anymore, and the basics have been covered, (clean air filter, fuel pump filter) I need help
 

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My kfx 450r won’t stay running and my ECU is good, I just got a new one, and my idle is in the right spot and there’s no codes being thrown when I ground it, it runs not so great anymore, and the basics have been covered, (clean air filter, fuel pump filter) I need help
Stock ECU or Procom ECU..??? see pic stock is circled
 

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