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Discussion Starter #1
I have been on this site for the past 4 months after I bought a 2008 kfx that needed much attention. Here are the mods it has and things I have added that could be related:
FMF slip on pipe
HMF fuel optimizer
Jeep coil upgrade (works amazing!)
New water temp and air temp sensors
TPS set at .63 volts
New battery
Charging at 13 plus volts

Here is the issue. The bike will cut out at higher throttle after I have revved it up a few times. When I first start it I can rev up and the bike rips at all throttle positions, but will start to cut out/backfire after it has done that cycle a few times. I can turn the switch off and the bike will "reset" and will rev again no problem for a few times cycling the throttle at full. This makes me think that it is an electrical issue with the ECU or fuel programmer. I have been slowly fixing aging parts and working at getting the bike working properly. One of the first things I did was replace the water temp sensor and yesterday changed the air temp sensor. I thought the issue was fixed after replacing the water temp sensor and indeed it did need replacing because the fan started to kick on automatically (instead of using the inline switch I added before I knew that was the issue). I mostly ride Michigan 50" trails which are usually slower speed, but would love to take it out on the bigger routes and get some speed without the machine bogging. I played around with the fuel optimizer and can change those settings but it will still have the problem mentioned above.

If this is an ECU issue, would an aftermarket one fix this problem? Is there one that you have liked? I love this bike and is my first one and hoping to make it last for years to come. Thanks for any input.

This post describes my issue as well: cuts out at 1/2-3/4 throttle
 

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I have been on this site for the past 4 months after I bought a 2008 kfx that needed much attention. Here are the mods it has and things I have added that could be related:
FMF slip on pipe
HMF fuel optimizer
Jeep coil upgrade (works amazing!)
New water temp and air temp sensors
TPS set at .63 volts
New battery
Charging at 13 plus volts

Here is the issue. The bike will cut out at higher throttle after I have revved it up a few times. When I first start it I can rev up and the bike rips at all throttle positions, but will start to cut out/backfire after it has done that cycle a few times. I can turn the switch off and the bike will "reset" and will rev again no problem for a few times cycling the throttle at full. This makes me think that it is an electrical issue with the ECU or fuel programmer. I have been slowly fixing aging parts and working at getting the bike working properly. One of the first things I did was replace the water temp sensor and yesterday changed the air temp sensor. I thought the issue was fixed after replacing the water temp sensor and indeed it did need replacing because the fan started to kick on automatically (instead of using the inline switch I added before I knew that was the issue). I mostly ride Michigan 50" trails which are usually slower speed, but would love to take it out on the bigger routes and get some speed without the machine bogging. I played around with the fuel optimizer and can change those settings but it will still have the problem mentioned above.

If this is an ECU issue, would an aftermarket one fix this problem? Is there one that you have liked? I love this bike and is my first one and hoping to make it last for years to come. Thanks for any input.

This post describes my issue as well: cuts out at 1/2-3/4 throttle
Remove the fuel controller. It’s not needed

check fuel pressure or change the filter and pump
Did you use the accel adapter? It’s notorious for causing issues
 

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Discussion Starter #3
Okay I will start with the fuel controller removed. I’ve got a fuel pump and filter coming from eBay that I will try out when they get here. As for the coil, I made my own adapter and used soldered and bullet connectors to attach. I was having issues before I did that upgrade though.
 

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Okay I will start with the fuel controller removed. I’ve got a fuel pump and filter coming from eBay that I will try out when they get here. As for the coil, I made my own adapter and used soldered and bullet connectors to attach. I was having issues before I did that upgrade though.
(stock ECU)
TPS set at .63 volts (out of range causes DFI error/ advance timing is locked) That's a major problem...

Re-adjust to 0.61 DCV motor cold...or 0.62v with the motor warm...

Only with the Procom ecu can you set to 0.63v or more...Not with the OEM stock ECU...
 

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Discussion Starter #5 (Edited)
I tested it again today and it was .60v not .63v. Removed the fuel programmer and tested again and it was .68v so I adjusted it down to .61v. Full throttle was measured at 3.71v. Took it for a ride for about 20 minutes and still had the same symptoms.
 

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Discussion Starter #6
Changed the fuel pump relay and didn’t fix the problem. Still waiting on fuel pump and filter to swap out. No codes coming up...
 

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I tested it again today and it was .60v not .63v. Removed the fuel programmer and tested again and it was .68v so I adjusted it down to .61v. Full throttle was measured at 3.71v. Took it for a ride for about 20 minutes and still had the same symptoms.
When your getting different TPS reading...Make sure there's a little slack in your throttle cable to prevent false TPS voltage readings or bouncing when turning the handlebars...!!

Yea your symptoms are probably a clogged fuel strainer...? If not..check the water temp sensor for being faulty...?
 

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Discussion Starter #8
I had a problem with the throttle cable at first and ran it a while and re-checked. I know 100% I had a bad water temp sensor that I replaced and this one seems to be working (the radiator fan kicks on). Should I be measuring voltage of the output? My problem would be that it is having these symptoms only after a few high throttle revs and I don’t know how to test everything because it resets itself and is fine. The manual says to remove the ecu and test but my conclusion is it’s fine after first starting and is not throwing codes so testing seems pointless. I ordered a Procom ecu tonight as it seems the stock one is fried but I guess it is possible a sensor is bad? Just want to get back on the trails and not blow it up...
 

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The self diagnostic only checks for open or closed shorts in the wiring harness...you'll will need to check the voltage of the sensor to know if faulty or out of range...

Also you can NOT use the Optimizer with the Procom...So remove it when you hook up the Procom...!!!!!
 

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Discussion Starter #10
PROBLEM SOLVED!! It was indeed the fuel pump and filter (or lack of one). I got it taken apart and I was checking for the filter to see if it was clogged but apparently one of the pervious owners had taken it off and not replaced it. 😤 I have not installed the Procom yet but still thinking I will for future upgrades and performance gain. Thanks guys, lesson learned and have a spare pump now.
 
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