09 UC stumbles below 2700rpm. great above 2700

[B-1B_Guy]

Rode bike for 200+ miles (ran great) and then I stopped for gas Saturday afternoon and that's when it all started. Bike immediately started running poorly at low rpms. It stumbles, coughs and sputters when I roll on the throttle slowly below 2700rpm. Is fine when I romp on it below 2700 and all throttle positions above 2700 are great, bike has no issues above 2700rpms. I figured it was bad fuel. Drained the tank, changed fuel filter, fresh tank of premium gasoline & the bike acts the same. Changed plugs (why, I have no idea), no change. Disconnected the battery for a few hours, no change. Took Power Commander 5 out of the loop and plugged stock ECM (HD download previously loaded) back in, no change. Bike is not throwing any codes. I'm thinking possible throttle position sensor or maybe crankshaft position sensor....

Anyone experience this same problem? I did search and read several threads but didn't find anything specific......

Could use a hand. All suggestions welcome.

 

[Hoople]

Bike is not throwing any codes. I'm thinking possible throttle position sensor or maybe crankshaft position sensor....

At this moment you have the stock ECM in the bike and it runs strong from 2700 RPM to redline. Your bike is throttle by wire, so you actually have (2) TPS sensors that are cross checked with a summing voltage for protection against unexpected acceleration. If either was bad, you would probably know it because the summing voltage would be off.

How long have you tested the bike with the original ECM in it. Have you given it enough time to grab a code. You absolutely have not seen any DTC's while using the original ECM and when you do check for DTC's (using WOW), you see the word "None". If so, I would lean more toward low fuel pressure or the crank sensor. Low fuel pressure will not throw a code, but you will get a serious flat spot,, just like having a bad accelerator pump on a carburetor. The output of a crank sensor could be marginal at low RPM and it also would never trip a code.

Any difficulty starting the engine while Hot? And you have used up enough fresh gas to know for a FACT that the old stuff is long gone.

 

[RibEye]

Also, you could have an intermittent injector connection, and it would not throw a code until it kept the cylinder from firing for a significant continuous period. I suggest a good continuity check of teh injectgor lines from ECM to injectors, moving the wires at the injector ends vigorously. Sometimes the connection only breaks when the engine is vibrating at the lower RPMs.

Enjoy,
Rich P

 

[B-1B_Guy]

09 UC stumbles below 2700rpm. great above 2700

Tank/Hoop/Ribeye,

Thanks for the ideas. I'll start with cleaning the IAC as it sounds the least painful.

To answer Hoops questions. I did not run the bike long with the original ECM, only a few minutes in fact but the bike acted exactly the same as it did with the PCV hooked up. Zero codes. Checked all 5 areas and got "none" for all. Bike starts great, cold or hot. I'm certain all of the old gas was out, rode the bike for 20 miles after draining the tank and changing the fuel filter.

A bit more info. My bike has 33K miles on it and has ran great since I did my motor work over 20K miles ago. Just want to eliminate any thought of an upgrade gone bad......I've had that happen as well.....

Thanks again,

Will keep you posted.

Cleand IAC. Clean as a whistle......did not help the issue. You guys given up on me? Where do I go from here?

 

[dbmg]

This may be completely wrong but could not hurt. With PCV removed and only using stock ECM, disconnect battery for 15 minutes and see what happens...

 

[Hoople]

It stumbles, coughs and sputters when I roll on the throttle slowly below 2700rpm.

For an off idle bog,,,
Big hitters for me would be knowing the fuel pump pressure and knowing if Map sensor was reading correctly. Simple to check with the right tools. Pain to check without them.
TPS if you were not throttle by wire but since you are, I would put that on back burner for a moment.

Either one could do it without ever throwing a DTC code. (You must fix this using the factory ECM first)
With a clear error log, drive the bike repetitively in the forbidden region, & hope you throw a code.

 

[B-1B_Guy]

Hoop,

Stopped at Black Hills HD on the way home from work today and the mechanic said to check the fuel pressure too. With the Sturgis Rally going on here I was shocked they would even take the time to chat about it. I may end up taking the bike in as I don't have the tools to check the fuel pressure. I did check every electrical connection and ground today and didn't find any smoking guns. Still am not getting any codes; however, P is saying "no rSP" no response. I am going to leave the bike sit overnight with the stock ECM unhooked and try it with the stock ECM tomorrow. Not real confident but I'm running out of options here.

I sure do appreciate everyone's inputs. Thank you.

 

[B-1B_Guy]

Alright fellas. left the ecm disconnected overnight and started the bike after work today. same deal, still running poorly below 2700. don't have a fuel pressure sensor but I pulled the fuel line out of the rail put my thumb over the end of the fuel line and turned the bike over. almost blew my fingers off....lots of fuel pressure. prehistoric way of checking but beggers can't be choosers.

so, i'm rapidly running out of ideas.

I do appreciate everyone's help and I will let you all know what fixes it. may be a while.....but I will let you know.

ride safe

jim

 

[dbmg]

left the ecm disconnected

Have you tried disconnecting battery. There maybe parts of the electronics that are not going to sleep.

 

[B-1B_Guy]

Well, it's fixed. Hooked up the laptop to the Power Commander and reloaded the map. She's back to 100%. I guess I should have treated the bike like a computer (reset power and then reload the software) I did spend lots of time chasing my tail but at the same time the bike sure did get a thorough look-over. Good preventative maintenance practice.

Thanks to all for the ideas!