Sorry, this is lengthy, but I just want to be as descriptive as possible. I acquired a 2003 Deuce with 20k miles on it this fall which had been sitting outside in the parking lot at my work for about two years. For mods it's got a 95" big bore kit, V&H Bigshots, SE 203 cam, SE intake, and a PCIII. I've spent this winter cleaning it up and replacing items that I thought would be close to wearing out if they weren't bad already. I've replaced the fuel pump, filter, in tank hoses, spark plugs and wires, changed all fluids, and replaced the battery.

The bike runs great for the, most part, but I'm having an issue taking off from idle. When I am completely stopped, and the bike is idling, it will stumble and miss when I try to take off like it's down to one cylinder for the first 10%-15% of throttle. Once I get enough speed to get past 15% throttle it litterally snaps out of it, takes off, and becomes completely normal again. I don't have any other issues accelerating or at cruise either. When shifting I can roll into the throttle from 0% and its completely smooth. I pulled the TPS anyways, ohmed it out, and there were not any dead spots or abnormalities that I saw. I also removed the PCIII and that did not improve anything. Ran a diagnostic test with the tripometer button and there are no codes.

This is my first fuel injected bike, so I'm a total newbie when it comes to this stuff, but I'm leaning toward the ECM or the ECU. What is y'alls take, and is there any other tests I can perform before I just start shotgunning parts at it? Thanks.

 

It is not the ECM and throwing parts at it will become very expensive.

If it sat for 2 years outside with fuel in it, and you replaced the pump, filter etc, was that because the fuel went very bad? I have seen lines literally dissolved from phase separation in cases like that.

Anyway, If you did not pull the injectors, you might want to do that and look for an accumulation around the pintles. I would have the injectors cleaned professionally (not an additive in the fuel- but removed and serviced) on a bike that sat with two year old gas. I have seen them where it looks like a plastic type (for lack of a better description) crud accumulates at the pintles and picking it off makes a night and day improvement.

This will most likely be something simple like an intake leak, dirty injectors or something related to the mapping in the PC not being ideal for the low end.

 

while an ohm meter is a good test instrument, it sometimes does not tell the whole story. i would test the circuit as it sits in the machine under full voltage conditions. why?? the ohm meter only tests with whatever battery is in the meter assigned to the task so it can not simulate actual conditions. had to drop out for a few but one other avenue is the IAC. along with mr. ed's advice, a good cleaning of it might help also and if you go that route, just as well the whole throttle body.
auto parts store sell pressurized fuel system cleaners that work extremely well but you have to have the can tap which is sometimes costly but i have a work around but you have to have a slip ring can tap. another thing is the fuel system must have a port to connect to. these are aggressive cleaners and i use them on auto with great success. they also have the reloadable systems which are very expensive unless you do this a lot.

 

Ed, I replaced the pump and lines because I knew the filter had never been changed, and they were cheap enough, so I preferred doing it all at once now instead of piece by piece later. The gas was terrible. After I drained it I tried to use it to start a fire in our fire pit and it would barely light. I took apart the throttle body and injectors today and the injectors looked pretty good. I took a big syringe full of Seafoam and a 9V battery, actuated both injectors independent from each other and they both shot pretty clean streams of fluid without anything that appeared abnormal to me. They also ohmed out exactly the same. I may still send them out because I know a professional will be able to test them under a lot more pressure than I ever could, but that's just what I observed with what I have to work with. I was hoping one of them would spray terribly and that be that be the smoking gun. The intake was pretty oily, the air temp sensor, and IAC, in particular, seemed very oily/dirty. However, I did not see any evidence of vacuum leaks, all of the gaskets and o-rings were in good condition but since they are old and hard I will replace them before I reassemble everything.

I talked to a guy at work today that had ridden this bike before it was parked and he said it started having this issue before it was parked, so I guess it is not something new. As far as the PC map is concerned I changed the map from what they originally had in there because what they had was incorrect for the mods it has. I emailed PC, provided a list of mods, and they said that I chose the correct map for the bike. I don't know if it could possibly be corrupted, but like I said in my original post I completely removed the PC from the bike and that did not make the situation any better.

Bustert you make a good point about testing the circuit while it is all together. Are there any write-ups or how to videos that show how to do this? I haven't purchased a shop manual yet, but I may if they show me how to do this stuff. I can shoot wires, but I don't know what I should be looking for. You make a good point about the IAC also. If it was getting hung open for a little bit that would make it act like it has a vacuum leak I suppose, and like I said, it was pretty grimy and oily. Do you have a method of testing that as well? Thanks guys for the input.

 

as with most all of the newer electronics, redneck testing is falling fast so one must have a scanner. with the scanner, you can see what is actually going on with all the vibration and such. with bit rate sampling going higher practically every day ecu are extremely fast. most scanners can log and plot electrical rate and compared with fuel trim, you can see where the stumble occurs.
if you have a fast digital meter, test the tps output wire as you slowly open the throttle, can be done key on/eng off and running. it should be fairly steady.
a set of noids for the injectors and inline spark testers are a great source also, visual drop out. if your meter does HZ, you can use it on the injector to see if the HZ drops or goes wild when stumble occurs. do not over look the CPS as it too can do weird things.