Engine misfires at low speeds

[classic02]

Just pulled the TPS - the shaft appears solid and I can't detect any slop in it while moving the throttle. To my eyes the TPS also looks/moves OK, but guess it still could be an internal issue with it.

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I did a resistance check on the TPS (measured across pins 1 and 3). Not sure I did it correctly, but the resistance appeared to increase very smoothly from closed to WOT position (checked carefully a couple times in the low end of the range where I am having my trouble). Would this say my TPS is OK or is there a better way to verify. I also inspected my IAC - it looked clean, but I cleaned it anyway (little carb cleaner and low pressure air) and got just a small amount of black material to come out the other end on a cloth.

 

[classic02]

Dealer checked my fuel pressure (n/c) - said it was stable at 57 psi @ about 2500 rpm (can I assume this rules out any problems in the fuel delivery system?). However, before this I noticed the bike was running better when I rode to the shop. The misfire was much less (still could detect a little bit), but when rolling the throttle it never started to cut out or belch throught the intake like it has sometimes. The only difference was that I had the TPS off the bike to bench check the resistance and had also I sprayed a little cleaner throught he IAC. The IAC did not appear that dirty so I am wondering if there is something going on with the TPS (price is $37 at dealership).

 

[Jack Klarich]

Dealer checked my fuel pressure (n/c) - said it was stable at 57 psi @ about 2500 rpm (can I assume this rules out any problems in the fuel delivery system?). However, before this I noticed the bike was running better when I rode to the shop. The misfire was much less (still could detect a little bit), but when rolling the throttle it never started to cut out or belch throught the intake like it has sometimes. The only difference was that I had the TPS off the bike to bench check the resistance and had also I sprayed a little cleaner throught he IAC. The IAC did not appear that dirty so I am wondering if there is something going on with the TPS (price is $37 at dealership).

That sounds OK, you have a pressure regulator and a TPS pretty simple system have a look here it will explain how it works Harley-Davidson Motorcycle Fuel Injection Explained

 

[Amish Hawg]

Out of curiosity, are you up and running as usual? I see where there was still a little misfiring. Just curious what was done IF anymore was done.

 

[R_W_B]

Out of curiosity, are you up and running as usual? I see where there was still a little misfiring. Just curious what was done IF anymore was done.

He hasn't been on since Apr 11th, 2012. It may be awhile before he responds. This has been a good thread.

 

[classic02]

I have been on vacation for a week, but have been checking in on the forum every couple of days. I have not had time to do much more work on bike, but I have had it out a couple of times and it is still running "better" as I had shared before (after taking my TPS out and reinstalling it). It has some sputter left in the mid-range rpm, but it hasn't been coughing/cutting out (TG - real pain when starting to accel thru a corner!). The other thing I notice is that it seems better with colder temps (60-70deg) - curious what will happen when I take it out on a 90+ day.

Dealer firmly believes that I need a super tuner installed so they can fine tune the specific rpm where I am having my trouble. Anyone got any thoughts on that vs. my simple DFO now in the bike?

 

[Hoople]

There is a "transition" pot on the DFO you may try adjusting. If that did not help, I would remove the DFO as a test to see if the bike runs better.
The SEST is going to cost a bunch because they will be adding dyno time to it. Plus there hands are tied with A/F ratio. I would not go there.
Take out the DFO and install a TFI would be my next move.

 

[Hoople]

Read the 1st line of this PDF about the DFO. The DFO may adjust similar to a TFI. Very possible you could only need an adjustment.

 

[classic02]

Yep - my understanding from the custom chrome tech guy I talked to is that the DFO should be similar. I had already tried some adjustment with the pots on the DFO and the dealer also made signifcant change on the transition (yellow) pot to richen it up. I can't really see much difference. Before, when I unplugged the power to the DFO to see if it was causing the trouble, the bike still ran at least as bad in the same rpm range and had similar hiccups sometimes when rolling the throttle. I did notice the idle rpm dropped off a little without the DFO so at least it was doing something, but I would think I could tell more of a difference when riding.

 

[Hoople]

but before I start making a mess with WD40 to check it out, wanted to get some feedback.

Be careful with just unplugging the power and thinking it returns the bike back to factory stock. In some cases it can be true and in some cases it may not be. The injector signal may not just "pass through" the unplugged device in its natural state..

You need to rule some possible issues. You may also want to try looking for air leaks using the propane enrichment method. It is less messy than the WD40 way.
A leak could be the reason for the plugs looking like they do. And a small leak won't destroy the quality of your idle.