Did you guys ever find the culprit on this?

 

He has not found anything as of this week. Going to pull the tank and check wires going to injectors tomorrow.

 

This post is information that I am giving those who may need it as an alternative to check if this problem occurs. I am no Harley factory mechanic and I am not attempting to bash any here. Just telling it like it came to me and what i found that solved the problem.

Symptoms:
idles fine, no check engine light, bucks and backfires between take off speeds and 65-70 mph.

2 Harley Dealers unable to resolve issue in two separate states on two separate rides. Things they tried. Blamed Power commander and changed it out twice. Changed Engine temp sensor. Changed Plugs. Flushed tank and cleaned injectors. During this time Power Commander was discontinued and bike owner was charged to install Harley Chip at owners consent on second ride. ECM was burnt up during dealer work 2nd ride and exchanged by Dealer at no charge. All of these things done put a band-aid on the problem for 200 miles and the issue returned. Most would just say bad Gas.

What I found: Disclaimer :I am an independent old school shade tree harley mechanic with no factory training at all who learned from the same.

First thing I did was understand that there was no check engine light and neither of the factory dealers who hooked the thing up to their computers could diagnose with a computer, the issue.

Bucking, Loss of power and backfiring at times through the intake to me mean too much fuel to the cylinder.

Put the bike on the lift and took a look at the color of the exhaust pipes at the back. The right pipe was darker than the left. To me this means that the front cylinder is running richer than the rear.

Pulled the plugs, Rear was perfect and the front was wet. To me this means that either the front isn't firing or its getting to much fuel to burn. Now keeping in mind that the bike idled fine and under load at 70 mph ran fine based on rider complaint, getting too much fuel at mid range. No more power commander so it wasn't a rider setting. ECM programmed by harley very recently and dyno'd so all that's good. I'm pretty sure its firing or their would be a code so pulled the plugs and turned over the bike and they fired. Ohm'ed the plug wires and they were within specs per the bike bible.

So too much fuel, no code. Fuel pressure is within regs per the bike bible and the dealer. So my research concludes that Harley Delphi Fuel Injectors have both an electronic side and a manual side. The electronic side works like an electromagnet as I understand. Constant 12 volts is my understanding and the opening and closing is managed by the ECM telling the magnet to go to ground. So whats the magnet pulling on; A spring. The top of the injector where it accepts fuel from the fuel rail has a screen insert which is like a second filter. Under that is a spring which sits on top pf a brass tube that slides inside the stainless steel injector body with a port through the center that i figure allows fuel to pass to the pintel. The brass also fits inside the pintel to guide the pintel which is also stainless so probably raised and lowered by the magnet, looks like a small cup with holes at the bottom, right before the fuel is forced out the end of the injector into the intake to mix with the air and be pushed into the cylinder to be fired. So metal parts against metal parts create friction which induces wear. Softer metal such as brass wears faster than stainless steel.

60,000 miles on the bike at near 70 mph or 3000 rpm means to me that the injector is firing 1500 times a minute on that cylinder at that speed. Give or take, I'm no engineer but you get the idea.

Changed out the injectors basically and the problem was solved. The front injector was bad in effect the inside was worn and allowing fuel to leak into the cylinder. I changed both just because if ones bad then the others close i figure. Its been there at least as long as the other.

Why? Well in my non expert opinion when you start the bike and its cold it wants more fuel so the fuel leaking past inside the injector was ok. Not causing noticeable problems yet to the rider. Rider takes off and throttles up and the ECM starts to match the air induction with the necessary fuel which means that extra fuel leaking past the injector is giving the cylinder more fuel to burn than it wants to burn and it ends up in the exhaust.Therefore you have a lack of power and backfiring in the exhaust due to the excess fuel burning off in the exhaust blocking the even flow of thermal and sound waves there so the flow is constricted and confused on the front cylinder which I think leads to the spitting back through the intake. At higher speeds of 70 mph and above under load the bike needs more fuel so it starts to even out some I guess and the issue is not a noticeable to the rider.

And Yes after changing the injectors I took the old ones and a hack saw and a vise and verified my theory. The brass inside was worn with noticeable wear marks and not sliding freely with the spring. Starting to slant in the tube some i think, binding. My understanding is the spring is collapsed when the magnet is activated allowing the pressurized fuel to push past the pintel on the other end and enter the cylinder. OOORRRRR more fuel was getting past between the brass tube and the body of the injector than should have been if at all which would mean that the fuel was bypassing the pintel on the outside and wasn't part of the metered fuel entering the cylinder.

In any event the problem was solved by changing the injectors and rider/ owner is happy after 500-1000 miles with no further issues. Seems to me the Dealer should have caught this fuel issue when they changed the plugs but it is what it is.

Hope this helps someone else as I found nothing about it before when i looked.

 

I just accidentally found this and it make a whole bunch of sense. I know it is old post but just wanted to give a thank you to cussport for this post, I think this could be my problem hopefully I will know tomorrow.

 

I'll watch this topic as well for any resolution. mine is an '02 Ultra and been chasing this issue for a few year$ now. intermittent miss, sometimes steady throttle at cruise speeds (65-75mph) but mostly low rpm creeping along like in 2nd gear in town at 10-30 mph with throttle at low opening. I do get an engine light and resulting P 0261 code saying front injector open/low when it happens at cruising speed. going to lift the tank and check the wires going to the injectors for the breakage issue and if no satisfaction I'll change the injectors. pretty much been through everything else with no success.