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Engine misfire under light load

89stroker

89stroker

Active Member
Hello All,
I have been chasing a problem for the last week or so that my 2010 ultra classic will misfire under light load when I am on the highway. The bike has a 103", 255 cams, TFI, de-catted headpipe and SE Fatshotz mufflers. 23,375 miles on the odometer. I thought I could figure this out myself but I am coming the you guys for some possible insight to this.
I have made no changes to this bike for the last 2 seasons. The problem began out of the blue, at first I thought I got a tank of bad gas but I have run that tank out, then I ran a tank with a stiff mix of seafoam though it plus 2 more tank fulls with no improvement.
The bike idles great, pulls hard with no miss, in fact it won't miss at all if I ride into a headwind with some significant load on it. It seems to miss under light load like when I am riding with a tailwind, also when I am climbing a slight incline as I crest the top or just over the top (using cruise control) as it backs off throttle and just starts back applying throttle that's when it misfires. Some times it will just be one miss, sometimes it will miss several times in say a 3 second span.
So far, I have taken apart battery connections at both ends, cleaned and reconnected using dielectric grease, checked all fuses for corrosion (which there was) cleaned and reinstalled all with dielectric grease, replaced spark plugs, inspected plug wires. Tested resistance on ignition coil, reading was 6.23K ohms. I am not sure what this reading should be, I know on older models it should be 10-12.5K ohms. Also checked to make sure gas tank vent is open.
The problem to me almost seems throttle postion related.
Sorry to be so long winded but just trying to give some detail. I am hoping someone can give me some ideas as I have a 10,000 mile adventure planned that is coming up on August 20 so I need to get this figured out.

I should have added that I have not had a check engine light come on. I almost wish it would, maybe that would tell me what is happening here.
 
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Great discription of the problem. I'm totally guessing, but could it be something in/with the "throttle by wire" system? A slight interruption in the signal?
 
89stroker said:
Sorry to be so long winded but just trying to give some detail.
Click to expand...

Heck, don't be sorry. Great info & the more details the better. I would almost bet the farm it is not electrical. The problem is just too predicable and too RPM specific to be electrical. To me it sounds like a lean engine miss during closed loop periods.
Are you still running O2 sensors or have they been removed (deadheaded w/ plugs)?

You said there were no codes. I would expect some sort of code(s) if the O2 sensors were just removed.
 
Breeze3at - Could be throttle by wire, but it does it when using cruise control as well, I use cruise a lot because where I live it is lot of straight road. I wonder if any signal is going though the TBW while on cruise? Thanks for the suggenstion.

Bodeen - I will look at this but I believe my '10 throttle body is different than earlier models but it's something to definitely look for. My manual shows that there is a throttle control actuator (TCA) that operates the butterfly, then a temperature manifold absolute pressure sensor (TMAP) right after the butterfly, then the injectors. I'll look further into this.

Hoople - The O2 sensors have been disconnected but are not plugged off, Doebeck said it did not need the plugs. I have been running it like this for 2 years. I only said I have not had a check engine light, I have not looked for codes as of yet. I am unsure of the procedure as I don't have a diagnostic manual for the bike, would it be the same as the procedure for an '09? I wasn't able to find in my search a procedure for a '10. I'll do a search on best methods to use to check for intake leaks, I've seen WD40, propane, starting fluid, etc. Any suggestions?
 
I'm sure code pulling is the same as a 2009. No harm in trying a WOW test. I would think you will have a couple of soft codes in there. Maybe something like P0134 or P0154 (O2 not responding).

It sure sounds to me like a lean miss (correct amount of air but not enough fuel) and not along the lines of an air intake leak (correct amount of fuel but too much air) because if it was, the idle would not be "Great" like you say it is. Since the idle is good, I would set aside intake leaks for a minute.

I would be looking at fuel starvation such as low fuel pump pressure, bad spray pattern or fuel flow restriction on 1 injector, pin hole leaks inside tank,,,things like that. Something that would make you leaner than needed during closed loop operation (cruise lite load, cresting hill & backing off throttle). Open loop operation (WOT or riding against headwind) can hide a lot of fuel issues because generally open loop is feeding more fuel (wasting) than you really need. There is very little wiggle room when running closed loop with narrow band O2 sensors and E10 fuel. Just about NO wiggle room at all.

I will assume you still have your factory bone stock Maps loaded in your ECM. If that is true, remember 1 very important fact. A TFI takes your current maps and stacks them with a pulse stretcher which in turn adds more fuel. The TFI doesn't know what your starting base maps are. It just sees a value and adds to it. Since your Maps are factory stock, you have to stretch them a bunch. Your stretching them from factory bone stock lean.... to a stock Rich and Happy,,, to a Stage 1 Rich & Happy......to a Stage 2 Rich and Happy. That's a bunch of stretching. It's not like you started with a set of EPA approved Stage 2 maps and your building from there with the TFI. Your building from factory stock maps to a Stage 2.
So it is possible during closed loop map cells, you were right on the edge of needing even more fuel.

I don't own a TFI so I can't tell exactly where to set the pots. But I would push mixture to the rich side using the pot that controls mixture when intake manifold pressure is high (low engine load during closed loop operation). Is there a pot that feeds that mid-range cruise RPM band your having the problem at?

Just as a test to see what the results would be, I would temporally make the mixture really fat by pushing the pots just to see if the engine miss goes away. Then depending on how much you had to push the pots, check the items I mentioned earlier.

Just pushing the pots a little bit may do it. But even if it does,,I still would check fuel pressure/pinhole leaks etc. You don't want to offset the root problem you have but just using the TFI pots.
 
Hoople, I did another search and found a '10 touring models DTC procedure and it is the same as the '09. I just got back from my shop where I checked for codes and you are correct I had P0134, P0154, and P0031 all which are O2 sensor related. I had no other codes. I also checked for intake leak using carb cleaner, I had no increase in idle speed spraying the carb cleaner around each of the flanges.

The map that was loaded in my ECM is for a stage 2, in fact, I had it back a bunch of times for different maps after the stage 2 upgrade as it was pinging. The map that is in there was ok after the dealership got the proper one in there, no pinging but bike still ran pretty hot so I talked to Matt at Doebeck and asked him if I could use the TFI that I had from when the bike was stock 96" and he said absolutely and gave me the settings for it. I installed the TFI and it ran great for 2 years up until it started doing this 1 1/2 weeks ago.

I did look in the fuel tank and turned the key switch on so the fuel pump ran, I saw no spraying inside the tank, tank is only 1/3 full of fuel so if there is a pin hole, would'nt I see something?

You may be right about being on the edge and I believe there is a pot that adjusts mid-range cruise. I will fatten up the mixture like you have suggested and hopefull get some cruise time in (work gets in the way of a lot of things).
 
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I am glad to see your building on a set of stage 2 maps. I am really surprised you had pinging w/ a set of Stage 2 maps. The stage 2 spark advance maps and ion sense knock retard subsystem should have took care of that. But since the bike has been fine for the last year & a half, there's no point in dealing with that question now.

Turning on the key only runs the fuel pump for a few seconds. When I look inside my tank, so many vital parts are blocked from view, that its hard to tell if anything is leaking. I guess if the hole is big enough, you may see or hear it.. just don't know. The best way to test it would be with a fuel pressure gauge. It is too bad you need special fittings to check fuel pump pressure on these bikes. One simple 60 second measurement would test & eliminate several possible issues all in 1 shot. HD does not sell the fitting. "Jims" makes one but the price is far out of reach.You can make one up yourself but it still costs $65 (plus the gauge).

See what effect pushing the TFI pots (making it richer) has on the engine miss. I am hoping you see a change for the better. Then seeing how much you needed to push the pots, you can get an idea where the root problem is.
 
Thanks for all your help so far Hoople, it means a great deal. I will richen the mixture to see what happens and will look for the fittings to build a pressure gauge set up.
 
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