I have a 1340 cc 1995 fuel injected ultra classic. 22,000 miles. It has been upgraded to a stage II programable ECM, SE-3 cam, SE-intake, SE performance mufflers, Stage II (red) injectors, SE heads, adjustable pushrods, and PC-IIIr. It ran with these mods for over a year with no problems. It has now developed an intermintent
stumbling, missing, hesitation that seems to occur only when the engine is hot and well below 3000 RPM. When hot it will often cut out at around 2000 RPM or lower. I say 'often' because sometimes it runs perfectly. If I am out on the highway and running at, say, 3000 RPM it always pulls and runs normally. Rolling on more throttle at that speed results in normal acceleration right on up to 90 and above with no problems. It's when I come on down to around 2000 RPM that the engine may suddenly start to miss and hesitate badly. No backfiring through the pipes but sometimes spitting back out the intake. At the same time the tachometer will go wild, falling to zero then suddenly jumping to 3 or 4 thousand. If I don't do anything the engine will die, but after stopping can be restarted immediately and idle normally. If I start whipping the throttle when this missing starts I can keep it running by getting the RPMs back up to about 3000 and keeping them there or above. After about 30 seconds of keeping the engine at a very high idle (3000 rpm) the problem will sometimes disappear and the bike will idle back down normally. The tach will resume normal operation too. Taking it back up to speed out on the highway, then slowing back down to around 2000 RPM starts the whole thing over again. Usually.
My shop mechanic has replaced the crankshaft position sensor and it ran about 200 miles with no problems then started it again. He then replaced the head temperature sensor but the problem is still there. We then removed the PC- IIIr. Problem was still there. I'm guessing maybe the the throttle position sensor but we haven't replace it yet because his past experience has never shown a TPS to give this type of problem. Could the new crankshaft sensor have gone belly up this soon? This is starting to eat me up at the rate of about $180.00 everytime we try something new. Can anybody shed some light on my situation? I'm afraid to get this thing into heavy traffic for fear it's going to get me killed. [>:]

 

i have a similar problem with mine, it will stumble and fart through the aircleaner, and buck and jerks at low rpm, i can reach down and tug on the tps harness and it will run great for a while then it goes back to the sos. then i tug on the harness again and its good to go. im gonna replace the tps tomorrow! it is a pain in the ***!! good luck with yours

 

Your poblem could be caused by one of a few things. The wiring harness under the tank that goes to the injectors is first suspect. There has been a common problem with the wiring inside the insulation breaking from the movement of the rubber mounted engine leading to what you explain here.Idle the engine and move the injector wire mainly on the front injector to see if the engine faulters when you move it. The harness has been strapped too tightly from the factory and this is a common problem. You will not see the break because the insulation is still intact. https://www.hdforums.com/m_66257/tm.htm

The second thing to check is the vehicle speed sensor https://www.hdforums.com/m_75918/tm.htm

Also don't over look this https://www.hdforums.com/m_87261/tm.htm

 

Thanks for the tips. I'll let you know what the outcome is from the new info you've given me. Gotta be something aggravatingly simple like a broken wire. She just runs too good out on the open road

 

Looks like Mikeisglidn just may have the same problem I do. Would you please let me know what the results are after you change out the TPS. Can you get to the TPS without pulling the tank ? These fuelies seem mighty peculiar to me.

 

You can get to the TPS without pulling the tank on most bikes but it's close. You can also test the tps as opposed to replacing it with a DVOM

 

I'm back, did fall off the earth, just had other issues to tend to.

The PC is off the bike now, problem still there. Wiggled the wiring at the injectors and the TPS. No engine stumbling while doing this. Mechanic suggested he readjust the TPS. After he did this the problem has morphed into the following: Still starts and runs great cold. Still runs down the road at 70 MPH without a hiccup. Rolling the throttle off, the tach suddenly and intermintently starts making sudden fluxuations. If I feather the throttle back on, the fluxuations of the tach show to be in sync with the engine completely cutting out then running again. These engine cutouts are just like I had hit the kill switch then turned it back on. They occur at all RPMs but disappear as soon as I feed the gas back on and the engine is under load. I can get the bike hot and motor around the neighborhood at 1500 RPM and within two blocks it is doing these complete cutouts. Sometimes it backfires now and then when the engine cuts out and comes back on. I doubt the plugs, plug wires, are bad. This thing does not run on just one cylinder when it cuts out. Its a complete momentary failure of either the ignition or injector pulses. The erractic tach makes me now lean toward it being an ignition problem. Wouldn't the injectors keep firing their pulses even if the ignition firing pulses failed? Doesn't the tach get its signal somehow from the ignition?

 

I have a 99 Roadking that will surge and stumble (someone shutting off the kill switch and then turning if back on is the best discription of the problem I've heard) after riding at highway speeds (70-80mph) for an extended period of time. If I lay into the throttle it will go away above 80-85mph. But as soon as I slow down under 80mph the bike will buck and surge. I have checked the injector wires, cam and crank sens. wiring, and t.p.s. wiring. Last night I checked the t.p.s. with a DVOM and the voltage will increase at a steady rate with no voids or stumbles in the voltage. I have a t.p.s. and a baro sensor that I was going to put on but TCSTD suggested this could be a lean condition and said to try an TFI unit. I'm ordering one today and let you know if it did anything.

 

Let us know what happned, a PM in case I miss your reply.

 

Thanks bkroadking,

I hate to hear your having similiar problems. This thing is really baffling to me. Everything checks (so far) but the bike still sucks. It would be interesting if you could install a temporary tach on your RK and determine if it is fluxuating with the engine hesitations. No tach fluxuations would seem to indicate the plugs are still firing when it is cutting out and it must be the injection system. I'm no whiz with fuel injected, computer controlled bikes. Too many overlaping things can go wrong that only a diagnostic instrument can find. Man I miss the old points, plugs, and condenser days. It if was getting spark, fuel, compression, and was in time, the laws of nature demanded that it run and no computer could say otherwise.

Like your RK, my old 1995 Ultra pulls cleanly without a miss under accelleration in any gear. Even cruises at 65-70 with no problems.

I promise all of you who have come in to help. I'll let you all know what the final outcome on this problem of mine is, even if it comes to me having to show what a stupid idiot I was all along.