03 Ultra engine missing

Discussion in 'Engine, Fuel and Exhaust' started by coop85, Jul 10, 2011.

  1. coop85

    coop85 Member

    New guy here with a perplexing problem.
    I have a 2003 FLHTCUI that suddenly started to miss at most RPM settings. I have replaced the fuel filter, plugs, plug wires, inspected and cleaned the crank position sensor and tried running the bike with every other engine sensor. When disconnecting the MAP sensor the missing stops and the bike runs well, although not as nicely as with it working. I changed the MAP sensor but no help and the voltage checks good. I ran bypass wires from the sensor terminal to the ECM, no help. I'm about to call uncle but just read about some folks issues with exhaust leaks. I may have a crack in the Y fitting just aft of the rear cylinder. Any chance that can cause an intermittent miss? Last note, it seems to be less of an issue at higher RPM (3,000+) while not under load.

  2. glider

    glider Veteran Member

    The crack in the Y pipe is a good possibility. It's a fairly common problem on the older baggers and should be replaced. Welding is usually a temporary fix and replacement is the way to go.
  3. Hoople

    Hoople Account Removed

    An unorthodox way to diagnose a problem but disconnecting the map sensor is probably telling the ECM to widen the injector pulse width to max which would be adding more fuel. That to me says your fuel pump pressure may be Low. Just a wild guess. Maybe pressure regulator or pin hole leaks,,etc

    You must have a stack of DTC's in the ECM just waiting to get out.:)
  4. dbmg

    dbmg Guest

  5. RibEye

    RibEye Junior Member

    Excellent call, as usual.

    First, check exhaust system, to see if one jug is sooting or heating up one pipe more than other. If so, that jug has the problem. If both are the same, the problem is common to both, then...

    Since simulating high load (disconnecting MAP sensor) makes it run better:

    If codes present, finding cause should be easy (check engine light will indicate code presence: on all the ime if current, off then back on after start if historical for '03 scooters). If no codes:

    If issue is all the time, likely pin holes in fuel lines (inside tank), or stuck pressure regulator. less likely but possible, clogged fuel filter or weak fuel pump. In any case, a fuel rail pressure test should show low pressure. Should be around 58psi if good).

    If intermittent, and fuel rail pressure test shows 'good', likely fuel pressure regulator sticky.​

    Now that I think about it, since you have been disconnecting sensors, you WILL have lots of historical codes in there. These will clear on their own after 50 start/run-30sec cycles, or you can have them cleared at the dealership for a minimum 1-hour labor charge (ouch). If no indications from the check engine light before you started disconnecting sensors, the above will be of some use. If the check engine light was coming on before sensor disconnections, then you will need to clear and read for new codes from here. Codes are your friend.

    Good luck,
    Rich P
  6. coop85

    coop85 Member

    Thanks for all the great responses. I found pretty big crack in the exhaust Y behind the rear cylinder. I replaced the header thinking for sure this was the end of the issue. NO CHANGE! However now the battery has drained to the point where it won't start. I have had it running for fairly short periods over the past week but would have thought some of the runs would have been long enough to keep it charge. I've read in some places a bad regulator could be an issue. Any chances it's that or an weak alternator? Again it could be I've run it down over the past week fiddling with it, I'll charge it tonight.

    There haven't been any check any lights other than those I induced by unplugging sensors. Excellent insight on how disconnecting the MAP sensor would affect things, looks like I came to the right place.

    Any cheap way to run the fuel pressure check? I'm guessing I need some fancy HD gadget but would prefer to avoid that. I guess I could at least go armed with an idea for the shop to start with if nothing else. I changed the fuel filter first and would have thought a bad fuel pump would have still been an issue with the map sensor disconnected, but could certainly be mistaken.

    Thanks again!
  7. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

    It should be there right under the gas tank! Oh, I get it. Its not really missing. It just aint running right. :D

    Great folks here have you going in the right direction and sounds like you have it sorted out.

    Sorry in advance,

  8. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    I know you said you were in the tank replacing stuff, buy I had 3 separate incidence of pin hole leaks in the corrugated plastic fuel tubing in the tank on my '03. Might want to give this a read:

    Harley Davidson Community

  9. RibEye

    RibEye Junior Member

    Bad ground or power connection(s), battery connections, system circuit breaker, or system relay could cause your symptoms without throwing codes. Might not be, but you have no choice but to fix first things first.

    Lets all hope for bad battery connections. Please note that your main positive cable goes to the top of your starter, then is tied back to the system circuit breaker, and is distributed from there. I suggest you pull the primary chain inspection cover and sniff for a burnt wire smell (bad stator).

    Fix the power issue, then, if the missing persists, it can be chased.

    Good luck,
    Rich P
  10. coop85

    coop85 Member

    Thanks again. I started cleaning and checking connections and found one of the terminals on the main circuit breaker was loose. Aha! I thought as when I pulled the breaker out it was clearly broken. I replaced it and...no change.

    I opened the fuel cap and listened to the pump run when turning on the ignition. It runs initially for what seems like it always has to pressurize the system, about a second. No sounds of leaks from the tubing. When I turn off the ignition and right back on again the pump runs only momentarily before stopping so I'm hesitant to think it's a fuel tubing leak.

    At least I've found some things that actually needed fixing along the way but the core issue of it missing/sputtering is still there???????