Howdy Boys, HD techs stumped? I have a 1999 FLHTCUI with 71k on it. Per the HD techs I installed a new crank position sensor(no change). The problem is it misses(intermittently) with flame in the intake as soon as I open the butterflies. It's not throwing any codes. Now they're telling me might be the bank angle sensor. I really cant afford to finance their guess work, know what I mean. Any suggestions would be greatly appreciated.

 

backfire in the intake is one of the following in order of likelihood.

too lean mixture ( at that specific rpm)

too advanced timing

(---------- when the throttle is whacked open the timing should retard & the mixture should get richer like what an accel pump does on a carb bike. so these 2 can be inter-related...a little bit of both, not one or the other )

pushrod/ bent valve, cam timing or other valvetrain problem which has valve open or partially open at the wrong time.


so there is the theory- look at intake leaks.

try to determine under what conditions does this happen...does it only happen off idle or at higher rpms.

valve train problems can be checked by a leakdown test, same as any other 4 stroke motor


Mike

 

thanks Mike, The miss/backfire is intermittent. I'm not a tech by no means. A mechanical problem ie bent push rod, bad intake valve I would think be consistent? this only happens when I just come off idle when it's cold. I can also feel it cruising, (intermittent) throughout the rpm range, worse in the lower rpm range of 2100 or so. What's telling the plugs to fire before the intake valves are closed all the way is what I'm thinking. TPS, the HD tech said maybe the angle bank sensor? I already replaced the crank position sensor per his advice to no avail. I just can't afford to finance his guessing game

 

Oh, also sprayed the intake with either, nothing.

 

if you are getting a 'stumble" at various rpms and conditions then I would look at fuel pressure/volume.

and to tell you the truth I stayed away from efi bikes until the 2009....I didn't think the systems were near as good as they should have been.

Um, carb conversion is what I'd do if someone gave me a magnetti marelli bike.

that's all I got.

*** and I know that some guys here have had great results with the MM efi- so keep this on the front page...



Mike

 

With 71k on that engine if the cam-chest has never been opened and tentioners replaced, thats where I would start looking first, if the tentioners are worn badly it is possible that it has jumped a tooth or 2 on the timing. From your description it tells me that the intake valve is being held open during combustion and igniting the fuel being sprayed into the intake by the injector. I would also pull the rocker box tops and check the rockers and pushrods.....Just my thoughts.