Rear cylinder not firing when bike hot

Real strange this. Once I've been running for about 10-15 minutes the rear cylinder starts to miss-fire. This gradually get worse until it stops firing altogether. Tried changing the plugs but this hasn't helped. Bikes 2 months out of warranty, going to ring Leeds Harley today BUT some says it might just be the plug lead???? Any ideas guys??

Its a 2008 FXDF and has a stage one using V+H fuelpak.

[Oilslick]

I had a problem with this on my 06 Dyna.

It started as an intermittant missfire which got worse until it eventually threw up an error code. Something like 'rear injector low/open'. The conductors of the wiring from the ECU to the injectors had broken inside the insulation where it come out of the loom on the backbone.
There was not enough swan neck to allow the engine to rock on the mountings. Had to piece out the break but it's been OK now for another 12,000 miles. I though this had been resolved on later models so may be nothing to do with your problem.

The weird thing is its not throwing any error codes at all! Part of the rear wiring loom dropped down from under the mudguard and the stealers fixed this - having said that the problem started after they had done this so it is possible they have trapped a wire. It only does it when the nike has been running for 20 mins or so thought thats the strange thing!!

[devon.john]

i think its your coil .
it gets hot then brakes down usually about 20 minutes. if you got a frend with the same coil swap and make sure as they are expensive
injection has 4 wires carb bikes as 3 wires,

john

[b0nio]

Does it just misfire at idle and seem ok at large throttle settings? If you switch everything off and then restart the engine does it run ok? If so it may be due the the ECM going into hi-heat mode. Have you got Xeids or 02 eliminators?

No xeids or eliminators - its at large throttle settings that it happens. Got it booked into the stealers on Wednesday. Suspect John's right and its the coil but I'm on hols in two weeks and need it!

Dealer seems to think its probably the fuelpak - and has said they'd try and work something out since the bike is only a couple of months outside warranty!

[Limey_Dave]

I'm with John,my money's on the coil.I don't see how fueling is changed by heat.
If it was starved at large openings,you'd still expect it to tick over,and you'd prob get a code like P0263.

Fingers crossed you get it sorted for your hols.

Well as is usually the case with an intermittent fault the damn thing ran ok to the dealers - but it was peeing it down and I was taking it very steady. Dealer said it was showing that the rear had failed ignition but they couldn't find a fault. They suggested that we take the fulepak out of the loop to test it. I managed to convince them that replacing the coil was the way to go. Having thrashed the tits out of it on the way home no re-occurrence - so it is looking like the coil!!!!

[devon.john]

great as i had this happen a last year i was 99% sure it was coil problems,
thanks for the feed back this is what we must remember todo as its good to for us to know if we are on the right track to solve problems

john

Nope - managed to run for a couple of hours and then away it goes again. Swapped the V+H fuelpak for the SE version - it does seem to be running better now! Anyone know where I can get a copy of the software that reads the tuner - would be interested to see how things are!!