Sorry, bit of an epic this one but stick with it coz it has a happy ending....
This story starts when I carried out some “winter servicing” back in February this year on my 1999, 90,000 mile 1150GS. All the usual things were done, valve clearances, spark plugs, fuel filter, air filter & also at long last I changed the throttle cables & fitted a new battery (how smug I felt carrying out this work as the snow lay on the ground). In addition to this, the fuel consumption had recently increased & leading up to Christmas I’d attempted to solve the problem by systematically swapping the Lambda sensor, the air temperature sensor & also whilst the tank was off during the maintenance session, the oil temperature sensor was also changed. Anyway after the said maintenance was carried out I went for a test ride for around 120 miles (the weather had improved!). The bike ran really well & the icing on the cake was the fuel consumption had improved and returned to normal. And then it all started going wrong..... A day or two later a slight misfire developed which worsened. This only occurred when under load, say when overtaking or pulling up a long hill. It was more like a four cylinder engine running on three, not as bad as a twin running on one. The bike would tick over nicely, the throttles would balance fine – the fault only showed up when the bike was ridden. After checking & rechecking all the work previously carried out the following list is some of the actions I took through the month of February to try and resolve the misfire (not necessarily in this order!) each followed by a rather frustrating test ride:
New throttle cables checked, swapped back the Lambda, air & oil temperature sensors, changed the coil, hall sensors, new HT leads & to rule out the fuel pump, the fuel tank was swapped, (from a fellow Tosser’s bike at 11PM at the West Mids meet – top marks to Bobble – beyond the call of Tosser duty
assisted by half dozen or so headlights illuminating the scene – a belated thanks peeps 
), I continue: parted & cleaned all the electrical connections under the tank, bridged out the alarm, bridged out the side stand switch, removed the Techlusion, checked the VCU multi pin connector, sprayed the inlets with oil / grease in case of vacuum leak, checked the TPS voltages & ran injector cleaner in the fuel. Although I was getting really good at removing & refitting the fuel tank 
the problem was still there and if anything getting worse. I was reaching the end of my tether and as I began to write off February I thought I would try one last thing. A used injector was purchased from Motorworks (around £20) - I didn’t really think this would make any difference as I had already tried spraying the injectors onto cardboard & the pattern seemed OK to my “untrained eye” (point of note
), and anyway you don’t hear much about injector problems…do you? I was getting desperate! The injector arrived & installed on the RH intake (this side had looked slightly dirtier than the left during my investigations). And, you’ve probably guessed it - the next test ride proved that this was the cure (I’ll have to break for a minute – I’m filling up now
).
To conclude: So although my experience told me that the problem would almost definitely be something to do with what I had previously meddled with, in this rare case it wasn’t! I guess it is possible that a minute dirt particle could have entered the fuel system when I changed the fuel filter but I feel this is most unlikely because I reckon it would have shown up immediately, not 100 + miles later….. Obviously all the bridged electrics & changed sensors were returned to “standard”, Techlusion refitted etc and a precautionary change of the LH injector was carried out. Happy to report the bike has been running as sweet as a nut since, taking a 2000 mile June trip to France in its stride. Oh, and by the way – the fuel consumption increase was due to a failing oil temperature sensor.
So that’s it really. Sorry it’s taken a while to get round to posting this up but its taken time for me to be able to talk about it
Many thanks to my GS riding buddies for all their suggestions (some more useful than others 
) and also to this site where numerous searches lead to another path of inspiration......
In hindsight: I wonder if plug in diagnostic equipment would have pointed directly to the fault – but I figure that would have been much too easy & I wouldn’t have learned so much
I have one question for you knowledgeable peeps on here: Do fuel injectors generally wear out, block or just pack up?
Off for another session at the therapist now………
This story starts when I carried out some “winter servicing” back in February this year on my 1999, 90,000 mile 1150GS. All the usual things were done, valve clearances, spark plugs, fuel filter, air filter & also at long last I changed the throttle cables & fitted a new battery (how smug I felt carrying out this work as the snow lay on the ground). In addition to this, the fuel consumption had recently increased & leading up to Christmas I’d attempted to solve the problem by systematically swapping the Lambda sensor, the air temperature sensor & also whilst the tank was off during the maintenance session, the oil temperature sensor was also changed. Anyway after the said maintenance was carried out I went for a test ride for around 120 miles (the weather had improved!). The bike ran really well & the icing on the cake was the fuel consumption had improved and returned to normal. And then it all started going wrong..... A day or two later a slight misfire developed which worsened. This only occurred when under load, say when overtaking or pulling up a long hill. It was more like a four cylinder engine running on three, not as bad as a twin running on one. The bike would tick over nicely, the throttles would balance fine – the fault only showed up when the bike was ridden. After checking & rechecking all the work previously carried out the following list is some of the actions I took through the month of February to try and resolve the misfire (not necessarily in this order!) each followed by a rather frustrating test ride:
New throttle cables checked, swapped back the Lambda, air & oil temperature sensors, changed the coil, hall sensors, new HT leads & to rule out the fuel pump, the fuel tank was swapped, (from a fellow Tosser’s bike at 11PM at the West Mids meet – top marks to Bobble – beyond the call of Tosser duty
assisted by half dozen or so headlights illuminating the scene – a belated thanks peeps ), I continue: parted & cleaned all the electrical connections under the tank, bridged out the alarm, bridged out the side stand switch, removed the Techlusion, checked the VCU multi pin connector, sprayed the inlets with oil / grease in case of vacuum leak, checked the TPS voltages & ran injector cleaner in the fuel. Although I was getting really good at removing & refitting the fuel tank the problem was still there and if anything getting worse. I was reaching the end of my tether and as I began to write off February I thought I would try one last thing. A used injector was purchased from Motorworks (around £20) - I didn’t really think this would make any difference as I had already tried spraying the injectors onto cardboard & the pattern seemed OK to my “untrained eye” (point of note), and anyway you don’t hear much about injector problems…do you? I was getting desperate! The injector arrived & installed on the RH intake (this side had looked slightly dirtier than the left during my investigations). And, you’ve probably guessed it - the next test ride proved that this was the cure (I’ll have to break for a minute – I’m filling up now ). To conclude: So although my experience told me that the problem would almost definitely be something to do with what I had previously meddled with, in this rare case it wasn’t! I guess it is possible that a minute dirt particle could have entered the fuel system when I changed the fuel filter but I feel this is most unlikely because I reckon it would have shown up immediately, not 100 + miles later….. Obviously all the bridged electrics & changed sensors were returned to “standard”, Techlusion refitted etc and a precautionary change of the LH injector was carried out. Happy to report the bike has been running as sweet as a nut since, taking a 2000 mile June trip to France in its stride. Oh, and by the way – the fuel consumption increase was due to a failing oil temperature sensor.
So that’s it really. Sorry it’s taken a while to get round to posting this up but its taken time for me to be able to talk about it
Many thanks to my GS riding buddies for all their suggestions (some more useful than others ) and also to this site where numerous searches lead to another path of inspiration......In hindsight: I wonder if plug in diagnostic equipment would have pointed directly to the fault – but I figure that would have been much too easy & I wouldn’t have learned so much
I have one question for you knowledgeable peeps on here: Do fuel injectors generally wear out, block or just pack up?Off for another session at the therapist now………
