S3 Misfire

I am stumped by an intermittent misfire on my '03 S3. It misses up to about 3500 rpm and then clears if the throttle is held open or clears if the throttle is backed off. it doesn't do it when cold. I think that it may be heat-related, but I'm not sure. I thought it may have been a duff tank of petrol, but I'm now on my third refill since it started. Sometimes it is much worse than others.

Anyone got any ideas before I go to the triumph dealer and he relieves me of large amounts of cash?

Did you ever suss this cos mine has just started to exactly the same thing?

I am thinking fouled plugs or the fuel injection map.

I will start with new plugs I guess.

[kuhlka]

How many miles since your last oil change? My 03 doesn't like going much longer than 3k miles without an oil change.

Check plugs.

There is always the possibility the map in your ECU got messed up by a low battery. I had to have mine reflashed once over this.

Yeah oil is due for a change and I had a low battery at the end of the winter with the speedo blank thingy and even a bump start!
The low battery hadn't occurred to me as a possible cause as I thought the map reset itself after 6 cold starts. I will see when the fuelling is remapped.

Why would old oil be a problem?

Thanks for your comments tho.

:-)

[martinyoung]

Could well be the IACV.

how's your idle? does it hang before settling?

[Helmet_Hair]

I have a hard time with the idea of the ECM "losing" the map after a low battery situation. The map is "burned" or flashed to the ECM...it's now part of the programming. Can anyone else vouch for this...maybe the Triumph is different, but I don't think so. If that was the case, wouldn't other things also get lost, like the warm-up cycle and throttle position? :???:

[martinyoung]

Don't believe a low battery will lose the ECU map.

Some tunes look at battery volts and cause "stuff" but not a misfire. Unless your battery is that bad that the alternator output is all being sucked into the battery and there is not enough juice left to provide a spark. But that would not be an internittent misfire.

Telling ya - IACV (or coils).

[Buster]

I've recently had a dead battery, I had to push the bike to start.. I't was running bad on low revs, it wouldn't redline in 3rd gear! Only midrange was kinda normal.

Later on changed out the bettery for a new one.. And now it runs like before, perfect, and for sure i didn't loose the tors map im the ECU!

[Punkinwing]

Had that on my '03... The center plug had the washer cocked and rusted causing a mis... Corrected and re-torqued plugs and all was right with the world again!!!

Finally sussed it.. the left had cylinder has had water ingress which could be cos its the lowest one on the sidestand or worse I might have a leak into it from the cylinder block or head. The plug was rusted and arcing I guess. Combustion was fine nice tan colour on all cylinders. Changed the plugs and all seems well.. v flexible and smooth. Just gotta find a way of checking if I have a cylinder head or block leak without stripping it all down.