Here's one for you

[Bixxer Bob]

working on my fuel maps, I noticed that the O2 readings are all over the place.  

Normal voltage for the o2 sensor in air is 0.45 volts.  Mine reads 0.46 so it's ok.  anything lower that 0.45 is lean, over is rich.

As soon as I fire up,  on tickover and warmed up, it reads 0.05 which is just about as lean as it can be.  Now, if I pick up the revs, it stays lean until about 3000revs then leaps to 0.8 or massively rich.  same happens if I give the throttle a big blip lean - rich - lean.

So what's going on?

I'm guessing air getting in somewhere that's affecting only low revs, and the long term fuel trim is making it rich everywhere else.  I could drop the trim (it's at 4% at the moment) to bring everything except tickover back to normal,  but lower than 3.5% it won't tickover.

Much as I don't want the hassle,  I think the headers are going to have to come off to check for leaks in that area.

[Sin_Tiger]

That is suggestive of a leak that gets "sucked" shut as the vacumn increases, I think you're headed in the right direction, it's certainly where I would start looking.

[Bixxer Bob]

Been reading again.  I found a post that suggests almost all FI triumphs are prone to air leaks at the TB to head gasket due to the torx screws being made of toffee.  Slightest leak plays havoc.  It recommends as a first step if you've got surging, erratic tickover, or rich running to take the TBs off and change the gasket and at the same time swap out the screws for high tensile steel allen bolts.  It's the easiest to eliminate so to do it first.  Also,  the "o" ring on the TPS can leak with the same result, so if you have the means to reset the TPS, swap the "o" ring too.

It'll take me a few days to get the parts then I'm going to go for it.

[Bixxer Bob]

Got the gasket today.... a whopping  £1.14!!!! That makes a nice change.  Hopefully get it done tomorrow.

Can't get the O ring tho'  not shown in the parts fiche  

[Bixxer Bob]

Got up ready to do the gasket this morning, only to find I was going shopping instead  

Hopefully tomorrow night... :roll:

[AK Tiger]

I think you'll find that most O2 sensors jump around ... cuz that's what the EFI systems are designed to do.  Max voltage should be just under 1.0 volt and minimum should be close to zero.  Your reading of .800v to .050v are right in the ball game.  When the system is in closed loop (computer is "listening" to the O2 sensor) the voltage signal should be swinging + or - of that magic .450v reading somewhere around 1-5 times per second.

If the reading sticks below .450v and doesn't show rich, suspect a vacuum leak or something that would cause a lean mixture.  If it hangs on the other side (greater than .450) look for something that could cause a rich mixture.  Things like excess fuel presure, clogged air filter, leaking fuel injector(s) are some likely suspects.

Hope this helps.  I've worked on FI systems since the early 70's (thanks VW) and have taught this stuff at the college level for waaaaay too many DECADES!

[Bixxer Bob]

Cheers AK.  I had a bit more of a play tonight and the o2 flips from lean 0.05 volts to rich 0.9 volts at around 2000rpm.  I used the stepper motor manual-increase in Tuneboy to slowly increase the revs.  At about 1950 it started to rise rapidly and by 2000 it was way rich.  I'm pretty sure I'm looking at an airleak in the intake side.  It's just frustrating that I can't get time to do it yet.

o2 is steady 0.45 volts (as it should be) at engine off.

[Bixxer Bob]

More web reading and I learned the voltage flip flop is a symptom of narrow band O2 sensors.  They only show correct fuel (0.46v) lean (near 0v) or rich (near 1v) with nothing relaible inbetween.  I can't get her to run rich at tickover though so still want to eliminate the airleak possibility.

[Bixxer Bob]

Did the gasket last night, only took 90 mins start to finish.  I'll put a few does and don'ts in the knowledge later.

Seems I had a leak although nothing obvious.  Gasket was brittle and stuck to the flanges as you'd expect.  Anyway, ran it up after and it was immediately smoother, not so many stutters on tickover.  then did the TB balance.  Now the o2 stays lean until about 4000rpm.  I really need to get on a dyno or at least an exhaust analyser.

Can't run it on the road until Friday.......