1: It will reveal if a remap is bad and underfueling.
2: It will reveal if your fuel pump is dieing slowly (they tire with age and are working close to max on a 300 BHP engine).
3: It will reveal if you have a fuel pipe leak(!), as the readings will go lean.
4: The readouts can/are used during mapping, very usefull if you have a 3rd party ECU and self map.
5: If you make some mild tuning mods to your car (eg 3 inch tophat change) you can check that your fuel tabs in the ECU have adjusted to compensate.
Of course we all know that driving with a lean mixture is tantamount to ruining your engine. If just a bit lean, exhaust gas temps have a tendancy to rise and power can be reduced. However, if running badly lean then you run the risk of detonation, a catastrophic event that will bugger your pistons very quickly causing many £1000s of damage and most probably write your car off.
With this in mind a few days ago I managed to haggle a local shop down to £148 for a well respected kit from Innovate. Yesterday I got the sensor bung welded in by my friendly local exhaust fabricators (for a £10er which was a bargain as it took 1 hour to do) and today I spent about 6 hours installing it. It is a bit of a fiddly job and requires carefully locating and cutting into a existing (igniton) switched live. I tried to get my switched live and earth from the stero and wasted about 2 hours messing about unsuccesfully with this. In the end I got the live from the rear left of the boot (PICS HERE) and the earth (as recommended) from the engine itself.
Of course you need to be jolly carefull not to mess the wiring up or you will be blowing fuses and possibly causing horrible electrical gremlins in your car. I checked and re-checked my wiring before powering up and starting the calibration. Thankfully it worked exactly as the instructions said and I went out for a gentle blast on my local test-track. Figures on the guage were measuring from 10:1 with my foot down to 14.4:1 when idleing - perfect (thanks to Stephan and more specifically Courtenays).
I felt the kit was very good, the wiring was neat, the instructions clear and every part was included. If you should feel the need to buy a kit I would recommend the Innovate one.
Pip pip VX chums !
Nev.
Edited by Nev, 19 November 2009 - 10:30 PM.
seen that kit before and heard good things 
glad you managed to trace the switched live with my dodgy instructions on the phone LOL
DG
Dont forget too rich means power loss and can lead to bore wash/thinner oil
)
I didnt measure the exact thread of the bung, but I did notice that none of my metric spanners fitted the sensor, so I had to use a monkey wrench to tighten it up. I expect this is cos the Ausies use imperial tools mostly 
not using a very good stable live & earth. Its essential its got a good strong power supply.
The LC-1 is a good bit of kit I run one output as simulared narrow band for closed loop lambda and the other wide band for a gauge and data logging for when I tweek my map after any changes I make to the car. I'm probably going to ditch the gauge when I rebuild my interior as I can set limits in my ECU to put it into safe mod if certain conditions are met i.e. high boost and a lean AFR so I never really look at the gauge anyway.
10:1, on boost they do run pig rich then 11.5:1 should be optimum for boost with safety.
