fueling fault what could this be.

hi .disco1 3.9v8. just put ecu m8 on and brought up fault fueling fault on n/s bank what could possibly be the fault.car seems to run ok but seems to be heavier on fuel than it usally is.

ok up date on my last post above. i have today pulled each lead off each plug 1by1 and tbh there is very little diffrence when leads are on plug and off plug.you can here the engine change in revs but not loads only a tag on each cylinder. could this be more likely to be leaking valves. the power is there but seams to be very heavy still on fuel and plus this fueling problem on n/s bank. engine starts fine on petrol and lpg.and runs good on both. does have small hesitation on pull off can stall it on both if u dont give a little revs when pulling off. engine has only done 78000 miles which aint a lot.will have to compression test it.any other ideas on what else to check.

MAF sensor if it has one be my guess

the only thing i can think of that might affect just one bank would be the lambda