Missfire when hot

Hi and good afternoon,
just a quick question/problem
My 81,000 miles(GAS CONVERTED) 2003 1.8 has developed a miss fire when hot she will start on petrol and run perfectly when cold but when she reaches temp a miss occures.
Normaly she switches to gas automaticly when warm so will not reach a temp where the miss starts
Because she runs 98% of the time on gas the fault only came to light when I ran out of gas and she switched back to petrol and struggled to get up a hill.
After pluging in a diognostic it shows that injectors 1&4( switching them on and off via the lap top) are affected its not the coil packs they are new.
Is it almost as if its running weak although the plugs are all good shade of brown.
the air filter is a K&N free-flowing gauze in good condition.
The fuel filter in the tank was replaced last year.
I have run a tank of petrol with red x injector cleaner through (I thought gummed injectors) but its still the same.
The problem dose not rear its head when on gas only petrol
Any ideas ?

worth checking temp sensor for ecu fuel is enriched for when engine cold

Not much up on Gas systems. I personally think they are scary to work on


What bout Lambda sensor fault ?

Hi again ,
I replaced the temp sender as suggested and touch wood its seems to have cured the missfire
If only everything was so simple