Help!!!!!!!!!!!!

I have an '89 Range rover se.
LPG conversion done last month.
No probs until 28th Dec.
Left work,fuelled up,car started running rough on gas and fuel,cutout but started again. Ran rough all way home,didnt like gas at all.
Next day started it up (On petrol)but it still seemed rough so drove in drive and left it(Was going on holiday that day). Came back week later,never started since. Fuel getting through,spark present but wont fire up.
Wont start on fuel ,wont start on emergency gas start
Other strange thing was that Revs dropped to around 400rpm
Phoned nice man who put gas in but he wont look at it unless I can prove it is a gas problem.
Prior to gas being installed, changed coil,leads,distributor cap,rotor arm,plugs(At nice gas mans request)
Also recently had main fuel relay changed and left injector bank fuel relay changed
Read articles re; flooding. Could this be cause?
Anybody any ideas where I should start? Really lost now.
Thanks

pull the fuel pump fuse out and crank it over on the starter for 10 seconds. put the fuel pump fuse back in and try and start it. if it was flooded it shouldnt be any longer and should start.
i'm guessing this is the 3.5 V8 engine? not sure what idle control system it has so i'll get back to you on that one.
With the work that you say has been done being so recent, i'm inclined to think its something there to be honest, could be a sticking fuel relay. you sure they're all clicking when they should be. try giving them a persuading whack.
i'd check the timing over too. never know! if i remember correctly the gas system needs a different timing setup over the petrol one.

Info/advice seriously appreciated,thanks.
Will take steps suggested and see how it goes.

Will post results, thanks again.

I'd say that since it started after the guy put the gas in that it is up to him to prove it is NOT something to do with the gas converstion rather than the other way around! If he won't look at it, get another LPG specialist to. If it turns out to be an LPG problem then give him the chance to fix it (in writing) if he refuses get the work done and take him to small claims to recover the money.

I've heard a lot of problems with cars after LPG conversions, that's why I wouldn't touch one.

Matt

Going to take the steps MeLLonStu suggested first.
But after that,if no joy, going to take your route(Had already started thinking that way)
Thanks for advice though,kind of verifies what I already thought.

Check air intake due to backfiring many lpg conversions have a fail safe rubber gasket that will blow out before damage to computer fuel injection happens, our discovery had this and blew we had to replace the rubber gasket. Without this the car will flood and not start. Hope this solves problem.
The rubber gasket will be after air filter/computer and before lpg injector nozzle, either a hose type or flap type.
Normally orange in colour.

Thanks to everyone for their help.
Cant buy you all a beer so will give you a laugh.
Finally got the mare going after a month.in that month............................disconnected gas.......still no luck.
Got mechanic to have a look.he had it for a week...no joy.brought it back.
Got a number from mate for somebody else....he had it 2 hours and had it running, albeit a bit rough...............everything that could be set wrong was wrong(Not my doing) timing out ,mixtures wrong. He kept it another day,sorted out distributor, re-positioned gas pipes, replaced safety band (This had already been previously offered in response to mail on this site.) Turns out (Apparently) biggest problem was that when I changed leads,distributor cap,plugs rotor arm(At p.i.t.a. gasmans request prior to fitting) The rotor arm was not an original landrover part(Bought for car accessory shop) anyway,turns out it didnt work properly and he informed me he has had quite a few rangerovers with same problem to the degree he has contacted manufacturers to complain.
Anyway it is going again..............................but Yeah! guess what. still not right. Runs great on Gas, starts great on petrol but after about 2 minutes , stop at a junction, tickover becomes erratic and cuts out. Re-Starts fine. Heat it up ,flick on the gas and it goes great...............The saga continues.............................................Ever get the feeling your chain is being yanked????????????????/