disco v8 auto on lpg fuel probs???

got a 95/96 disco 3.9 auto runnin on lpg ( yes i know im a tight git) had it for 2 yrs and just started having petrol problems... 11 months ago fuel pump went down aa towed me home and i replaced it!!!
all was fine till 4 weeks ago when it just refused to start!!!!
put a few gallon of petrol in and still wouldnt start so called the auto electrician who hard wired the pump to get it to his shop and replaced the yellow fuel relay!! all was well kicked up ok clicked onto gas no probs.... then i lent it the wife who ran it out of gas and clicked it to petrol.... it will start and run ( sometimes) but it kangaroos and just seems to cut out then cut back in???
checked this site and ran through all the forums it seemed like immobiliser problems spider i thought!!!
having just had all the dash pulled out and one fitted at my landy specialist i thought the problem would be solved so ran it all this morning to make sure its reliable and.... its not!!!!
its had a fuel pump as i say, ive also replaced the fuel filter both the fuel relays ( yellow and aluminium) and had the spider bypassed... i am now at a total loss as to what the problem is and how to fix it and would be grateful of any advice
as an after thought my local landy specialist tried to talk to it via diagnostic the abs and srs would talk to them but not the ecu for some reason!!!
is it the ecu or is it something to do with the lpg ?????

what do you mean when you say it cuts out and then cuts back in?

its as though the immobiliser kicks in !!!!! although it has now been bypassed???
it either judders like its on kangaroo juice when setting off or when its on the motorway its like the fuel pump is shut down for a second or two then it comes back to life!!!

thought it could be coil probs but its runnin fine on lpg so there is deffo a spark
its got to be electrical???? and thats where i get lost if i cant hit it with a hammer im flumoxed ha ha

changed the battery now as it was turnin over slow in the mornings and although i was getting ignition lights i wasnt getting lights on my gas switch/gauge.... drove it round all day on petrol...and the problems still there..it still seems to be dying then coming back to life!!!!
ecu????

have you tried checking the alternator charge?

Check your earth straps too.

I'd also look at the petrol pipes, fuel filter, the fuel pick-up in the tank and the sedimenter. If it's not been run for a while on petrol it's likely that there's sh1t in the system, dust/spiders/bats whatever. Might need flushing through somewhat, and at the least probably a new fuel filter.

Paul D said:

I'd also look at the petrol pipes, fuel filter, the fuel pick-up in the tank and the sedimenter. If it's not been run for a while on petrol it's likely that there's sh1t in the system, dust/spiders/bats whatever. Might need flushing through somewhat, and at the least probably a new fuel filter.

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I was thinking along those lines too except that it does it on both petrol and lpg.

" but its runnin fine on lpg " ... made me think it's running poorly only on petrol, hence all the fuel line issues ..

Paul D said:

" but its runnin fine on lpg " ... made me think it's running poorly only on petrol, hence all the fuel line issues ..

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Yep, yer right. Reading the first post made me think it was playing up on both. The more erecent post says that it runs fine on lpg.

Check through yer fuel system on the petrol side. I'm surprised your 'landy specialist' didn't either fix it or point you in the right direction.l

I found a rotten breather pipe and a seal gone round the filler on mine that let in 40 litre of water into the tank.needless to say it wouldnt run on petrol.I took apart the fuel lines tank to engine and they were caked.I also reckon that because it was on gas so much the petrol in the tank went ****e and also didnee help cos i left a £10 in there fer 6 months..

all the fuel pump, fuel filter has been replaced and its all pumping well plenty of pressure through the lines alternator is kicking back a healthy amount of juice so thats not the problem..... was thinking about the engine earth strap as this reminds me of a similar problem i had with my old saab turbo.... all the symptoms led me and my "specialist" to thinking it was the spider which we have now bypassed and yes there is evidence of dry solder on it...... would the spider problem stop my alternator from recharging the battery when the problem is happening????
any how ive now replaced the battery and satdy im hoping my specialist will finally sort this problem out once and for all...
think ill check the earth strap my self tommorow is it just a big woven wire strap from the block to the chassis like it was on my saab????
oh and thanks for all the advice from everyone!

ha ha ha had to laugh at the £10 worth of petty left in the tank for 6 months... and im glad to say im not that tight i regularly run it on petrol for a few miles a week so that nothing rots and it lubes the system
fingers crossed that i can get it to talk to the diagnostic and cure it as it would be a shame to bit her for parts to get my money back for the next one!!!