end of my tether

hi guys can any of you help or advise me im stummped......

i have a 94 v8 disco with lpg, she runs sweet as a nut on lpg for approx 10 miles then i get a misfire, switch her back to petrol and all fine again.
i have changed plugs, leads, dizzy cap and rotor arm but still got this problem.

hope you can give me some pointers

have you got a filter for the gas installed?
Might be that one.

Have you tried to let her idle for some while to see if it's just heat related? Does she misfire on idle after she started misfiring?

the filter is new, i will let her idle today after she has misfried and check this,

thankyou for your prompt reply philvy

let her idle after switching to gas first, to see if she starts misfiring from warming up components of the LPG system.
If she starts misfiring after you switched to gas and let her idle (so, after some time of idling only) it's the lpg system. Most propably vapouriser (rebuild kits available).
It might be that the vapourise is poorly adjusted. My 2.25 had a CONSIDERABLE difference when warm and cold. I could not (like "at all") use the engine under normal temp when adjusted for normal temp, and vice versa, making it a pain (motorway vs town...) This usually showed in lack of power tho (stalled).
How long do you have your lpg system installed? Last check? Recent changes? How do you switch over?

So:
First:
Warm up so you can switch over
switch over in standstill
idle
wait for misfire starting
(if no misfire after "considerable" time, try revving her)

PS Have you changed the condensor?

lpg does need bettter spark than petrol, coil and amplifier can be of reduced performance,check for air leaks ,inlet manifold bolts often become loose etc gas will vapourise easier when hot

Need to check for leaks on all the lpg pipes using soapy water, tighten all clips etc, before you spend any money. Almost certain that the system is running lean.

Worth checking the large pipe between the MAF and plenum for holes, and tightening the clips.

You can also try adjusting the power valve, although this is a very small adjustment.

I've got the leads and software for loads of lpg systems, if you are anywhere near me happy to have a look for you, see what the readings are when the misfire occurs etc.

thankyou wookie, id love to take you up on your offer but your over 200 miles from me, i will try to find someone more local, any offers in south lincs

I had the same problem on a RR ! turned out to be a black box failing ? on my system there was two . one for each bank of cylinders ( can;t remember the name of them ) but as soon as i changed them the problem was gone ...

Find out as much info as you can on the manufacturer of the lpg system and post it here.
Also have a look on the water hoses etc for dates.
I'll see if I can find someone for you.

phone this guy 01933 682189 (he is very good )

once again chaps thankyou for your responses, i will check your suggestions at the weekend when i have time to commit to it,
i did notice however last night that my lpg tanks were low on gas and indeed run out of gas 1/4 mile from home, guess what no misfire at all, im thinking that with the reduced pressure she ran ok, could it be that she is running too rich or am i clutching at straws?