lpg wont rev

[boatboy]

HI
got a bit of a problem with my range rover 3.9 lpg (voltran single point)
its stopped reving over 3000 and really struggles under load.
runs fine on petrol, as i dont have any manuals for the gas bit i am a bit stuck as i dont want to start twiddling with things as i dont know what screw does what.
has anyone any ideas
thanks in advance

[suzukishrek]

Sounds like it's running short of LPG - either literally running out in the tank or the mixture isn't right and it's too lean at the top end. Is it backfiring at any point? When exactly?

If it's too lean you need to get it sorted quickly as you could damage your engine. If you don't know what screw does what I suggest that you get it done professionally as you may make it worse - they're not complicated to be fair and I'm guessing you only have two adjusters. One near the vapouriser and one further down the pipe nearer the mixer. If you can mark where they are so that you can return them to exactly that position then fiddle away.

Before you start fiddling, have you changed all your electrical system for new? LPG is VERY particular about failing plugs, lead and everything else connected with generating the spark for ignition. Petrol is more tolerant of these components beginning to fail.

What about any filter(s) you have in the fuel line?

If you need to start twiddling then, generally you adjust the adjuster nearer the vaporiser first, turning it quarter turn at a time, waiting a couple of seconds between each turn to see what affect it has. Adjust it one direction until the engine starts to run lumpy, then adjust it the other way so that it improves running, keep going until it starts to run rubbish again and then go to a position midway between the two extremes.

Now move onto the adjuster nearer the mixer and do exactly the same thing.

Now repeat the whole procedure at least once more, maybe as many as you can be bothered to do until you make no further difference.

If this doesn't make a difference then you must have a closed loop problem (O2 sensors) but I doubt it as the feedback mechanisms are normally shared with the petrol engine and you say that is fine.

[boatboy]

hi
thanks for the reply
it backfires under load at about 3k
i have changed plugs, leads about 1 month ago
there is a brass screw on top of the vaporiser and a black one about halfway down.
there is also a screw with a spring on the Y piece leading to the injector
Cant see any filters anywhere though
Im quite good with petrol but this gas is a bit new to me and need to know what does what
As far as i know the timing is set up for gas so it runs on petrol ok although a bit lumpy which is normal so ive been told but any advice appreciated as i may have been told wrong.
Its been doing approx 65 miles on a tenner if that gives any clues

[webber1982]

if its just started doing it all of a sudden its probarbly the diaphragme in the regulator unless it has a lambda control feedback system on it then its probarbly the box.

[boatboy]

OK
just had a few hour twiddeling and adjustments dont seem to have done anything
talked to it nicely, no better
swore at it, no better
no trees available to do a Basil Faulty
So will investigate the diapragm (Seems logical as if perforated i suppose it would try to close after the initial surge)