Thread: My New Disco 94, Help Please

I've recently aquired a RR on gas, and can give you some tips regarding the petrol/gas changeover.

Generally, a 94 v8 will have a simple gas setup, probably with a venturi mixer ring and not a diaphram like you'd see on sedans etc. On my system, the mixer ring is before the AFM, and the EFI is turned off after a delay of a couple of seconds when you switch over ( or start on gas for example) - to account for the time it takes for the gas to travel down the tube from the converter thru the mixer and into the engine. There will be a delay relay somewhere that you can adjust. I've figured that if the delay is too long, the gas introduced into the airflow will cause the engine to stall. Likewise, if the idle gas adjustment is off, either too rich or an air leak (too lean) or a loss of vacuum (ancillaries) which reduces the venturi effect and reduces the amount of gas will do similar things.

Try doing the changeover at 1500/2000 rpm and see what happens. The increase in airflow sucks in gas faster so the changeover point passes without too much interruption. It took a little fiddling, but if I do the changeover whilst mobile, or at RPM over 1500, there is hardly any indication of which fuel you're on.

So give your gas the once over, and maybe give the AFM a clean with carby cleaner, and it should be all good. To check if the AFM is ok, unplug it whilst running on petrol - if the engine runs rough, the AFM is working.

Thanks Langy
I will have a look tonight

Karl

Originally Posted by karljanz

Hi Guys
However the car runs fine on gas but idles badly and stalls when I flick it to petrol.

Karl

Hi Karl,
Does it idle ok when you start and leave on petrol?

Also You need to be reving the engine or driving the vehicle at reasonable RPM if you switch back from LPG to petrol,

The reason is when you flick the switch over, you still have a little gas in the line from the converter and the engine starts pumping in petrol at the same time, it'll run rough for a bit and then clear once it's burnt the left over gas, it's normal as long as it comes good after a few good seconds.

It's the opposite when changing from petrol to gas, it shuts the petrol injectors off staight away, and the gas has to come through from the converter.

As langy said it's better if the rpms are up to do this

Hope this makes

Luke

You probally find the timing is just out for the petrol. it is a common problem peoplw fidle with the timing of the car.

1st Check your plugs and much sure your running the right temp range.
2nd find a good gas guy that does this all the time and you will find he will tweek it a little and it should atrt running nicely again on fuel. They will always cough and splutter alittle on change over but then should clear.

carla

When I start it on petrol as soon as the engine fires I need to flick it onto gas, The car will not idle on petrol at all, Just got in from work and its too late to try tonight so I will give that a crack in the morning. Thanks for your help, This is a great forum and I have learnt loads already

Karl

Check timing, should be around 12degree.
Check fuel is not old.
I would also look for any loose, missing or cracked vacuum hoses.

Most LPG systems have a computer that do switchover automatically.
Turn the key and wait 2 seconds for petrol and the system will than switch over automatically.

Take to a good LPG man. Sounds like timing too advanced.