refuses to idle on LPG and returns to petrol

My 3.9 v8 LPG has a Autogas 2000 Tartarini Multipoint injection LPG system. Runs fine but it refuses to remain on LPG while idling in traffic etc waiting for lights etc and returns to petrol....I accelerate away and it returns to LPG....it used to idle perfectly on LPG so I can't understand why this is now happening.

Any suggestions.


Craig

This may or may not help.... My L322 usd to drop out of LPG mode for what seemed no apparent reason. Went back to the fitters - who plugged it in and diagnosed a faulty temperature sender, fitted an new one - no more dropping out. Hope this is useful.

forthbridge said:

This may or may not help.... My L322 usd to drop out of LPG mode for what seemed no apparent reason. Went back to the fitters - who plugged it in and diagnosed a faulty temperature sender, fitted an new one - no more dropping out. Hope this is useful.

Click to expand...

Thanks only problem is the fitter has since closed and I think he may have died. Wil take it to garage I now use for servicing the lpg system.

Kurgen: From the limited information I have on these things they all seem to have a diagnostic mode written in the software, the fitters originally had to turn mine off to allow me to manually turn the gas over until the new temp sensor arrived - it kept wanting to try to get the lpg running. If you can find somone who can 'talk' to your system ( apparently some fitters have more systems available than others), the diagnostics 'should' let you know what the problem is.

Sounds to me as if it runs ok with rev's but at idle it switches over to petrol, it quite possibly could be vacuum related.

You will have a vacuum sensor linked between the inlet manifold and your lpg vapouriser unit, basically it detects when you are running out of gas, and switches over to petrol.

check your vac pipes for leaks and ensure a tight fit, make sure the pipe has no oil inside it or the vac sensor.

If that is ok then on the side of the vaporising unit, (round aluminum unit also called a mixer) there is a adjuster screw in the center of the diaphragm housing, usually a 5mm hex wrench ( allen key) fitment, you should have a dual unit if the system has been fitted by someone who knows what they are doing, so there is on each side.

I suggest turning both in a half turn, this will increase the delivery pressure, which should be 1.3 bar at the fuel rail injectors.

Then take the car for a road test and see if there is a difference, if you have to turn more than 2 whole turns, and no improvement, return to the original position, and seek a reputable engineer who can inspect the system.

I have been running lpg for ten years on v8 discos, and fitted both my bigas sequential systems, its no different to a petrol set up, but the system and engine must be correct for everything to function, lpg is less forgiving than petrol, so i slight mis-fire on petrol becomes a dead cylinder on lpg, gas is weaker than petrol! you are injecting a liquid mist on petrol, which is compressed to a vapor (gas) for ignition, with lpg the engine is compressing a vapor which is expanding to a gas, therefore you have less substance than with petrol, so quantity in delivery has to be correct, and timing has to be correct.

Pat..