lpg kinda misfiring

[mateusz]

hello gentlemen ive got issues with with one rangie i own. it kinda missfires as i drive down the highway continually more so under load.
Ive checked hoses from mixer to air boxes all seems well. today i got 22litres per 100klm consumption. believe it or not it seems a little low! The vehicle is hard to start especially in cold mornings. Technique to start engine hot or cold is lpg switch on neutral position then when the vehicle fires i switch it onto gas! Can this mean at idle the mixture is too rich and possibly mixture at load/highway speed has become a tad lean? can i check the spark plugs for evidence of this? thanks for reading i hope i can get a few ideas. i havet changed distributor cap and rotor....otherwise spark plugs were new 3 months ago as well as the leads. im thinking its a fuel issue tune up required. the screw that allows max flow into air box i think is abount half way...

[langy]

In reverse order, make sure the flow adjuster ( that screw that is at halfway) is at the right position. It's like a little airfoil, and if in the wrong position can strangle the mix ( Is it 180 degrees out?). Otherwise, make sure all the connections upstream of the intake are tight so you get all the vacuum you can. Small leaks on the gas hose after the converter can make starting hard. Re check the gaps on the plugs. Last, make sure all the plenum vacuum connections are ok or sealed. They are the likely suspects.

[bee utey]

It sounds like your lpg converter is leaking gas into the intake, flooding it on startup. Either that or its an EFI vehicle and it starts with the help of a bit of petrol.

Your lpg mixture adjustments, petrol overlap, spark plug heat range, plug gap, ignition idle and advance timing, ignition amplifier, ignition leads, and basic setup may all be at fault to some degree.

How about some details of what vehicle the gas is on, what engine, what gas system, and tune up specs? Pictures?

[geodon]

I've developed a high speed misfire under load with LPG. Idle & low speed are fine. It's a very basic Impco system.

Goes on petrol with no problems.

Petrol supply is easy to investigate but how does one check LPG supply without self-immolating?


**OOOPS! Sorry I meant to start a new thread.**

[bee utey]

I've developed a high speed misfire under load with LPG. Idle & low speed are fine. It's a very basic Impco system.

Goes on petrol with no problems.

Petrol supply is easy to investigate but how does one check LPG supply without self-immolating?


**OOOPS! Sorry I meant to start a new thread.**

Leaning out the gas due to supply issues shouldn't result in misfiring, more likely a total power loss.

As for the gas supply, I strongly suggest you take it to a gas fitter and ask him to do the work. He will know which filters may need a clean out. Otherwise turn off the gas tap at the tank, run the engine until it stops, dismantle and clean. Check thorougly for leaks before you drive too far.

[mateusz]

The lpg system ive got is the AT90E Model. Plugs and leads within 5 months old? could the gaps make such a difference? What gap do people recommend. To check for leaks do i use soapy water? The weird thing is sometimes the car goes great, sometimes it begins to stutter???? maybe one of the leads are loose on the dizzy or spark plug. Just out of curiosity what happens when diaphragm rips? is it total power loss?

[bee utey]

The lpg system ive got is the AT90E Model. Plugs and leads within 5 months old? could the gaps make such a difference? What gap do people recommend. To check for leaks do i use soapy water? The weird thing is sometimes the car goes great, sometimes it begins to stutter???? maybe one of the leads are loose on the dizzy or spark plug. Just out of curiosity what happens when diaphragm rips? is it total power loss?

The right plugs are much more critical than most people realise. Regardless of brand name, they should be at least 1 heat range colder than standard, and a gap of 0.7mm to 0.8mm, the smaller being better in this case. Out of the box many plugs are 1.1mm gap which raises the voltage to fire the plug by 30-40%. Now tell me that doesn't have a bearing on misfires. And in 5 months your plugs will have rounded electrodes, which also adds to the misery of a poorly chosen plug. Your plugs sound like they are on the edge of coping.

For personal preference I use Bosch WR7DC+ spark plugs, gapped to 0.7mm/0.028"

The effect of a diaphragm rip will depend utterly on the size of the rip. A 10mm rip will cause major leaning out and the engine will hardly run. Have someone check your converter or pull the back off and look yourself. Take care to not tear the diaphragm, they are usually very thin for good sensitivity.

BTW the AT90E is just a description of the lpg converter type, not what the system is. Very few gas "systems" use parts from only one manufacturer. Most use a range of compatible parts where sometimes they are "badge engineered" by the wholesalers to make them look consistent. Parnell used to be good at that.