2000 3.5 TH done 180k, I had it converted to lpg 4 years ago.

Has 3 issues:

1) LPG: Last winter on really cold mornings (< 10c) starts fine on lpg, drive off and 50 metres down the road come to intersection and stop and stalls. Will not restart on gas, flick to petrol and starts, flick back to gas and no further problems. Does this almost 100% of the time on cold mornings. No problem at the moment (summer). Prior to last winter would be fine starting on lpg on cold mornings. No problem when cold on petrol.

2) LPG: When engine has completely warmed up ie after 30 minutes of decent running. Switch off engine, wait 10~30 minutes, restart engine and revs go to 1500 or so for a second and slowly comes down to normal idle speed then runs rough/misses and stalls (takes about 5~10 seconds to stall). Will not restart on gas, does not appear to even fire. Switch to petrol and starts, flick back to gas and continues to run. Happens 70% of the time given above circumstances.

3) Petrol: When engine has completely warmed up ie after 30 minutes of decent running. Switch off engine, wait 10~30 minutes, restart engine and starts ok. Put into drive and put foot on throttle. revs will not go above 1500, misses/coughs really bad. If put foot flat to boards eventually leaps into life after 10 seconds giving driver bad case of whiplash. Runs fine after that, does not do this on lpg. Happens 70% of the time given above circumstances.

Have replaced O2 sensor (stuffed), had injectors removed and ultrasonically cleaned, new air and fuel filters, new plugs all round. Inspected dist cap and rotor these look ok. Removed isc and cleaned, wasn't real dirty anyway. Checked tps and maf sensor according to ws manual and appear ok. PCV valve appears ok, replaced other breather hose as rock hard and cracked.

No fault codes.

Have had it to lpg installer who picked up o2 sensor and replaced but didn't change anything. Had it to my mechanic but everytime they have it it works perfectly! They did recommend injector clean which has made it run a bit smoother but not cured above problems.

Did 10l/100km on recent country trip on lpg.

Not sure what to do/check next, any ideas welcome or if anyone knows really good lpg servicer in Adelaide.

Check the safety cut-off valve. Had a very similar problem to this with my Magna. This was replaced and cured a misfire and starting problems. Last year I had almost the same symptoms you describe. Tried a couple of local "experts" and they couldn't find anything. I took it to Silver Repair service in Kensington, Melbourne (they are the best for LPG diagnosis I have found). They found that the secondary safety cut-out switch, which was hidden under the dash near the LPG/Petrol switch had a loose connection, this was causing problems when the car started to warm-up and cool down, I guess it was just expansion of the electrical connection.

Items 2) and 3) perhaps confirm the changeover switch scenario. You will have residual gas or petrol on changeover and if the safety valve isn't closing properly, you'll get a too rich mixture until the excess has burnt off.

Is the secondary safety cut-out switch just another simple electrical switch rather than a gas solenoid/valve?

Is the secondary safety cut-out switch just another simple electrical switch rather than a gas solenoid/valve?

I think it's an electrical switch, not a simple on/off but perhaps a relay that operates when the gas pressure is detected. There seems to be a delay when I turn on the ignition and I can hear the relay click and the lights on the LPG/Petrol switch don't come on until I hear the click.

I was always told to warm the car on petrol and never start it on gas. I think its the gas doesn't completley combust and I believe it may cause damage?

Warm it up for 5 mins on petrol then switch.

Regarding No 1, your gas converter could be leaking a bit and emptying. When the gas goes through, it causes massive temperature drop and the converter could freeze. After a while, particularly running on petrol, the converter will have enough hot water in it to overcome this. When it stalls, check to see if there is ice on the outside of the converter. If may give some indication of what is going on inside.

Regarding No 2. as Waynenev says above, maybe your gas system is not totally isolating the gas supply, and you are getting some leakage of gas through the converter. Too much and it will not start because it will be too rich. When the extra gas has been used up, idle will return to normal.

Regarding No 3, maybe the gas leaking could cause this as well because it will be too rich on gas and petrol. Once you clear the excess gas from the system, it will run OK.

There should be 2 solenoids in the gas system - one at the converter and one at the gas tank. Both should seal, but maybe they don't. Quite often, installers take out the solenoid slug from one of the valves because the losses as the gas passes through when cold may cause starting problems. You can check if they are working by simply pulling the power from the solenoid as the beast is running on gas and see if it stops. It should.

Incidentally, you are getting good economy from your car.

There should be 2 solenoids in the gas system - one at the converter and one at the gas tank. Both should seal, but maybe they don't. Quite often, installers take out the solenoid slug from one of the valves because the losses as the gas passes through when cold may cause starting problems. You can check if they are working by simply pulling the power from the solenoid as the beast is running on gas and see if it stops. It should.

Ok,

I tested them by disconnecting power when running on gas and engine stopped, so doesn't appear to be causing the issue.

I thought I'd bump this with an update. Took it to a gas specialist place and they checked it out, said the gas mixture was really lean. They adjusted the mixtures and also reterminated all the spade connectors on the gas equipment. This has now fixed the stalling when warm issue on gas. I won't really know whether its fixed the cold stalling gas issue until we get some cold mornings here in Adelaide.

My running rough when warm on petrol still exists (ie 3 from my op). There must be something happening in the 1st 30 seconds or so when the engine is warm that causes this. At all other times the engine runs perfectly. I did end up putting a new dist cap & rotor in just in case as they ones in the car were the original ones but this has made no difference.

Not really sure where to go from here.

You may still have some issues with a bit of residual gas in the converter when you switch to petrol - it will run too rich until the gas is burnt off. If you have a 3 way switch (LPG/Neutral/Petrol), go to the middle position on changeover and see how long it takes for the engine to die.

You may still have some issues with a bit of residual gas in the converter when you switch to petrol - it will run too rich until the gas is burnt off. If you have a 3 way switch (LPG/Neutral/Petrol), go to the middle position on changeover and see how long it takes for the engine to die.

It is fine when you switch fuels.

I dont have a 3 way switch but I did test the cutoff valves by having the engine idle on gas and then I cut the power to each of them in turn, the engine cut out instantly. I also got the gas guy to test them and he said they were fine and not leaking.

The issue is when you are running on petrol only, stop the engine and then restart it after a time.

OK - if it is petrol only giving the problem, maybe you have an injector (or more?) leaking. This makes at least 1 cylinder too rich & either totally mis-firing, or at least too rich to run properly. When it finally clears its throat, it will run OK.

Do you use petrol regularly? I didn't (I am a tight arse and didn't want to use expensive petroil when gas was available). Eventually it wouldn't run cleanly on petrol and I had to get the injectors cleaned. Having solved that particular problem, I finally sold the car and it still runs well. What a difference! Maybe this is what you need to do as well? (Clean the injectors, not sell the car).

6 months ago I had the injectors cleaned...it was done on a changeover basis.

It was doing it before they were changed over and it still does it after.

It runs ok when it initially is started...idles fine, its after you put it in drive and put your foot down that it starts to miss.

And I usually run 15~20 litres of petrol through it a week.

The automated system in my magna always starts on petrol, and flicks to gas once the water temp is above 28 degrees. That's when the needle on the temp gauge is at the second mark (consistently).
if you run gas to early, the gas in the liquid state freezes as it turns into a gas, ( latent heat or something) it needs the warmer water running through the converter to prevent freezing the system/nozzle blocking partially or completely.
Takes about 2-3 minutes in summer and 6-7 minutes in winter, I use more petrol in winter :(, our winters are a lots less severe than yours, I'd imagine.

The automated system in my magna always starts on petrol, and flicks to gas once the water temp is above 28 degrees. That's when the needle on the temp gauge is at the second mark (consistently).
if you run gas to early, the gas in the liquid state freezes as it turns into a gas, ( latent heat or something) it needs the warmer water running through the converter to prevent freezing the system/nozzle blocking partially or completely.
Takes about 2-3 minutes in summer and 6-7 minutes in winter, I use more petrol in winter :(, our winters are a lots less severe than yours, I'd imagine.

Mine's manual, it uses a Gatec processor http://www.gore-research.com.au/pdf-files/fp32-instructions-2nd-edition.pdf

This morning it was 10c and it started fine, so the cold start issue may have been fixed. Its just the petrol issue which is driving me crazy!

It still sounds as if there is too much fuel in the intake manifold - either petrol or a bit of gas thrown in for geood measure. After a short time, this extra fuel is sucked into the engine and either burnt or thrown out the exhaust and then it runs fine. If you get someone to start the beast and you wait at the rear of the car and sniff the exhaust, you may pick up something. If it is excessively rich, you will smell either gas or petrol, but only if it is really rich. I had my Pajero once suck in a part of the intake resonators (those bulbous lumps on the side of the intake before the air cleaner). This caused it to rub ultra rich and there was unburnt gas coming out the exhaust. It smelled really bad. Eventually a local gas bloke found the problem, but only after he had fitted a new converter. Yours probably would not be as bad as that, but you may be able to smell either gas or petorl. That may give you a clue as to which system to chase.

Just because you had change-over injectors doesn't mean that they are perfect. I would rather have my own injectors/heads or whatever back because at least I know the history of that particular component. I hope that you can fins the problem soon....