Prado on LPG Not Starting

tryagain on 17/03/2018 - 20:36
Last edited 18/03/2018 - 05:27 by 1 other user

Looking for someone who has a bit of experience with car LPG systems. Our car isn't starting or running on LPG after filling up the tank.

It has done this a few times in the past and we found it was happening when we filled up from a certain service station so stopped using it. Recently it has been happening a lot more, even after filling up from our normal service station. Just to clarify after filling up it doesn't want to start or run on LPG, after a few tries over a few days it will usually start (when the engine is cold in the morning is usually when it happens).

Once the initial start has happened on the full tank it will then start and run normally for the rest of the tank. I was planning on not filling the tank right up to see if it made a difference but haven't been able to get it to start on gas for the last few weeks.

I could take it into someone but as the tank is near expiry. I only plan on keeping the car for another 1-2yrs, and gas isn't as cheap as it once was. I haven't decided if I think it is worth potentially paying someone to fix it as well as getting the tank checked or if I just swap it back to all petrol by myself for the next 1-2yrs (car isn't worth that much)

Any help would be much appreciated.

edit. It is fine on petrol.

Automotive

Comments

  • Stewardo on 17/03/2018 - 20:46
    +1

    Sounds like it needs a service, if you can find an old taxi driver hanging around the taxi rank during the day, they might advise you of a cheap lpg repairer in your area, a lot of the old taxis were lpg.
    I had an old falcon like that, it was dual fuel. It was temperamental to get it going.

    • tryagain on 17/03/2018 - 20:53

      Thanks, For a service they just generally give it a tune, but it runs fine when the tank isn't full, it just an intermittent issue only when the tank is full.

  • thetrain on 17/03/2018 - 21:17
    +1

    What model/make? Is it a Falcon?

    Sounds like a stuck solenoid from wax in the gas. The solenoid is like a switch to let gas through when the car is on, so if it is a bit sticky it can require some driving (bumping) to get it unstuck. IF it is a sticky solenoid a quick clean will make it work like new.

    • tryagain on 17/03/2018 - 22:53

      Thanks, it's a 90 series Prado, the two solenoids in under the bonnet seem to be clicking away fine when tested, the one on the tank is hard to get to so not sure if that could be the issue

      The fact that it only happens when the tank has been filled but is otherwise fine makes me think that it might not be a sticky solenoid though.

      • thetrain on 17/03/2018 - 23:36
        +1

        Cool, I don't have much experience with Prados (or aftermarket conversions). Injected or mixer style?

        If it is mixer it should be relatively easy to diagnose

        • tryagain on 18/03/2018 - 07:08

          Mixer type.

  • effgee on 17/03/2018 - 21:19
    +1

    What happens if you start and run on petrol, then change across to LPG once the engine/engine bay is fully warmed up ? I'd try this, then you can use some of the gas and see if it starts ok with a less-full tank of lpg.

    Have you checked your cooling system ? Lack of water in the cooling system (radiator) means lack of heat to the 'gas converter' which has the job of boiling the liquid lpg into a gas so it mixes with air to start/run your engine. Along the same lines, even partially blocked coolant lines going to the converter, or internal blockage in the converter could explain the failure to run. You could also have an 'air lock' in the cooling lines, reducing water flow without actually being blocked (solution there is to bleed the air out). I'm assuming you've got an older 'carburettor' style system, not an liquid injection system.

    Another possibility is a blocked filter, typically on the inlet to the regulator. I was told once that tank manufacturers has a 'trick' of putting newspaper in the tank and burning it to use up all the oxygen in the tank (cheap-arsed way of creating an inert atmosphere) before final welding, but the leftover ash had a habit of clogging filter-regs. Should be relatively cheap to replace, but needs some expertise (you'd need to isolate the tank, bleed off any lpg in the lines and converter which can be dangerous if done without care, (safest way would be to run the engine on lpg until it stalls) replace the filter then leak check the connections afterwards).

    Another factor is the ratio of butane/propane varies between suppliers, which lines up with the servo you now avoid. Butane takes more energy to convert from liquid to gas, and when the engine is cold there's very little heat available in the coolant to evaporate the liquid, but the fuel demand is high due to the cold start needing to be rich.

  • tryagain on 17/03/2018 - 22:59
    +1

    Thanks, it won't flick over to gas, just cuts straight out. I don't think it's the converter freezing up, as its quite hot to touch after its been running on petrol for a bit. The filter is a possibility, although I don't know why it would be causing the issue when the tank is full but not otherwise, again same with the ratio of the gas.

  • Euphemistic on 18/03/2018 - 05:57
    +1

    Don’t fill the tank all the way up? Possibly easier said than done.

    It sounds like some sort of over pressure or overfill problem, but I know little about lpg systems. I’m aware the tank is only supposed to fill to 80%, but if yours is somehow going a bit over that there might be a sensor or something playing up.

  • doctordv8 on 18/03/2018 - 11:07
    +2

    You need to take it in for back to basics testing. Let the Qualified LPG experts deal with it as it is Licensed Trade and for good reason. LPG explosions kill if not installed, repaired and or maintained correctly. It is as an automotive alternative fuel when fitted to comply with AS it is exceptionally safe and with many built in redundancies.

    Google this. LPG expands x? to a vapour, and then expands x? on ignition. You will scare yourself. Do not play with it.

    Safety message over. Based on near 30 years experience, and your description: Toyotas/Prados were/are a good conversion brand, reliable and if installed with quality bits lasted well into the 2nd tank life, post 10yrs.

    You - unqualified - can NOT touch and disable/remove the LPG system, legally and for safety reason stated above.

    A diagnosis is also dependent on a physical inspection, but you also leave out so many details and facts on the vehicle, conversion and symptoms.

    It can be bad gas, but that is the least most unlikely scenario. Bad gas is bad gas, and it will either not start - at all - difficult to start and or very poor performance. Every time. Until that fuel load is gone, it will remain bad gas.

    Regardless of fill level, it will run if all other systems are ok. It will slowly loose power when nearing empty, and will not have any effect of starting whether 10%, max legal 80% or modified(tampered with 100% - illegal/dangerous.

    A diagnostic service will solve the issue, as until it starts and runs it can not be 'serviced', hence the service will be a repair first and then servicing to finish it off. Give them a running vehicle, they can refuel it and carry out diagnostics as they see fit during the process of the fault developing. At the point of non start, it is either gas flow or engine condition, which is so easy to test….even in our sleep.

    Pending the system installed, there are up to 4 solenoids, and the click is one good test measure, but not an absolute, as the valve/s controlled by said solenoids has orifices - which can be damaged, blocked, or not operating fully/correctly. 2 parts - the electrical solenoid that moves a mechanical valve. Liquid flow still needs to be confirmed thru a valve and or the system component it controls.
    Direct Injection or Vapour Mixer style it makes no difference mechanically, although the Injection system will also require computer diagnostics as well.
    A coincidence involving valves and refueling times are a possibility for not starting.

    Getting an idea why asking such open ended questions are a nightmare…..just take it to a LPG tech, which reminds me…
    How long is a piece of string?

    It will not be…Converter/water heating. As correctly stated,(Liquid withdrawal system) gas converters require hot engine coolant to stop the Convertor from freezing due the the reaction - LPG changing state to a vapour under load. If it runs, it runs. Turning a functioning LPG vehicle off at the servo and failing to restart 5 minutes later is not due to heat conversion loss. Even without any heat starting from dead cold, an LPG engine will start and run for a good while until a heavy load gas draw causes a freeze.
    So, this has nothing to do with refueling and not starting.

    LPG Tanks are high carbon steel and cold rolled during manufacture and this releases a fine carbon dust, which is a blocking beast for the fine paper filters in the engine bay gas lock, but as this is cleaned/replaced during the first service, it then should never become an issue. Dirty gas is the next filter blocking beastie and again, simple filter cleans/changes during normal system servicing resolves this and any possible cause for concern. Besides, a blocked filter partially or badly will only cause a loss of full power under load, and until roughly 90% blocked the engine will still start and run as it requires the least amount of fuel - exactly the same as petrol.Oh, you can not over pressurize the tank on refueling either.
    So, this has nothing to do with refueling and not starting.

    Fuel quality is a performance issue, but with modern testing and quantitative regulations giving us the minimum preferred 60/40 mix at the bowser, and again, the difference is high load performance and economy. So unless it is exceptionally bad fuel…. this has nothing to do with refueling and not starting.

    But….a build up of Tar from lower quality fuels over an extended period of time can gum up valves, vapour control components and hoses. So this can have something to do with refueling and not starting if only by coincidence.
    Your a smart guy? and so regular servicing will remove this as a possible cause/issue.
    So, this has nothing to do with refueling and not starting.

    Questions. Battery/wiring/earthing: poor/low voltages on hot or cold high draw cranking can leave solenoids and controls inoperative in some circumstances - so battery condition?
    Do you let it run out of gas completely or just refuel at random when getting low?
    Do you refuel during hot of the day or cold of the night?
    Did this make any difference?

    I can not/will not not say what the fault is, intermittent ones are the worst but you need to have it seen by qualified techs. Regarding the tank life and testing costs, + keeping the old girl a year or two more, half price fuel will be worth it if you do the k's. If not removing will cost you, and then you also loose the added value on resale.

    Get it seen, quoted and then make a decision. Now you have some info to chew on to make the choice to get it seen to easier I hope.

    • tryagain on 18/03/2018 - 13:26

      Thanks for taking the time to reply, and the safety warning, when I say remove it and return it to rust petrol, I would get it decommissioned first at a gas place before doing it, I have no desire to work with high-pressure gas.
      Part of the reason I am trying to figure out what might be causing the issue is to avoid the "it took us a day and a half to diagnose it and we ended up having to replace everything (because we didn't really know what we are doing) so here is a bill for 2.5k" I have also found knowing what the likely issue is beforehand, helps to give the mechanic a head start, let's them know you know what is happening so you don't get "extra repairs" added on, or you can go in playing dumb to start with and see how knowledgble/honest they actually are. If it was a simple get them to give a quote I'd do that but I know unknown intermittent faults seldom work that way. To answer a few of your questions.

      I don't think it is a voltage issue, the times it has started after not initially have mostly been after it has sat for a while so the surface charge would have drained off and if low voltage was an issue, it would be less likely to start then than more.

      We generally let it start to run out of gas (km travelled + a slight loss of power is usually the trigger to swap it over to petrol, I have had a few people raise an eyebrow at doing this but so far after about 10yrs and about 250k km it so far hasn't seemed to cause any issues.

      Have refilled in heat of the day and at night but not enough times to be able to be able to know if the temperature at fill time is a factor or not (exhaust runs next to the tank so enough heat would get through the heat shield to further muddy the waters with this one). The times it has started after not have predominantly been when it's cooler and the car has been sitting for a while so the Gas expanding and cooling is a decent probability of contributing to the issue in my mind.

      The spark plugs are probably due to be replaced so that might be contributing to the problem, but couldn't see that being the issue in isolation, but the more I think about it the more I am inclined to think it might be a combination of factors as opposed to just one issue.

  • tryagain on 18/03/2018 - 23:54

    Think I have come up with the probable issue that makes sense of everything, I think the excess flow valve on the tank has tripped, I think if we let it run out of LPG before we fill it, and then after filling it the pressure in the tank being full builds to a point that then trips the valve when it tries to repressurise the pipes between the tank and the converter. The intermittent part is that it only happens when it is filled with cool gas that then expands a little with the heat, would make sense as to why it starts in the morning (after not starting) as it would have cooled/contracted somewhat overnight. The service station that caused the issue the most I just went and had a look at and it has an underground LPG tank so that would be fairly cool going in which would explain why that one was worse, also the repeated attempts trying to start it over a few days would likely let a little gas out each time to just drop it below the threshold where it cuts out. I will try resetting the valve and only turn it on a 1/4 turn to see if I can get it to slowly pressurise the line.

    • blackwoodshadow on 02/01/2022 - 23:38

      i just joined the site to say thankyou for posting your theories and experience on your problem. I travelled from Khancoban to Melbourne today [hot one] and had to do the whole trip on petrol because of a similar presenting issue as yours in the op. I have a 2.7 2wd hilux with rebate LPG system nearing 10 years old. This is a bit of a story but there is some relevant stuff in here somewhere.

      I usually start it on petrol and swap over to gas after she warms up, mostly to run some lube through the head as i don't have a dripper or anything. Last 6 months or so I have exclusively started it on petrol because the cranking time to ignition on lpg has got longer and longer. This has got me thinking about solenoid filter/vaporiser gummed up/whatever but it hasn't been a real problem because we have been locked down within 5kms of house for so long I haven't had that naked feeling of one fuel not working too well/at all.

      I have troubleshot the cranking time a little bit by testing if solenoid behaves differently when switching compared to starting on lpg etc but there has been no real consistency or control in my casual approach and I have been pretty blase about it tbh with the last 2 years of background noise. I am not trained but I have been working on cars for 30 years and I enjoy the process of investigating and solving problems. Did I say enjoy- except for intermittent issues although they are the most satisfying to solve they are a pain in the posterior. However I know stuff all about LPG, esp. the failsafes in the system so it is harder to pinpoint likely sources of issues, for me, than if its not running on petrol.

      So, to get on with it. I had about 80 kms left in the lpg tank when i left Khancoban but there is no LPG up there and I knew I would need to switch en route- something I felt could be dicey as the road to Wodonga has a lot of holiday traffic and there are always idiots, I didn't want to risk losing accel/response if someone with suicidal tendencies decided to overtake on a blind crest etc just as the gas ran out/got close. So I went on petrol.

      I pulled into the servo at Wodonga and screwed on the lpg nozzle and nothing happened when i squeezed. I undid it and tried again and she started filling. Dodgy nozzle, happening more and more I find. Anyway it was pretty hot as I said. I have a bad back so I put the trigger lock [don't usually do this] on and stretched my legs and back a bit, a spot of deep thought. After a little while I thought hmm what's happening, there was no usual noises and flow cutoff as the tank filled to max, instead the gas was stopping, then going in for a few seconds, then stopping in a cycle. I released the lock but when the trigger returned to rest there was no PSSSHHH purge. I thought am i gonna die but managed to control myself and squeezed and released the trigger and thank the lord i got my PSSHHH.

      I came back from paying and started her up on lpg- usually when the tank is full the cranking time is much less- and… nothing. Switched back to petrol, started up and switched to lpg- this sometimes makes the solenoid click louder for want of a better word- and… nothing. So I drove out on petrol and tried switching at a few revs, nup.
      Hmmmm. Pulled over and undid the earth, reattached, seemed clean and tight, checked fuses, switched it with hand on solenoid feeling for action blah blah, thought hmmm it must be the solenoid i guess?, maybe its clogged up, maybe it just carked it, i dunno its hot, i need to get home, will fix it later, off i go.

      Which brings me to finding this thread tonight while looking at solenoids and filters online and parallel doing some poking around. And this last post in particular got me thinking about the dodgy nozzle not shutting off, hot day and possible pressure/flow sensor and I went outside [its 16 degrees cooler now] and switched her over to lpg after she started on petrol and gas is flowing like usual.

      Which is not to say I understand why, or all the issues are resolved, I still need to sort out the reluctant starting [it now occurs to me i might have a leak yikes] but it is reminding me that sometimes there are multiple unrelated or at least not mutually inclusive things going on, so thankyou to all contributors, especially tryagain for freeing up my thinking and adding to the soft library of weird things that might not occur to you at first but someone else has written about it in the spirit of sharing information for those that come after.

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