Starting on LPG from cold?

[camaro]

Is it bad for the engine or anything, or does it use loads of LPG? If I hold down the changeover switch on mine it'll start from cold no problem at all, just slightly longer cranking time. But if that's going to damage anything or massively increase my LPG usage, I'll just start it on petrol.
Incidentally, it wouldn't do this when it was at the installer's workshop - insisted on switching back to petrol until it reached 25 degrees!

[Speedy999]

What you're doing there is using the emergency start procedure. That's only meant to be used in the rare case that you run out of petrol.

The reducer needs to be warmed up to vapourise the gas properly. Best to let it run as it's designed to run, only takes a couple of minutes to warm.

[camaro]

No probs, I can do that - by the time I reach the end of my street it's warmed up enough that it switches over! But it does run perfectly from cold, on gas - I can't see it vapourising properly at freezing or below, obviously, but it doesn't seem to be having any adverse effects?

[Gilbertd]

If you start on gas from stone cold with the bonnet up and let the car idle, you'll see condensation and even possibly ice start to form on the outside of the vaporiser. As soon as it gets a bit of heat in it this will disappear. To vaporise the gas needs heat and it has to get that from somewhere and the more gas that is needed, the more heat it needs. If there isn't enough heat to stop the vaporiser freezing then you run the risk of liquid gas getting through the vaporiser and damaging the vaporiser and injectors.

[classicswede]

If you are starting lpg to remove the petrol wash then that is fine but some lpg injectors don't like to run cold. With the fact it does switch over quickly I would just let the ecu take control.

[LPGC]

Is Camaro's vehicle a Camaro or something else?

Also depends on the type of LPG system fitted.

Some single point setups will start on gas no problem.

It isn't usually a good idea to start a flat cold engine with a sequential LPG system on LPG:- Petrol is a liquid which needs to be evaporated into a gas before it will mix properly with air to form a combustible mixture. With a cold engine not all the petrol is evaporated, some liquid petrol can go straight out of the exhaust un-burned. Injected petrol that goes straight through the engine unburned doesn't contribute to the fuelling of the engine, so unburned petrol is equivalent to leaning the mixture. To compensate for this effect with a cold engine the petrol ECU will inject more petrol, this is the equivalent to pulling the choke out on an old carb engine'd vehicle. The choke effect isn't applied to actually create a rich mixture, it is applied to correct what would otherwise be a lean mixture given the 'lost' petrol that is unburned. LPG is a gas even at very cold temperatures so doesn't need this 'choke' effect to ensure the correct mixture with a cold engine. LPG has little chance of condensing into a liquid so is unlikely to go through the engine unburned. Any choke effect will have the actual effect of richening the mixture rather. Since sequential systems work as a slave to the petrol system they follow the petrol system and follow the petrol system fuelling strategy. This means that with a cold engine the mixture will be too rich if started on LPG.

People have already mentioned the potential for the reducer to get so cold that ice forms on it if a cold engine is started on LPG, obviously if ice forms on the reducer it's temp must be below 0degrees. When LPG turns from a liquid to a vapour it loses around 30 degrees in heat, so with a freezing reducer and freezing gas in the tank we could therefore expect reducer gas outlet temp to be at -30degrees... injectors won't like being fed with LPG at -30 degrees! Also, at -30 degrees LPG is approaching the temp at which it will turn back into a liquid, so the reducer may 'spit' liquid gas into the injector feed pipes instead of vapour, this both badly effecting the pressure in the feed pipes (as the liquid then expands in the pipes) and badly effecting injector metering (injectors get fed with liquid instead of vapour). On top of this, even if the reducer is above freezing and the LPG leaves the reducer as a gas, if it is still cold enough it can still revert to a liquid as it moves from a high pressure in the feed pipes / injectors to the lower pressure in the manifold...

Simon
Lpgc

[Gilbertd]

Is Camaro's vehicle a Camaro or something else? :lol:

Also depends on the type of LPG system fitted.

Some single point setups will start on gas no problem.

Nope, it's a Cherokee with a King system. See http://www.lpgforum.co.uk/viewtopic.php?f=28&t=13027

[LPGC]

Is Camaro's vehicle a Camaro or something else?

Also depends on the type of LPG system fitted.

Some single point setups will start on gas no problem.

Nope, it's a Cherokee with a King system. See http://www.lpgforum.co.uk/viewtopic.php?f=28&t=13027

It is possible, on certain vehicles fitted with AEB ECU's such as King that have reducer temp compensation, to adjust the reducer temp compensation to dial out the petrol cold start enrichment. Only achievable on the 'easy' undemanding conversions and mostly on older vehicles, and then probably not a good idea.

For a while I have wondered if any manufacturer will produce an ECU with OBD ability that will not only read fuel trims and show 'open loop' etc on screen, but when running open loop, such as during engine warm up, will have facility for a separate none slave (standalone) 'open loop mode' map.... This could allow for proper starting and running on LPG during engine warm up but only down to moderately low temperatures - probably all the time in summer and some of the time in winter. I am undecided on whether I think this will be a future development or not due to ECU emissions compliance testing etc.. But starting on gas has got to be better for emissions than starting on petrol and kicking unburned HC's out of the exhaust.

Simon
Lpgc

[marek]

Correctly fuelled, the engine will start just as quickly on lpg as it will on petrol. The only material difference is that there will be no unatomised (liquid) petrol collecting on the bores at startup. With a cold start on petrol, this unatomised fuel will wash the thin lubricating oil film from the cylinders and so increased engine wear would be expected when starting on petrol, relative to starting on lpg.

Once fired up, the water flow through the reducer has to be sufficient to vaporize the fuel from liquid lpg to gaseos lpg. This will vary from car to car as different engines will have a different volume of water in their cooling systems and the reducer may be plumbed in parallel to the ordinary flow out of the engine or in series (i.e. full flow of all water coming out of the engine). Essentially, the heat extracted from the water by the reducer(s) in turning liquid lpg to gas has to be exceeded by the heat produced by the engine's cooling system using the supply of water as conected.

In countries where sub-zero temperatures are common, it is possible to buy injector "heaters" to assist with cold starting and running in the first couple of minutes before the engine coolant has reached a sufficient temperature such that it is always able to supply the vaporization heat.

As almost all commercially available lpg sytems these days are piggy-back systems taking their settings from the petrol system they are attached to, they are generally not set up to work at these low coolant temperatures when the capacity of the system to supply heat to the vaporizer is uncertain. The performance of this type of bolt-on ECU becomes more predictable once all of the energy supplied to vaporize the liquid lpg is coming from the cooling system alone and this point on many engines is reached at about 25'C - hence the commercially available systems will usually be happy with a changeover temperature pitched at this level.

Your lpg usage ought not be increased materially by starting on lpg from cold. It will in fact be the period of highest cost savings when compared with petrol, due to the lack of petrol atomisation as explained earlier in the thread by Simon.

So long as the change from liquid to gaseous lpg is happening at the vaporizor, no damage ought to be caused.

kind regards
Marek

[camaro]

Muchos gracias to all for your detailed explanations.
Incidentally, it was a complete pig this morning to start on gas - despite it being warmer than usual, albeit much wetter - bucketing out of the heavens! Cranked and cranked for an absolute age before it eventually lumpily fired.
I would just have started on petrol, but my fuel pump/crash detection relay is knackered, so I'd have to jump out into the monsoon and put in a short jumper wire to get the petrol running - must fix that.
When I was originally up with the installer, he tried to programme it to start from cold but it wouldn't - but once it was home (and much colder) it would! Apparently some ECUs (PCM for a Jeep) learn after a few weeks, and mess about with things - so if it's still sulky going home from work then I'll back up his King map, reset the PCM (there's a procedure to do that), and see if anything changes.
Worst case, I'll have to fix that fuel pump relay sooner rather than later!

[Gilbertd]

Poor starting in the damp is usually down to dirty HT components, leads, dizzy cap and coil are favourite. What happens is that these things all get coated with a film of oily dirt which, once there is a lot of moisture about, allow the sparks to track down to ground long before they get to the plugs. I've seen it where you could see the sparks tracking from the nose of the ignition coil down to one of the LT connections. Give them all a good clean and the poor starting should go away.

A few years ago I knew someone who thought he had a car with a moral conscience. When he left his car at home overnight it would always start first time in the morning. If he stayed at his girlfriends overnight it would flatly refuse to start the next day. The difference was that at home it was garaged so didn't get the damp under the bonnet, at his girlfriends it was outside. All he had to do was polish the dirt of the top of the ignition coil and the problem was cured.

[LPGC]

Muchos gracias to all for your detailed explanations.
Incidentally, it was a complete pig this morning to start on gas - despite it being warmer than usual, albeit much wetter - bucketing out of the heavens! Cranked and cranked for an absolute age before it eventually lumpily fired.
I would just have started on petrol, but my fuel pump/crash detection relay is knackered, so I'd have to jump out into the monsoon and put in a short jumper wire to get the petrol running - must fix that.
When I was originally up with the installer, he tried to programme it to start from cold but it wouldn't - but once it was home (and much colder) it would! Apparently some ECUs (PCM for a Jeep) learn after a few weeks, and mess about with things - so if it's still sulky going home from work then I'll back up his King map, reset the PCM (there's a procedure to do that), and see if anything changes.
Worst case, I'll have to fix that fuel pump relay sooner rather than later!

If you try to start on gas and the engine won't fire up, it's best not to keep cranking too long.. There is the potential to fill the exhaust with a very explosive mixture of gas and air, then as soon as the engine fires that explosive mixture gets lit and the exhaust can be blown apart. I only forgot this once ever! Owned a Talbot motorhome and, of course, converted it to LPG. The coolant was very dirty so I kept flushing the cooling the system, running the engine and flushing again. I wet the electronic ignition and the engine wouldn't start, so aware of this I thought it better to try starting on gas instead of petrol to prevent flooding the engine. Bang, deafened for a while and both exhaust boxes blown wide open! Would fix the fuel pump asap!

Simon
Lpgc

[camaro]

Cheers all - I have a new set of plugs, HT leads, dizzy cap and rotor arm to be put on - I mean, I've only had them for about 6 months so it's not like I've had a chance...
Didn't get to start it on gas today - managed to flatten the battery by leaving an interior light on overnight! Handily a Taxi stopped (at 5 in the morning!) and gave me a jump start, I have the world's beefiest jump leads - so put in the fuel pump relay jumper and fired on petrol like they want you to, then let it switch to gas by itself. Worked grand, the only bugger is that I have to remember to take the jumper out when I get to where I'm going, or it'll be another flat battery!

[DodgeRover]

I've had a couple of cars that have been gas only when the petrol side of things has given up, have only had problems in minus temperatures at high altitude - just gave them a quick sniff of easy start and away they went, no issues (that i noticed) with the vapouriser icing up once started. I was on much much older tech than you though but is there a prime setting in your system - used to give a short amount of gas before you started cranking?

[camaro]

Not that I know of, it does take a couple of extra cranks to fire on gas from cold so I presume the "emergency" cold gas start just forces the gas system to start straight away. It's not even mapped that low as far as I know - it's a 25 degree changeover. I'll know more once my lead arrives and I can download the map!