Lpg takes ages to switch over from petrol

[patnut]

It's been like this for a while sometimes on short trips not switching over at all dispite sufficient engine temp.

Is there a manual overide or can I change the settings in software to ignore engine temp and switch over after a certain time?

Thanks
Pat

[Brian_H]

Switchover threshold is adjustable - first point of call is to check how hot the vapouriser is getting (if its only getting some coolant flow it can take a while to get hot - in which case address that). It could also take a while to reach the switchover temp, some ecus can be set to not switch over for a couple of minutes if started on a cold engine. An airlocked vapouriser will take ages to warm up as well.

If its getting hot, is this reflected by the temperature sensor in the software? Some of them are inline on a hose, and glued into place, its possible for the sensor to come away from its housing in this case without any leakage, that may account for it. Or the sensor may be misreading as its worn out or badly connected?

Really first port of call is have a look in the software and go from there if you have it.

[patnut]

Thanks Brian_H,

I have the software and will check. I think it could be an airlocked vapouriser as I remember the installers saying to me that there is an air pocket in the cooling system (which I thought they had fixed) Is this the same thing?

Also is there a way of forcing the system to switch to LPG. I thought by holding in the lpg switch button and starting the engine that would do it but it doesn't. It's a stag system.

Thanks

[Brian_H]

Yes an air pocket is the same thing - you may find particularly if the unit is quite high up in the engine bay that its prone to doing it when the coolant is disturbed, or if there is a leak. Not sure on the force to start on gas as I've not seen stag, but it does exist on some systems. but you really want to check the vapouriser is getting hot first, as if it isn't you might cause problems with that in trying to force it to start from cold without a decent flow through it.

Have you had to top up coolant? If so, you might find its as simple as loosening a hose clip on the vapouriser and letting any trapped air out of it (stick the hose back on once coolant starts to flow out). It would suggest you have a leak somewhere though as well if so.

[patnut]

Sorted! It was a coolant leak so coolant level was low.

[Budgetbond]

Incidentally assume a fully operating good cooling system and hot vaporizer, what are the minimum threshold values time and temperature you can use to ensure the quickest efficient switchovers?

[Brian_H]

Depends on the car, mine are set to 30 degrees, but it can depend on the cars cold start behaviour as to what time is needed, if it even needs to be set.

[Budgetbond]

What about time Brian, any general idea of the minimum time from cold you can set them too?

[Brian_H]

As far as I know it depends on the car, some will come off cold start enrichment quicker than others. I don't think any of mine have a delay set on time, just temperature set

[Gilbertd]

Some systems, like the eGas I had on one car, have a time but that doesn't enter into it on a cold start. On a cold start it would switch over when it reached the temperature but on a hot start it used the time. So rather than starting on petrol and immediately switching over as it was already up to temperature, it delayed switch over for however long the time was set for. As I didn't have a proper cable for it and the software was as reliable as a chocolate teapot, I wasn't able to change it to whatever was the minimum. A real pain to be running on LPG, stopping to fill up and then having it run on petrol for a minute before switching back over again.

[Budgetbond]

Yeah sorry good thinking both values have to be met don't they so it's only really temp that matters think I put it down to 28c initially I suppose time could be set to the bare min then for a quick kick in. (I do mainly round town driving),
Cheers

[LPGC]

The minimum temperature for changeover can depend on lots of aspects.
The engine running with choke effect has already been mentioned.
The type of reducer, it's pressure setting, type of injectors and available ECU settings can all play a part. For some installs the driver's behaviour can also play a part.

Some ECU's are capable of pre-warming injectors, most are not. Some ECU's can be set up to switch to gas at relatively low temperatures but temporarily switch back to petrol if the driver puts his foot down while the engine is still relatively cool and gas and/or reducer temperature fall below a certain level, most cannot (this feature can allow setting relatively cool changeover temp without causing problems if the driver puts his foot down while the reducer is still at maybe only 30C). When these 2 features are available 'drivers behaviour' becomes far less important.

Some ECU's temperature correction works better than others. Some reducer/vapour sensors are more accurate (or more quickly reflect changing temperatures). Some ECU's are capable of limiting peak injector duration during relatively cool engine conditions, some cannot (can be handy on e.g. VW stuff that sometimes apply choke effect during heavy loads while the engine is still warming up even though for lower loads the engine runs closed loop normal mixture). On relevant vehicles an ECU's ability to limit peak ginj can mean driver's behaviour becomes less important.

Some injectors don't work too well with cold gas, especially at higher pressures, they might not open at all under such conditions unless pre-warmed.
Some reducers are much better at transferring heat from their body/water to gas than others. Some reducers are prone to outputting pressure that is quite a bit higher when the reducer is cold than when warm.

With some ECU's and components, especially on certain vehicles, especially for some drivers, changeover temp can be made much lower than with other ECUs.

I make sure installs I fit change over at relatively low temperatures but perform properly at low temperatures and that any sort of driving couldn't trip them up at any temperature.

[Budgetbond]

Yeah switching over quickly whilst mainly urban driving is useful, I've reduced the switchover to 20C and it kicks in slightly quicker and efficiently (I mite try and reduce this further now it's Spring) but it's still 3/4 to a mile before it goes onto gas.
I've tried to make my coolant system and reducer(+log) hoses fairly efficient, but I suppose it might just be my car. (Poss slightly sticky thermostat)
Maybe I'll try completely turning off my heater settings to cold next time as mine isn't plumbed into the heater hoses to see if that makes any diff come to think of it)

[Brian_H]

Yeah switching over quickly whilst mainly urban driving is useful, I've reduced the switchover to 20C and it kicks in slightly quicker and efficiently (I mite try and reduce this further now it's Spring) but it's still 3/4 to a mile before it goes onto gas.
I've tried to make my coolant system and reducer(+log) hoses fairly efficient, but I suppose it might just be my car. (Poss slightly sticky thermostat)
Maybe I'll try completely turning off my heater settings to cold next time as mine isn't plumbed into the heater hoses to see if that makes any diff come to think of it)

Where do you have it plumbed into if not the heater hoses? Or is that not what you meant?

You want it on those if possible, as they will warm quicker than anything on the radiator side of the system, and keep warm whilst running.

[Budgetbond]

Thanks Brian yeah when looking into layouts on similar car engines to mine the reducer was either located close to the heater hoses (I know it's generally regarded as preferable) or the further side of the engine, I did opt for the latter for ease of fitting it, and for other components location too, it's quite well setup, and handy, I also slightly figured but maybe incorrectly, that it's coolant supply could be hotter as it had had time to run through the whole engine first?

However my lpg doesn't switchover for definitely the best part of a mile (seq multipoint) did u previously state that yours kicks over in less than half a mile and this should be the norm?

[Brian_H]

Depends what you set it to really - Newer kit will allow setting lower temps, though much below 30 degrees isn't a good idea because cold start enrichment could still be in effect, as well as possibility of reducer getting too cold to work effectively, possibly causing damage to either it or the injectors in severe cases.

Mine is set to 30 degrees I think on all 3 cars, and that generally will switch by the time I'm upto the dual carriageway which is around a mile from my front door when its cooler temp outside. Summertime its much quicker. That said, I'd rather the petrol injectors got a little bit of flow every time they started, just to keep them clear. Though given the current lack of working stations here, I've ended up back on petrol a couple of times recently when I've miscalculated how much was left in the tank.

Where do the hoses you have plumbed into actually go to/from? The heater should also get a good flow from the pump, which should help with keeping the vapouriser warm.

[Budgetbond]

Yeah mines set to 20C now, but it doesn't seem to struggle at that temp even over winter, I can't remember what it was set at last summer but I've generally experienced switching over at not much less than a mile.

Mines plumbed into what I assume is the engine return hose back to the reservoir after the water pump, but I'll take a further look at it actually, but it is plumbed into quite a convenient location really.

Don't suppose there s much more I can practically do without rechanging things around now.

[LPGC]

If you've driven the best part of a mile engine coolant should be well above 20C so there's not much surprise that it runs OK when it's first switched to gas if the reducer is well above 20C.

Next time the engine is flat cold before you start it connect the LPG software and read reducer temp and injectors temp readings, also if you can look at OBD live data and read engine temp. Since the engine is cold those 2 or 3 figures should agree, if they don't agree then the spec of one of the sensors (likely the reducer temp sensor in this case) may not be correct for the LPG ECU, so although you've set it to switch to LPG at 20C the reducer may actually be a lot warmer than 20C when it switches to LPG.

I forget what LPG reducer you have fitted (and which reducer temp sensor)? In LPG software settings what reducer temp sensor do you have selected?

[Budgetbond]

Yeah Cheers for the tips Simon was thinking similar from your previous comments so you reckon it should be kicking in quicker than a mile, id prefer that too.

My reducers a stefanelli if I can remember properly think it's like a tommasetto copy, and the temp sensors just a plug and screw into it think 2.2 ohms what I selected.

I've not noticed any temp readings that ve looked totally out of sync, but yeah ve wondered if knocking down the kickover temp even further to 15/18C mite make a difference.

[Gilbertd]

I'd say that is too low and you could freeze the reducer. Getting it plumbed in at the right place will have more of an effect. I've got workshop manuals for both MR2 Roadster and Gen 7 Celica, both using the same 1ZZ-FE engine that you have but neither show a diagram of the coolant flow. There will be a bypass for the coolant when the thermostat is closed, usually through the heater so you start to get heat out of it almost immediately the engine is started. That is where you want to plumb the reducer.