You've twice mentioned the fault being ambient temperature related, no faults seem to occur when the weather is warmer.

What readings are you seeing for intake air temperature and do they agree with actual air temperature?

Really IAT shouldn't make much difference because MAF sensors are self compensating for intake air temperature. Yet all MAFs have built-in IAT's...

Gilbertd wrote:

CNG conversions are a common alternative to LPG (Propane) in many European countries, particularly Italy. There's a number of trucks running on it in the UK now too. Energy density of Methane is slightly better than petrol or diesel (see https://en.wikipedia.org/wiki/Energy_density) although you will use slightly more of it due to the stoichiometric ratio (see https://en.wikipedia.org/wiki/Stoichiometry).

The other downside is the tank, Propane needs a tank capable of storing a liquid at around 10 bar (145 psi), so fairly simple to construct, but a CNG tank needs to be able to store the gas at around 10 times that, LNG needs an even greater pressure.

There's little difference in peak torque or bhp between LPG and petrol but engines run on NG make less power than engines run on LPG.

I should define a few terms to make sure the rest of what I write makes sense. CNG is compressed natural gas (NG), LNG is liquified NG.

One downside to LNG is that it has to be kept at cryogenic temperature... If you needed to store it (store could mean just park a vehicle for a week without using it) there'd need to be some measures taken to keep it cold or the increase in temperature would mean an increase in pressure that could burst any tank. I believe that in practice they have a vent valve which allows a little NG to escape to atmosphere and the evaporation keeps it at cryogenic temperature during such storage. But that's not environmentally friendly because NG is one of the most potent greenhouse gasses, much worse than CO2.

LNG is used on trucks etc but CNG is usually better suited to cars (mostly due to the above reasons). If we have NG delivered to our homes (which we do if we have piped gas to the home) we could easily buy a CNG compressor and fill CNG converted vehicles at home. I have looked into this. CNG tanks are difficult to source in the UK, in fact it seems easier to buy a CNG compressor than it is to buy a CNG tank in the UK! Running a vehicle on CNG is probably the cheapest way of running a vehicle... It's just that with the lack of CNG filling forecourts the only place we'd be able to refuel with CNG is at home using our ow (expensive to buy) CNG compressors. I would have already done it (fitted a CNG tank and CNG pressure reducer to one of my cars and bought/fitted a CNG compressor at home) if tanks were more readily available.

Morat wrote:

300 miles from a Tesla 3 is ambitious. You'd need a full battery. IIRC even the long range version tops out at 350 miles (in ideal conditions of course). Tesla recommend that you keep the battery between 20 and 80% whenever possible to increase the battery life, so most of the time the range is much less. Of course, most of the time you don't need 300 miles but it can't be a nice feeling to imagine you're pushing such an expensive component when you do.

I personally would like to check out a Tesla, but I now WFH so the only time I need to drive is usually a dash into York or a road trip 3 or 5 up for a long way. So, I think the Simon's home LPG pump is FAR more interesting!

Maybe worth looking into yourself Miles? Contact a few local-ish gas suppliers, tell them how much you'd expect to use, ask them how much for 47kg bottles delivered to your door, see if you can haggle the price down. Then you just need a pump... You could buy a pump tomorrow from a well known supplier (MIck at LPGAutosupplies, ex TinleyTech) for £600+VAT. If you made the calls on Monday you could be set up ready to refill at home by Tuesday or Wednesday and for a similar cost per litre to refilling at Morrisons.

There's a guy on LPGforum who reckons he uses a £30 car electric petrol pump to pump LPG from bottles into his car LPG tank, I'm not sure if that really works or if it does work how reliable it would be but I've thought about trying the cheap pump myself.

If electric vehicles really do take-off then we could expect forecourts that sell petrol and diesel to decrease in number, we may even see the day when petrol/diesel are difficult to buy and people with petrol/diesel cars have range anxiety. But even then, or even if we couldn't buy petrol or diesel at all, as long as people use LPG for heating and it isn't illegal to run vehicles with engines we would still be able to run our vehicles on LPG if we refuel at home.

With an extra LPG tank fitted my car will do 700 miles on a single fill of LPG. I made my extra tank quick fit / quick remove, I removed it today because I needed the luggage space so at the moment my car only has 350 miles range on LPG. The extra tank is now sat in the yard and it's full. If next week I needed to refuel but all LPG forecourts were out of action I could still put the extra tank in the back, connect it up and drive 350 miles on LPG. In fact I've got loads of tanks in the yard, mostly new ones, any of them could be used as the extra tank and I could carry several of them in my car. I've also got a full 70L forklift tank and a full 18kg propane (caravan) tank - I could easily make a short (3ft) pipe with correct fitting on one end to connect to any of those tanks and quick-fit (hanson coupling) fitting on the other end and run my car from any of those tanks.

Years ago I used to fix local Calor depot's fleet of LPG converted vehicles and got to know a couple of their delivery drivers. The delivery drivers sold me LPG in red bottle forklift tanks, 10 tanks at a time at a price that worked out at around 11p per litre. They'd park on the top road outside my place and we'd simply roll the full bottles downhill 20yards down the driveway into my yard, carry the empty bottles back up to the lorry. I didn't bother trying to pump from the red tanks into my car tank, I just rigged a pipe into the luggage area of my car and carried 2 red forklift bottles in the luggage area. Around 35litres in each of those (small) forklift bottles.

Bolt wrote:

If we start with a natural gas fired power plant, and 100 cu litres of CNG.
Burn that in a furnace to boil water in a heat exchanger, make steam, turn the turbine to generate electricity.
Best case is 60% efficiency and only if you can use the waste heat to do something. (as low as 33%)
https://energyeducation.ca/encyclopedia/Natural_gas_power_plant
So, 40 of our Cu litres gone to heat at the plant.
Now we have electricity at about 500kv which has been stepped up there using transformers.
These are pretty good, however we go through no fewer than 4 to go from the plant to the rural grid, to the local grid and to your house. we will through in transmission losses here as well so lets call that 10%, but it can be much higher.......So, kiss off some more CNG..
https://blog.se.com/energy-management-energy-efficiency/2013/03/25/how-big-are-power-line-losses/
Now, we have a battery charger coming in at about 80% on average, so more heat and more wasted energy.

Batteries themselves are not 100% efficient and degrade as they are cycled, so average over a 6 year life cycle? call it 80% with 20 % being turned to heat in the battery.
Electric motor and controller? 90% is generous, so another 10% loss to heat.
I have used the average losses here and leaned toward very conservative numbers.
Even so, you are kissing off more than 50% of the electrical energy produced at the plant before
it even sees the EV. other types of plant, like coal are far less efficient.
Not my idea of an environmentally friendly solution.
Question for LPGC: How much better would it be to just burn the CNG in a converted vehicle?

As much as I love engines they're only around 30% efficient and the fuel has to be refined and transported to forecourts. But the infrastructure is already there, no need to build more power stations, upgrade the electrical grid or source lithium.

Gilbertd wrote:

From what I've seen the idea behind it being a renewable energy source is that by producing it by hydrolysing water using electricity from renewable sources, you've got a zero carbon fuel.

Yes, so if we ever have abundant clean electricity we can also have abundant clean burning hydrogen. Then maybe we could all go back to ICE cars and run them on hydrogen hehe.

Not wishing to steer the thread off topic but LPG has been mentioned and on that subject - It's not difficult to get set up with the ability to refuel at home, without needing to have a bulk storage tank and at a similar cost per litre as refuelling at Morrisons...

I recently contacted a local bottled gas supplier (in Doncaster 10 miles from me), they'd be happy to exchange bottled gas at my door. I'd go with 47kg bottles (biggest bottle best value), no minimum order (they'd deliver 1 bottle or any number of bottles at a time), free delivery, usually next day delivery. They're not bothered what use I have for the gas.. When I first spoke to them I mentioned using it for heating the garage but when it became clear they didn't seem concerned what I used it for I told them I convert vehicles to LPG for a living and 'might' pump some into my car. In fact it seems vehicle use may help negotiate a lower price per refill because if you're using it in your car you're likely to be using more gas than someone who just uses it for heating (especially in summer) and there are discounts for heavier users (and if you're using a bottle per week you'll be a relatively heavy user). They were talking £90 per 47kg bottle exchange until I said I know of others paying £75 for one 47kg bottle per week refill per week and that I'd expect to use a 47kg bottle per week even during summer, then they immediately agreed to £75 (maybe I should have tried £65!).

£75 including VAT for 47kg of gas, free delivery, works out at 81.5p per litre which is 1.8p per litre more than Morrisons but refuelling at home means no need to make any detours to refuel.

They'll only refill/exchange their own 'brand' tank (same design 47kg bottles as Calor, Flogas, etc, just with their logo written on the side instead of the more common Calor/Flogas logo). £65 surcharge per bottle I want to keep here, keep their bottle for as long as I want, surcharge is refundable if I let them take their bottle back. I'd probably go with 2 x 47kg bottles and order a next day exchange as soon as 1 bottle was empty to keep at least 1 partially full tank here at times.. See how it goes with 2 bottles, maybe end up having 3 bottles.

Need a pump.. LPGAutosupplies sells a pump for £600+Vat, a bit expensive so I'll be looking into other pumps (hence why I've not done it already). No rush for me because I am well served by local LPG forecourts but I'd like to get set up with this as an example to others (not on this forum but on other forums).

I could have home refuelling set up and running 2 working days after contacting the gas supplier for the gas and LPGAutosupplies for the pump.

All considered with the cost per litre being very similar to Morrisons and the surcharge on the bottles being refundable, even if I had a Morrisons next door the only real setup cost would be the cost of the pump.

Ideally would want to set up some sort of stand to make it easy to invert the bottle in use (bottle must be inverted to pump the liquid gas out of it), they're heavy with an empty weight of around 34kg, plus 47kg of gas when full makes full weight 101kg. But I'd start by just laying the bottle on it's side and pumping gas out until it was half empty, maybe put a couple of bricks under the bottom end to pump it down to a total weight of say 45kg then manually invert it to pump the last 11kg out of it.

Slightly off subject again - It's usually easy to add an extra LPG tank to a vehicle (though it will usually take up luggage space). Last year I added a 2nd tank to my own car (not a Rangerover) giving total range on LPG (driving economically) of around 700miles. The 2nd tank is quick fit / quick removal, connected to the car's original LPG setup using quick connect/disconnect hanson fittings (like airline fittings). When not fitted there's no sign of any tank fittings in the luggage area, the hanson fittings it connects to hide away behind the access panel to offside rear light bulbs. I don't usually have the 2nd tank fitted because I don't usually need so much range on LPG, I can leave it in the yard full of gas until I want the extra range (like when I tow my caravan to Cornwall). Again not difficult to set up, any tank (that will fit in the luggage area) can be used, could use a second hand tank. Of course once the car is setup with the quick fit tank modification it's no more difficult to carry 2, 3, 4 extra tanks than it is to carry 1 extra tank, the only restrictions are space and weight (but 100 litres of LPG including it's tank will only weigh around 100kg), when the connected tank is empty just connect the quick fit fittings to a full tank. My vehicle is an 8 seater people carrier but the rear seats can be folded up to make it a 5 seater with a massive luggage area, it would be completely unnecessary, excessive and maybe a bit ridiculous but there is nothing stopping me from carrying (say) 3 x 100 litre tanks in the luggage area and having 1400 miles range on LPG (plus 350 miles range on the full tank of petrol). Each additional tank would only need to have a length of pipe fitted to it's fill port, output port and a hanson fitting at the end of each piece of pipe to make it useable as a quick fit tank in my car. I could fill up at home from red bottles at same cost of filling Morrisons, fill with 360 litres of LPG, drive for 1400 miles without refuelling and/or refuel at any forecourt that sells LPG for 1400 miles range in around half an hour on the forecourt. Even if I ran out of LPG I'd still have a full tank of petrol. Unless I removed the petrol tank to fit an extra LPG tank in it's place and make my car LPG only.

For alternative fuels (every fuel that isn't petrol or diesel) the important factors are cost of the vehicle, cost per mile, ability to refuel when necessary (enough 'forecourts' or places to refuel), speed of filling up (nobody really wants to spend an age sat on a forecourt). One aspect can offset another, e.g's. you don't need as much range if there are places to fill up everywhere and speed of filling is very quick as with petrol / diesel. Or on the flip side if you'd got great range you're less likely to have range anxiety even if there are relatively few places to refuel... especially if you can refuel at home. EV owners who always recharge at home at cheap prices will be smiling but not smiling so much if they need to do a long journey and recharge away from home at similar cost per mile to someone refuelling an ICE car who can refuel in a fraction of the time for much better range. I'm biased anyway because I convert vehicles to LPG but even if I wasn't still involved converting vehicles to LPG I'd still see it as having the best set of compromises because almost any petrol vehicle can be made to run on it, it's a fraction of the price of petrol, places to refuel aren't as numerous as they once were but I can refuel at home for same cost as refuelling at a cheap forecourt if I wish, it is easy to add extra range (and with extra range I don't need to worry about refuelling), refuelling isn't much slower than refuelling with petrol or diesel. Cost per mile running on LPG can even be cheaper than running a like-sized EV if charging the EV away from home and if doing anything like the kind of mileage that would cause range anxiety for an LPG user (even with just one tank fitted) in an EV the EV will probably need to be charging away from home. Hydrogen might be a great idea but it might take legislation forcing forecourts to sell it before it could take off, might expect early hydrogen powered cars to have similar or less range than an EV but with no ability to refuel at home. If we were all given a free hydrogen car tomorrow we wouldn't be able to use them.

romanrob wrote:

Lpgc...right...free to sell and buyer pays premium. No vat on the car tho, obv.
Collecting cars seem to have quite a good formula in terms of detailed photos and full disclosure

You've done a great write-up on the ad.

I suppose no seller fees can make for a lower sale price (less the buyer's commission) and whether the seller or the buyer has to pay fees won't make a lot of difference to what the buyer ultimately pays in total - Your car's worth a lot more than £600 but if someone were to sell a £600 car on the site they'd be giving it away for free if the seller paid the commission, so a seller might sell for less on this site versus a site that charges the seller the commission.

I'm not clear on whether the minimum buyers fee of £600 is £500+VAT or £600 +VAT.

Are you committed to sell to the highest bidder?

Buyer has to pay at least £600 or 6% to the auction site on top of the agreed sale price plus VAT?

The equivalence ratio readings are the mixture readings to use - bank1 S1 and bank2 S1. The voltage/current readings aren't really useful.

You've said your lambda equivalence readings at cruise remained close to 1, which is a good sign.

If you drive only during those (cruise) conditions do you get any error codes / MIL come on?

If you drive at other engine loads (with constant throttle position) does equivalence ration stay close to 1? Do you get any error codes / MIL come on under any of those conditions (if so what conditions e.g. constant 30mph very little throttle, 80mph constant throttle)?

Even if the equivalence ratio stays close to 1 you can still get fuelling error codes if fuel trims are at an extreme to achieve equivalence ratio close to 1. It would be a good idea to check LTFT B1, LTFT 2, STFT B1 and STFT B2 in various driving conditions. I would expect STFT's to swing by around +-12% during accelerator pedal movements (that's normal) but what are all those readings at constant throttle at various engine loads?

You previously mentioned fuel pressure readings (which I said seemed normal). The fuel systems on 4.2 supercharged Rangerovers reacts to fuel pressure readings - Say the fuel pressure at a certain engine load is supposed to be 450kpa, if the actual fuel pressure reading at that engine load is only 400kpa the system will react by increasing injector pulse length to compensate for the slightly lower fuel pressure than expected. On a conventional / old-skool fuel injected engine the need to adjust injector pulse duration because fuel pressure is low would be reflected in fuel trims but on this model vehicle the low fuel pressure probably won't be reflected in fuel trims because instead it reacts to the low fuel pressure by compensating the pulse length.. But the fuel pressure 'fiddle factor' can only work properly within a certain range of deviation from correct fuel pressure.. So it's important that the fuel pressure isn't too far from the norm across the entire engine load range or incorrect fuel pressure could cause OBD error codes / MIL light. The following sentence may be a bit too much info but if you want to understand the way it compensates for under/over fuel pressure - Behind the scenes the system compensates by comparing the square root of fuel pressure, so let's say (hypothetically) that the fuel map (and injector pulsed duration) for a certain engine load is set up to be correct for a fuel pressure of 500kpa above expected manifold pressure (the amount of fuel an injector will flow is effected by it's pulse length, fuel pressure and manifold pressure... fuel pressure minus manifold pressure because we have fuel pressure on the input side of the injector and manifold pressure on the output side of the injector). The square root aspect is a physics aspect - If we double the pressure of a liquid through a nozzle (or injector) it will flow 1.402x the amount of the original pressure. So if the map dictates an injector pulse length of (say) 10ms at a certain engine load for an expected fuel pressure of 500kpa, if the actual fuel pressure reading is only 250kpa (half of 500kpa) then we might expect the system to respond by adjusting the pulse length from 10ms to 14.02ms and for the fuel trims to be the same as they'd be if fuel pressure were 500kpa and injectors were being pulsed for 10ms.

Summing up, if you identify a certain condition / engine load that cause the MIL to come on - what are the equivalence ratio readings, fuel trim readings and fuel pressure reading at that engine load?

I don't have much to suggest that could be the underlying cause of the error codes at this point but assuming you haven't just let it idle after resetting an error code and/or fuel trims and assuming you're correct about no vacuum/boost leaks and the advanced evap system... if I had to hazard a guess it would be the MAF. But if it were mine before buying a MAF I'd be gathering the extra data I outlined above.

I'm sorry I overlooked your post #20,

If lambda equivalence ratios are close to 1 that's a good sign there isn't much wrong with the wide band probes.. and there won't be any misfires if that reading is close to 1 either because a misfire reflects in a lean reading from lambda probes so that's another good sign.

Adding to what I said in my last post, similar concept to not letting the engine idle for too long before going for a drive.. when driving don't keep to the same engine load for too long either. All the time you're at a particular engine load the long term fuel trims are steered by short term trims but if short term trims reach an extreme (say -25% or +25%) the steering of long term trims stops and then if mixture is lean or rich you get a fuel trim error code. So one way of allowing long term fuel trims to be learned whilst not causing an error code is to drive only briefly at a certain engine load if short term trims are at an extreme at that engine load. E.g. Say you're doing 60mph at (I forget the gearing) 2500rpm in a certain gear, lambda equivalence seems good (close to 1 or command lambda) and short term trims aren't at an extreme then you could drive forever at that engine load and it won't bring a code on. But if you're at that engine load and equivalence ratio isn't close to 1 or close to command lambda and the short term trim reaches an extreme you'll get the error code... But before you got the error code the long term trim will have been steered a bit and if you'd changed engine loads before the error code was triggered you could go back to the same engine load and the fuel trim for that would be steered in the right direction a bit more. With enough little steers of the long term fuel trim for that particular engine load eventually the short term trims wouldn't need to reach an extreme to correct mixture and then you could drive at that engine load without triggering a MIL code.

p73990 wrote:

What name or letters would i look for that are the mixture readings in the ECU?

It's usually termed lambda equivalence ratio or equivalence ratio in most OBD scan tools.

There may also be a command equivalence ratio which is the mixture that the engine ECU is aiming to achieve for the given engine load conditions, for most off-boost conditions this is usually very close to 1 (which is 14,7:1 the chemically correct 'stochiometric' ratio for petrol), for high engine load conditions with mixture enrichment this may fall to 0.8 (around 11.7:1).

Very good, well done!

I've been away on holiday a few days so I'm late to see this thread but I've done plenty fuel system related work on Supercharged Rangerovers (I've converted plenty of them to LPG).

They have a returnless fuel system but fuel pressure is adjusted by electronics controlling the fuel pump... It could be termed 'on demand' fuel pressure. The engine management on them is very sensitive to vacuum leaks (including false air from a disconnected or failing cam cover breather, evap purge valve flowing when it should be closed, etc).

One unusual aspect of them - Say you've had an error code, then you reset the error code (which after some error codes will reset fuel trims)... If you then just start (after resetting fuel trims) and leave it idling the chances are you'll get fuel trim error codes. The way around that would be to clear error codes then not leave the car idling, instead start it up and immediately go for a drive.

With a basic scan tool you probably won't be able to manually reset fuel trims. But causing one of the more 'severe' error codes such as open circuit petrol injector then resetting error codes will reset fuel trims. I.e. If you want to reset fuel trims but don't have a scan tool with that function you can still reset fuel trims by disconnecting a fuel injector, let the system log the error code, then clearing the error code will reset fuel trims. But then don't forget to go for a drive immediately after starting the engine or you'll probably get a fuel trim error code anyway ;-)

A scan tool will show you fuel pressure... There's an electronic fuel pressure sensor built onto the fuel rail, there has to be one for the on-demand fuel pressure system to be able to read fuel pressure and control the fuel pump properly. Edit - Noticed you're getting 40>60psi, that seems about right to me, as memory serves my scan tools read between around 400 and 600kpa on most Supercharged Rangerovers depending on engine load.

The lambda sensors are wide band, any voltage reading from them is meaningless (a voltage reading from a wide band probe is meaningless without knowing how the 'pump' in the wide band probe is being controlled) but an OBD scan tool should be ale to tell you directly what mixture is, probably in terms of lambda (lambda of 1 means correct mixture, 0.995 slightly rich, 1.005 slightly lean). Mixture should stay close to lambda of 1 (which is 14.7:1) but go rich under boost conditions maybe down to around 0.8 at full engine output. The scan tool can tell you mixture because the engine ECU knows mixture, it contains a dedicated wide band lambda sensor control chip that 'homes in' on mixture by reading lambda voltage and knowing how much current (uA) it is applying to the 'pump' in the wide band probe.

Pleased to read that Gordon :-)

If I were to start reading again at the first post I might guess that it started fine from cold due to running open loop fuelling and as soon as it warmed up and switched to closed loop fuelling it ran poorly due to a duff lambda sensor.

Sometimes error codes can be misleading.. If the code doesn't point to an electrical issue such as open circuit SAI system maybe the ECU error detection assumes an SAI fault (because SAI is active) when there is a mixture issue?

Bolt wrote:

Well, Pulsed, but at what frequency? and at what point is a switched supply considered to be PWM?
In other words, if one was looking at the signal relative to B+, what would you normally see for pulse duration?
If it was not bucketing down right now, I would go check to see what I get.

I used the term PWM very loosely, I'd guess the usual pulse frequency of evap purge valves to be around 5 pulses per second (5 pulses of full battery voltage) and pulse durations of around 0.1 seconds. So not PWM in the usual sense.

Gilbertd wrote:

@LPGC, no it isn't a PWM signal, it is a permanent live directly from the fuse (via a splice) with the ground,either permanent or pulsed supplied from the ECU. So provided he is testing the voltage with respect to ground and not across the pins, it should show full battery voltage.

Yes of course, pulsed on the negative not the positive.

Could the 7v be a digital multimeter reading of a 12v PWM signal (so in reality the parts get expected voltage... but because the power isn't constantly on the multimeter reads pseudo average voltage)? For sure purge valves are quickly pulsed as opposed to being held constantly open.

Gilbertd wrote:

As Pete says, we drive on the left so the right hand is free to use the sword on someone coming the other way.

I've heard that somewhere, also heard it's because if your whip (right) hand is nearest the middle of a road you're less likely to whip someone at the side of the road. Makes sense if driving a manual car too as you keep your right hand on the steering wheel when changing gear.

On the main topic....Not sure about P38's but on most evap equipped vehicles evap purge valves are usually pulsed (rather than being just held open for long periods) and the PWM of the valve wouldn't be enough to upset fuelling (false air to lean / petrol vapour to rich) enough to cause a problem even if there were a problem with it, except for really picky systems like Jag engine'd L322's and certain Volvo's. But if the evap system is in doubt you should be able to confirm/disprove an issue by blocking the pipe to the manifold.

As an aside (still on topic but off on a bit of a tangent)...

For some vehicles (don't know if this would be compatible with the RangeRover's none standard OBD) it's possible to fit an AEB OBDuFix (universal fix) to allow the engine to run without a lambda sensor when the fuel injection system expects a lambda sensor to be fitted.

These units connect to the lambda sensor signal wire and to OBD, they read the fuel trims via OBD and if the fuel trim goes positive they emulate a rich lambda reading which then steers the fuel trim back toward zero (or emulate a lean mixture lambda reading if the fuel trims go negative). In this way they constantly steer fuel trims toward zero whilst not upsetting the petrol ECU because it sees the constantly flicking lambda voltage it expects and fuel trims always stay close to zero.

https://www.aeb.it/en/products/emulators/obd-emulators/

They were designed for the purpose of preventing petrol fuel trims reaching extreme negative or positive when converting a closed loop petrol system to run on LPG using an open loop or standalone closed loop LPG system (such as a mixer system or an early standalone LPG injection system). Not necessary if fitting a 'slave' type LPG system which bases it's fuelling on would-be petrol fuelling. I haven't fitted one for many years but there was a time when we offered customers 2 ways of converting certain vehicles (e.g. 4L Jeeps), either a mixer system (standalone closed loop system so when running on LPG for a long time petrol fuel trims would eventually drift to one extreme) or a more expensive sequential slave type system (which avoided the problem if calibrated properly)... These units could prevent poor starting and harsh running on petrol (due to very wrong fuel trims messing the mixture up after a long period of running on LPG) and they were a must on post 2000 4L Jeeps because they'd put the MIL on which would disable the cruise control when fuel trims reached an extreme.

Usually fitted on vehicles that do have a lambda probe fitted (no need to address fuel trim issues if the vehicle doesn't have fuel trims because it doesn't have a closed loop fuel system / lambda probe), so they don't emulate the lambda probe heater circuit but that could be emulated with a simple dummy load (bulb etc?).