Audi A5 TFSI LPG conversion or NOT

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Autogas1985
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Audi A5 TFSI LPG conversion or NOT

#1 Post by Autogas1985 » Thu Sep 24, 2020 12:01 pm

Hello,

I can’t make up my mind and was given different reviews on LPG conversion for Audi A5 TFSI S (2016)line special edition 1.8 litre art. It has direct injection engine with CJEE code.

My research into the matter shown that I could install Prins VSI-DI system. It would take at least 2 years to get the money back.

Would the car work fine and is it worth it?

Thanks in advance for your responses and time.

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Re: Audi A5 TFSI LPG conversion or NOT

#2 Post by Fox vehicles » Thu Sep 24, 2020 4:42 pm

Hi, the Prins Vsi system is pricy but does work very well. The problem you will have is Prins is not available as a self fit system, especially Di so would have to be done by a (Prins) approved installer. This is important for the warranty and technical backup if required. But it does come at a price of course; typically a 4cyl Prins Di conversion will be in the region of £2200. Whether or not it is worth it is a difficult one to answer and I guess depends on how many miles a year you do, how much you pay locally for LPG and how long you plan on keeping the vehicle. On a plus side the Di Prins systems use very little petrol unlike so of the others.
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Re: Audi A5 TFSI LPG conversion or NOT

#3 Post by Autogas1985 » Fri Sep 25, 2020 8:04 am

Thank you for the information.

What is the likelihood of developing petrol injector problems or any other issues related to the car being converted to LPG.

Might be anyone has similar conversion done and can share their experience.

P.S I have read all I could find on the forum, seems like this type of conversion is quite rare.

Many thanks.

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Re: Audi A5 TFSI LPG conversion or NOT

#4 Post by Fox vehicles » Fri Sep 25, 2020 4:30 pm

Hi the Di conversions are certainly nothing like as common as an indirect conversion, there are a lot of reasons for this, not least that these engines haven’t been around for anything like as long. Then the fact that not all engines have systems available and not all LPG converters wish to take the jobs on and the conversions tend to be more expensive, etc, as I say lots of reasons. From my experience with Di the petrol injectors are not an issue providing the correct system/setup is installed. I visited OMVL, Italy in 2014 for training on their Di system and again to BRC, Italy in 2018, when speaking to the technicians there, they all agreed that the petrol injectors 'melting' was not an issue. The biggest problem they have when developing these kits is turning the petrol down low enough to introduce enough LPG to make the conversion worthwhile. Prins seem to have mastered this by using pulse width modulation to fire the gas injectors, the same as the petrol systems do, and this allows more précis fuelling and means they can reduce the petrol down to something like 3% usage whilst running on LPG, which is pretty amazing when some systems are using 30%. It will probably be difficult to find people running on these systems to talk to as there is nothing like as many, as we have already said, but if I can think of anyone who is up for it, I will give them a nudge towards the forum :wink:
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Re: Audi A5 TFSI LPG conversion or NOT

#5 Post by LPGC » Fri Sep 25, 2020 5:15 pm

There's a big difference between Prins VSI-DI systems and Prins Direct LiquiMax systems. VSI-Di is a port LPG injection system for direct petrol injection engines, Direct Liquimax uses petrol DI injectors to inject LPG in the same way as they would usually deliver petrol.

Similar to what Mick said, one of the challenges for Prins VSI-DI systems is that when petrol injectors are flowing a little petrol at the same time as gas injectors are in operation, particularly at low loads this implies gas injectors have to pulse for a shorter time than they would usually need to pulse for at idle. Gas injectors have a longer open/close/dead time than port petrol injectors (and especially compared to direct petrol injectors), if gas injectors are pulsed for too short a time they lose the ability to meter fuel consistently. The effect is similar to that we can see / play with on a port injected engine by having an engine idle on LPG when gas injectors might be pulsing for 3.5ms (if would-be petrol injector duration might be around 2.7ms, but petrol injectors at this moment are not pulsing at all because the engine is idling completely on LPG)... On such an install if we dial in (say) 1.5ms of petrol addition to be active even at idle the gas injector might need to be pulsed for only 1.5ms (because the petrol injector is now delivering 15/27ths of the fuel the engine needs to idle and the gas system only has to deliver 12/27ths of the total fuelling) but the gas injector will probably be incapable of accurately metering fuel at such low pulse duration (depending on type of injector, nozzle and pressure... but most gas vapour injectors are going to be well below the pulse duration at which they start to become linear/consistent at such short pulse duration). We could increase the duration that the gas injector needs to pulse for under these conditions (by decreasing nozzle size and/or playing with gas pressure) but then if the system is setup to still only supply 1.5ms of petrol fuelling at high loads the gas system probably won't be capable of supplying enough gas for the engine at high engine loads.

PWM is relevant in two contexts.... There's the PWM of direct injectors that can be pulsed several times during a cylinder's single full 4 stroke cycle (when in comparison gas vapour injectors are only going to want to pulse once or twice per cycle) and there's the PWM of the hold state of peak and hold gas injectors (to allow injector solenoids to open quickly by using heavy electrical current to get them open but prevent burning solenoid coils out by lowering electrical current flow when they are open for the duration they need to be open).

Any VSI-DI type system that interfaces to a petrol DI system (master/slave) will need to be able to handle the specific voltages of pulses to DI injectors on that particular make/model of vehicle, properly emulate the DI injectors and properly interpret the PWM of direct injection pulses (add them up for each cycle) to allow calculation of a single gas pulse.. Which means at least different firmware and maybe sometime different electronics to suit different vehicles, preventing the firmware and/or electronics from being fully generic or compatible with every DI vehicle.

At first consideration Liquimax might seem to allow a more generic approach, one that simplifies the challenges to just a plumbing challenge (if you've got LPG in fuel rails to DI injectors at the same pressure as petrol would have been in fuel rails to DI injectors the fuelling is going to be close to what it was on petrol anyway).. But there are problems associated with plumbing, fuel changeover (switching between petrol/LPG/petrol), cold start problems, hot start problems, extra and vehicle specific electronics being necessary anyway. Some vehicles have a 2 stage pressure control system for the high fuel (petrol) pressures involved with DI (lift pump / high pressure pump), the petrol system inextricably links lift pump and high pressure pump control, the link implies that at least a vehicle specific electronic fix would be necessary when the engine is running on LPG and lift pump pressure doesn't relate to fuel rail pressure as the existing expect to see/control. Credit to Mick at FoxVehicles for Info on DI 2 stage pressures and the 'link' issue! I think we last discussed DI systems a few weeks ago on the phone.
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Re: Audi A5 TFSI LPG conversion or NOT

#6 Post by Gilbertd » Fri Sep 25, 2020 6:05 pm

Fox vehicles wrote:
Fri Sep 25, 2020 4:30 pm
It will probably be difficult to find people running on these systems to talk to as there is nothing like as many, as we have already said, but if I can think of anyone who is up for it, I will give them a nudge towards the forum :wink:
The other reason they won't be on here is this forum tends to be found by people that have a problem and want to try to sort it themselves, those with a properly working system (and a lot without, they've just been told that the problem they have is normal when running on LPG) are unlikely to have need for, or any real interest in, a forum.
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Re: Audi A5 TFSI LPG conversion or NOT

#7 Post by LPGC » Fri Sep 25, 2020 9:39 pm

Gilbertd wrote:
Fri Sep 25, 2020 6:05 pm
The other reason they won't be on here is this forum tends to be found by people that have a problem and want to try to sort it themselves, those with a properly working system (and a lot without, they've just been told that the problem they have is normal when running on LPG) are unlikely to have need for, or any real interest in, a forum.
Although there have been a few on forum with problems with Prins VSI2 systems and I am regularly contacted (phone) by people with VSI2 systems who would love to bring them to me to have them fixed (from as far as Scotland and Cornwall) except VSI2 and derivatives are the only systems I can't fix because I don't have access to software which only Prins dealers are allowed. I reckon Prins shot themselves in the foot with the closed shop system, their dealers are probably the least likely bunch of installers to set them up properly in the first place or fix problems after-market. Probably because at the outset Prins set out to have a dealer network of garages that were 'established' before they started converting vehicles to LPG and the average garage is far better at fixing existing nuts and bolts stuff than at designing and setting up a fuel system. I'm still a better bet at fixing a Prins VSI1 issue than most Prins dealers though lol ;-)
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Re: Audi A5 TFSI LPG conversion or NOT

#8 Post by Fox vehicles » Sat Sep 26, 2020 8:33 am

I’m prins approved, so have the vsi 1/2 software and hope I don’t fall into the categories above 😁 happy to look at any problems people may have. Prins is a bit of a closed shop as you say, I can see what they are trying to achieve with that, it should be a network of helpful, knowledgeable installers that know how the system works, and have access to the technical support supplied by the manufacturer. It also means that all the components supplied by prins are registered and have a comprehensive warranty. This idea works, but comes at prins prices 😉 some customers want that, some just want a good system installed properly with backup from there installer 🤷🏻 It would be nice to think that all Installers Supply that, whatever the system, but as we know this is not always the case. I never encourage customers to have prins over, say aeb or BRC, the choice is there’s. Unless it’s Di and then the choice is limited. As someone clever once said, “do what you love, and love what you do” I find with that mantra I have happy customers, which means I’m 😃 what ever systems I’m working with 👍
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Re: Audi A5 TFSI LPG conversion or NOT

#9 Post by LPGC » Sat Sep 26, 2020 5:02 pm

Fox vehicles wrote:
Sat Sep 26, 2020 8:33 am
I’m prins approved, so have the vsi 1/2 software and hope I don’t fall into the categories above 😁
No mate you don't fall into the categories I mentioned above!
I didn't know you did VSI2 but now that I do I'll point people with VSI2 problems to you and be far more confident that you'll sort them out than the average dealer :-)
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Re: Audi A5 TFSI LPG conversion or NOT

#10 Post by Fox vehicles » Sat Sep 26, 2020 10:15 pm

Cheers mate 👍
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Re: Audi A5 TFSI LPG conversion or NOT

#11 Post by bonny » Sun Sep 27, 2020 8:51 pm

Just noticed this thread, so thought I'd chip in as I have a Skoda superb with a 1.8TSI engine converted to run on LPG. Not sure its the same engine you have but is definitely Direct Injection.

It runs very well, but does still use approx 30% petrol (it's not a Prins system) however, I was doing a lot of miles when I had it converted so it was still worthwhile. No problems in 18 months plus of use.

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Re: Audi A5 TFSI LPG conversion or NOT

#12 Post by LPGC » Sun Sep 27, 2020 11:08 pm

One aspect of converting a direct petrol injection engine using any kind of port injection system is that you lose the advantage of direct injection that the engine was designed to take advantage of.

At light engine loads it would probably use more fuel with port injection than with direct injection anyway - Albeit of course half price fuel instead of full price fuel!

But still, if the main advantage of direct injection is increased economy at light loads or fuel injection into a 'pocket' in the piston for localised (in the pocket) correct mixture while general cylinder wide mixture is lean (which direct injection can allow)... Then even though we might expect a 15% economy increase (the 30% petrol contingent becomes an additional 30% LPG contingent while LPG is half price of petrol) we may be surprised that the savings are an additional 15% from running entirely on LPG instead of on 30% petrol and 70% LPG. Direct injection may increase low engine load fuel economy by 20% over port injection... Which could mean that if we managed to make a direct injection engine run entirely on LPG (half price fuel) instead of on 30% petrol and 70% LPG, instead of us realising a 15% economy increase we might only see a 5% economy increase. While at the same time running the DI engine of 30% petrol at low loads may protect expensive DI injectors from premature failure. In modern times (not talking about WW2 ME109's etc) one of the earliest common direct injected engines was in the old Mitsubishi Shogun, the electronics on this were simple enough that the engine could be converted using a simple LPG mixer system but most installers would know to warn the owner that doing such conversion, which meant no fuel flowing through DI injectors when running on LPG, had the potential to cause damage to the DI injectors by means of seeing them not flow any fuel when the engine is running.

The Prins Liquimax system (and similar systems from manufacturers that have gone bust) works entirely differently and sees LPG instead of petrol flowing through the original vehicle's DI injectors. Such systems all have their problems but so too do all port injection systems for DI engines. But at least the Liquimax type systems retain the direct injection aspects. In my view Liquimax' existence kind of implies that Prins acknowledge the issues of converting a DI engine using port injection tech.

I believe that most of the port injection systems for DI engines could be improved if they were thought out and designed with very good LPG injectors in mind. Prins may have an advantage over other manufacturers in this respect because Prins systems employ the very good Keihin injectors while most other DI port injection system manufacturers will have other injectors in mind during the design stage. But Prins do not own Keihin, they merely use Kehin injectors by default and any manufacturer of ECUs could design their system to use Keihin injectors. Arguably Prins ECUs have always been very basic and lacking in functionality compared to other systems, we (or I) could say that any system would have earned a better reputation than Prins when (back in the day a lot of years ago now) they supplied their systems with Keihin injectors along with their own (much more advanced even at the time) ECU's compared to Prins ECUs.

During one of my last chats with the (then - I don't know if they still are) Prins importers/distributors a few years ago I was surprised by just how much behind the times this supplier seemed to be. They spoke of the advantages of the new VSI2 system over VSI1 in terms of ability to switch individual cylinders back to petrol during diagnostics and/or the setup process and ability to dial in correction for rpm. At the time they mentioned these 'advantages' they had already been considered by most installers of almost any other system available on the market to be the bare minimum of functionality. Every AEB based system and every Polish / Cheq / etc system had already offered such functionality for many years, just that the Prins dealer used to VSI1 thought this was a great upgrade and only because they were behind the times and unaware of what every other system had already provided for many years. I have had a Prins dealer/importer in Huddesfield describe to me how they removed what I would consider a perfectly suitable system from a vehicle and supply/fit (at great expense to their customer) a VSI1/2 system simply because they knew so little about getting good results from the other make system. If that customer's vehicle had come to me I reckon I could have sorted all it's problems in I expect at most an hour of my time and most likely without replacing any components, I would have expected to charge £60 but they will have charged around £2000 and my results would have been better. I work with all systems/ECU's except VSI2 (which I don't really care about) and except Liquimax (which I do care about) but when it comes to ECU's I reckon Prins has a poor track record, only got as far as they did with their very poor ECUs because of Keihin injectors. In my mind KME make the best port injection ECUs ever made, and they take some advice from me when it comes to updates. If I suggest a new facility it seems to become part of the next firmware / software update and all controls work as expected / described, with almost any injectors including Keihin. There was a Prins system that didn't use Keihin injectors, the Lima system was one of the worst ever made. If we went back in time to a time when most LPG injectors were slow and unlinear while Keihin were as they were at the time, but made a system using a better (than Prins) ECU and Keihin injectors it would beat the Prins system in every respect. But it may still not beat a modern system with injectors that has injectors that are not Keihin because one drawback of having such chunky Keihin injectors is that they cannot always be fitted in the best location about the engine without increasing the negative of pipe lengths.
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Re: Audi A5 TFSI LPG conversion or NOT

#13 Post by Autogas1985 » Mon Sep 28, 2020 12:01 pm

Thank you all for your information.

I have bought this convertible car to be used as a good weather car. Taking into account possible issues will most likely leave it as petrol. It’s a shave as all my other cars are LPG and running cost is so small I can’t even feel it .

Thanks

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Re: Audi A5 TFSI LPG conversion or NOT

#14 Post by Fox vehicles » Fri Oct 02, 2020 9:43 pm

Just pop this one in for the latest offering for Di engines from Prins, note the less than 5% petrol usage, that's what we want :wink: :D

"The Prins VSI-3 DI LPG system offers a universal solution for a wide variety of vehicles of the latest automotive technology, complying with the latest global emission standards like Euro 6D WLTP and certifications like R115/EPA. The system is of high quality, extremely efficient (petrol use <5%), higher performing, providing a smooth driving experience, just like a normal petrol car. By driving on LPG (Autogas) one saves fuel costs, sometimes hundreds of Euro per year, and saves the environment by lowering CO2 (21%) and particles emissions (up to 95%). The system is available now, worldwide, at the official Prins installers"
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Re: Audi A5 TFSI LPG conversion or NOT

#15 Post by Autogas1985 » Sun Oct 18, 2020 10:05 pm

Fox vehicles wrote:
Fri Oct 02, 2020 9:43 pm
Just pop this one in for the latest offering for Di engines from Prins, note the less than 5% petrol usage, that's what we want :wink: :D

"The Prins VSI-3 DI LPG system offers a universal solution for a wide variety of vehicles of the latest automotive technology, complying with the latest global emission standards like Euro 6D WLTP and certifications like R115/EPA. The system is of high quality, extremely efficient (petrol use <5%), higher performing, providing a smooth driving experience, just like a normal petrol car. By driving on LPG (Autogas) one saves fuel costs, sometimes hundreds of Euro per year, and saves the environment by lowering CO2 (21%) and particles emissions (up to 95%). The system is available now, worldwide, at the official Prins installers"
Thank you for the info. I will get in touch with you to discuss the options further.

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