Mark Lawton's Generalist's Repository

I had a Skoda Favorit 1.4 petrol in 1999, which I had bought some years before in 1994,and it was running OK on petrol, but being a bit of a “tinkerer”, I decided to do a project, and see if I could convert it myself to run on LPG.

Off I went to Hereford to buy my OMVL LPG DIY conversion kit. It cost me £350.00 in 1999. So the payback time was very fast indeed.

It consisted of a round tank, a multi-valve, the vapouriser, a solenoid, the in the cabin under-dash OMVL gas/petrol switch with combined fuel gauge, and a “giant polo mint” with holes in to distribute the vaporised propane into the air filter called a mixer.

The mixer fits into the air filter on top of the air-intake of the car, so that the gas is distributed into the manifold, and is burnt when it enters the combustion compression and ignition cycle of the four-stroke internal combustion engine.

When I arrived there I bought the kit, and I had a verbal rundown on what I should do.

I had to bolt the tank into the rear boot part of the car, using the brackets supplied, and provide an outlet for the double layered in and out pipework in “microbore” or similar, but thicker copper tubing, covered in a UPVC protective covering. I used a wheel type pipe cutter, and a pair of side cutters to strip the PVC layer back, and cut the piping.

So it was out with the drill and the “hole saw” to cut holes in my car for the pipe-work!

The inlet was from the tow bar, where the LPG filling point was going to be located in my case, and the outlet of still liquid gas from the tank to the vapouriser located within the engine compartment.

The Multi-valve mounted upon the gas tank serves as a non-return valve for filling, and as an outlet for the gas to the vapouriser which in my Case is in the engine compartment.

It also serves as a fuel gauge, as there is a mechanical indicator on it as well. There is a resistive output which also serves as a fuel gauge display in the car, this is sort of “OK”, but not accurate, due to the shape of the LPG tank.

Because the shape of the tank is non-linear, the fuel seems to drop quickly, halt a while, and then drop quickly. This is due to the tank having a low volume at the top curve, dropping slowly in the middle, and quickly at the bottom, because the curve at the top and bottom holds the least fuel, it drops quickly there, but in the middle where it is wider the fuel level drops slower.

Around the pipes leaving and going into the tank is a second “outer covering, which should go through the bodywork to the outside of the vehicle. In the event of a leak, any gas is vented outside the car from the tank, as an added safety feature.

When I got my tank I did bend the float arm so that it said I was low on fuel before it ran out, then I was always OK with my round 40 Litre tank.

The OMVL Multi-valve fuel gauge assembly was fitted to the tank, firmly bolting the assembly to the tank with the Allen screws, and the gasket supplied, remembering to fit the outside cover 1st, which catches any leaks, and vents them as mentioned earlier through the double cavity piping to the outside world.

I was aware that you need to know what you are doing, otherwise a leak could be created, although through experience with fitting a second bad gasket after removing the first one, resulted in the LPG dispensing pump not dispensing any fuel and cutting off, obviously detecting the leak I had put onto the tank!

The reason I was messing with this a second time again, was due to the fuel gauge being so inaccurate, and removing the multi-valve, to bend the float arm, and spoiling the original gasket, which caused a leak DANGER BEWARE If you are aware of this point of a good seal on whatever you do you will be OK, but BE AWARE of this point, as it can result in loss of fuel, explosion, asphyxia, or frostbite due to liquid gas evaporating and changing to a gas by latent heat of vapourisation! WARNING!

From the multi-valve the piping should be bracketed to the bodywork, following the brake pipes as a guide, and then the pipe emerges into the engine near the brake master cylinder.

From there the pipe goes to a 12V cut-off solenoid, which is turned on and opened to gas flow by the internal OMVL control switch, a 12V plus also goes to a second solenoid on the OMVL vapouriser. Having two solenoids is an extra safety feature to ensure when the gas is off, it is off!

I used a bit of glue to hold the spades on due to vibration, and prevent moisture ingress, but this was a bit OTT!

The gas enters the vapouriser, and it is turned from a liquid into a gas, where it then goes into the “polo mint”, or mixer.

Obviously, it would freeze up without being heated up, due to vaporising all of that liquid gas flowing through it; so how it does this is by taking a heater hose, and bypassing some hot water from the engine to the vapouriser, and back to the engine again, usually from the heater inlet, so that it never gets turned off by turning the the heater off inside the car during hot weather. Then the gas can absorb heat from the engine’s hot water system to vaporise the gas from a liquid, and turn it into a gas without the vapouriser freezing up.

I did try it without any hot water turned on, by turning the thermostat off that I fitted as a “mod”, (mentioned and explained below), but after a few miles the engine stopped because the vapouriser freezes solid, and stops working!

A “mod” I did on my vapouriser was to fit a 12V DC water solenoid in series with the vapouriser, and a “fish tank” thermostat to the vapouriser, so I could keep the vapouriser at “room temperature”. Notice the thermostat strapped to the back of the vapouriser using some “curtain lines” and hooks to hold it in place, (this was what I had handy at the time, I did think of controlling it electronically, and digitally, but as this worked, I said “why not!”, and left it as it was)

Why you may ask did I do this mod?

The reason was to eliminate a flat spot caused when the vapouriser got too hot! Keeping it at a steady temperature in my case seemed to work!

I don’t know why, maybe a wrong mixture at a certain temperature; but it worked, and so I’ll leave it at that!

So a new LPG “run better” “mod” came into being!

The “mixture” is controlled by the manifold vacuum, which cases the diaphragm in the vapouriser to release the correct amount of gas. This is adjustable by various screws on the vapouriser, and by fitting a “restrictor” if required from the vapouriser to the mixer.

From the vapouriser a rubber tube takes the now vapourised gas into the mixer “polo mint” which is inside the air-filter.

The OMVL controller switch incorporates a fuel gauge using the 10K potentiometer from the multi-valve’s fuel gauge arm inside the hatchback boot area, to the controller under the dashboard area.

The switch on the panel switches the solenoid on, and the petrol injector off, or the reverse. When on gas the fuel gauge displays from the float level output signal inside the multi-valve.

When fitting the control switch and fuel indicator, you have to break into the Bosch single point fuel injector’s electrical supply, and divert it through the control relay in the panel so it can be turned off.

A Haynes manual or some common sense should be OK if you are OK on electrics and mechanics, or have someone to advise you.

With multi-rail fuel injection systems you need to turn off all of the injectors, so you are only running on gas.

Some modern EFI systems require you to “fool” your existing EFI system so it thinks it is still running on petrol, so as to avoid a “fault condition”. Further add-ons are available for this.

It is possible to get an “add-on” so you can use your existing lambda probe oxygen sensor to control the fuel supply, and so run the unit “closed loop” after a warm-up period, and thus get more efficiency, and economy.

I chose “open loop”, without using the existing EFI Lambda control, and so kept the cost down, and hassle free fitting on my “basic” car engine, but at a loss in economy and performance.

The second LPG EFI system needs to be set up using a computer, so as to get the correct power curve, and mixture etc. from your vehicle.

Given the choice now, EFI management is the way to go, giving a seamless performance, and no “blips” on the way!

The installation took me one nice day to do, working from eight until six on the evening.

After I had done the tank, piping, and the wiring, I was off to “fill up”

Filling up was by using an adaptor, and screwing it up tight with the clamp-on hand pump dispenser. You need to keep the adaptor handy in the car to fill up as required!

Once hooked up I pulled the trigger and filled it right up for less than half the price of petrol at the time.

So this was it!- a run on LPG!…

I switched over, and it worked OK, except I noticed the power was down, and there was a flat spot at 2500 RPM. We’ll come to this later.

I then took my car to be inspected back in Hereford where I bought the kit, and I passed and got a 10 year certificate to say all was well, which I also passed onto the new owner of the car when I sold it.

The economy wasn’t as good as on petrol, but it was a lot cheaper. I would say 10% worse, but only 40% as much as on petrol, at a guess.

I wish I had gone for an 80 litre tank, as a 40 litre was “OK”, but it wasn’t as big as the petrol tank, and so I had to refill a lot more.

I lived with this for some weeks, until I decided to have a look at the problem.

The problem was down to worn out leads and spark-plugs. It is ESSENTIAL for you to have a tip-top ignition system, or else it will be trouble!

Once this was done it was a lot better, but still had a flat spot; however when I fitted a water thermostat (as mentioned elsewhere) to the multi-valve it cured the problem!

Starting was best on petrol to get it going, and then over onto gas right away. On gas alone it often would not start, as is normal so I am led to understand.

Sometimes on “very big hills” I needed to switch over to petrol to climb them in fourth gear, and then to switch over to LPG once ascended.

After all this I used the car for two years, before selling it because it was getting a bit “old”.

If I had my time over again I would have a new car, and get a grant to convert it over to LPG, and keep it.

That is unless I start making biodiesel!

Having said that; I reckon that is another blog!

Thanks for reading, and if you do this BE SAFE! GET IT CHECKED OUT AND INSPECTED ASAP AFTER FITTING. IF UNSURE ABOUT THE INSTALLATION DO NOT FILL UP WITH LPG! please.

Generally they are safe, but please excercise caution with LPG!

How Does LPG Work?

An LPG Conversion works in exactly the same way as a normal petrol engine, just with a different fuel. Everything about your vehicle remains the same but a separate fuelling system is added with its own tank, piping, ECU and injectors.

Converted vehicles become “dual-fuel” – they can change between running on petrol or gas at the flick of a switch, even whilst driving. As LPG is a much cleaner fuel, there is less wear and tear on the engine and its life will be prolonged. LPG is also 100% lead-free, produces fewer emissions (which is why it attracts a lower duty rate) and causes less oil-contamination. Combustion is cleaner, your engine will be quieter and smoother and much better for the environment.

Earlier LPG systems are renowned for having problems when fitted to modern engines with all of their electronic wizardry. The car would detect that something wasn’t quite right and try and adjust the fuel flow, resulting in backfires, stuttering and occasionally more serious problems.

Thankfully, modern systems are now able to completely interact with most makes of vehicle and you won’t know whether you are running on petrol or gas without looking at the switch.

Also, LPG-converted cars are now starting to rise in residual value as buyers realise that they can run at half the costs of a normal car.

Thanks for reading this, and I hope you have a happy and safe LPG Propane Autogas Conversion soon.

I had a bit of a misfire and a few flat spots, but it seemed to run OK, saving money from the word go, with a short payback time because the kit was so cheap and I installed it myself.

There are more places to fill up with LPG now available, check the link for details.

Now I drive a diesel, which falls “somewhere in between” LPG and petrol I think on economy etc.

See http://www.thereviewbroads.com some more interesting stuff about all sorts of topics.

Mark Lawton

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