Fitting A DIY LPG Conversion Kit To A Vehicle

May 20 2010

Fitting A DIY LPG Conversion Kit To A Vehicle

Category: Fitting A DIY LPG Conversion Kit To A Vehicle,Motoring — Mark Lawton @ 9:27 PM

Fitting A DIY LPG Conversion Kit To A Vehicle

This is about how I bought a DIY LPG conversion kit, and I converted my car to run on LPG, or Liquid Petroleum Gas (Propane). The DIY LPG kit cost about £350.00 in the year 2000, which even then was very good value. With the DIY LPG Conversion kit I got the PVC coated LPG rated copper tube, the Liquid LPG vaporizer and LPG reducer, an LPG safety solenoid, the 40L cylindrical LPG tank, the LPG air mixer, and the LPG/petrol changeover switch and LPG controller unit. Included in the kit was the LPG multi-valve with a mechanical LPG fuel gauge, and the electronic LPG fuel gauge included in the LPG control panel, which is right next to the LPG/Petrol changeover switch mounted under the dashboard.

Typical OMVL Parts required for a DIY Propane LPG Conversion

Typical OMVL Parts required for a DIY LPG Conversion

Don’t forget to go back for the inspection and certificate, and to notify the DVLA on the V5 about the new LPG fuel. Also don’t forget to notify your insurance about the LPG conversion. You may be OK with your current insurer, or you may need to change to a broker who has no “hang-ups” about LPG. It is perfectly safe if LPG is installed by a competent DIY person, or recognised LPG fitter. LPG will not explode any more than petrol will, in fact in open air if the LPGpropane gas escapes un-ignited and disperses, then the danger is less. With the LPG inspection and 10 year certificate, you can insure and sell your vehicle with no problems, and greener people welcome the change to LPG, and are quite excited to buy an LPG converted vehicle, and run around on LPG saving 40-45 % plus on fuel bills!

There may be certain restrictions on some tunnels in the UK. (check the web for details)

Remember the tanks are very tough, way tougher than a petrol tank, which is made of very thin material, LPG tanks are built to withstand high impacts which may only dent them, and they are tested to over 600 PSI (pounds per square inch). LPG is up to 200 PSI inside the tank.

It is often branded as Autogas, but LPG is generally about 80 to 90% as economical a petroleum (approx average guess in my case), but only half the price of petrol.

As a hobby, or a bit of an experiment, I decided to do an LPG conversionto my Skoda Favorit, using an OMVL (O.M.V.L) kit to convert my car to run on LPG, which could also be switched back to petrol at the flick of a switch.

After some searching online, and making a few phone calls, I decided to set off to Hereford for my LPG conversion kit, to carry out a full DIY LPG conversion.

The parts are Italian, and made by OMVL (O.M.V.L). The people there were very helpful, and offered me a free inspection and certificate upon my return, after I had finished the installation at home first at my leisure.

I will now describe the process, and also supply some illustrations. I fitted the LPG conversion kit in one day working for about 8 hours, and on a rare sunny day at that!

You may need this too… http://mark-lawton.com/wp-content/uploads/2010/07/Zeus-Tables-Reduced-Size.pdf

(These are tables for looking up screwthreads etc.)

I will describe the parts, and what they do…

First there is the LPG tank, this can be fitted in the boot, or in the spare wheel well. The tank is bracketed into place securely to the bodywork of the car.

I chose a 40 Litre LPG tank, and I could get about 100 to 150 miles out of this tank, depending upon the settings, and the driving conditions. Notice the strapping to keep it still when driving.

The tank looked like this in the back; ignore the other box on some pictures shown later, that is a sub-woofer! lol

LPG Tank Side View

The tank incorporates the fuel gauge assembly, and the safety valve. The copper pipe carries liquid gas from the tank, underneath the car following the brake pipes underneath into the engine compartment. (Notice the thumb-screws to turn off the fuel, and the inlet for filling)

LPG Multi-Valve With Lid Removed

LPG Multi-Valve Assembly With Lid On

A second pipe goes to the filling point on the back of the tow-bar. The complete LPG kit had most of the bits that I needed, including all the brackets for the tank and fuel pipes, which are also covered in PVC to protect them.

LPG Filling Point on Towbar

It is important to fit the LPG kit exactly to the instructions, and get no leaks, or chafed pipes.

Avoid sharp corners, and too tight a bend with the copper pipework. Remove swarf after cutting any pipes, and ensure none has gone inside the pipework. notice the LPG pipework below.

LPG Pipes Under Car Following Brake Lines etc.

The refilling point it on the tow-bar, and an adaptor is supplied with the kit to enable you to refill at most LPG garages. The adaptor enable you to refuel at many different garages who may have different types of coupling, but most now are fairly standard.

LPG Refueling Adaptors Various

LPG Refueling Point Shown Open

The fuel indicator is mechanical in the boot with a needle, however I also had the fuel selector with a fuel gauge as well. The accuracy is a bit dubious, because the tank is round the fuel level drops at different rates, and so it is fast, slow, and then fast again due to the curvature of the tank causing the level differences as you drive.

Notice the two thumbscrews below on the Multi-Valve; you can turn off the gas and the inlet pipe (shown earlier), so that the tank can be isolated and removed if ther is a need. The Multi-Valve allows refilling, and also shows the fuel level mechanically, besides having a potentiometer (variable resistor) output to display the fuel level in a dashboard mounted fuel gauge, which is incorporated in the LPG switch/control shown mounted inside the car under the dashboard.

When fitting the control unit inside the car, I fitted it in the centre below the dashboard.

LPG Switch and Fuel Gauge

You need to disconnect the fuel injector on the inlet manifold, and wire it via the relay in the controller. The Skoda had a Bosch single point fuel injector, and no clever failure codes when this is removed, so I was OK to just disconnect it, and wire it through the relay so that no petrol would be used when I switched the car over to gas.

Consult a good Haynes Manual, or someone who knows about the electrics to deal with the fuel injector. Some vehicles will need a way to “fool” the ECU into thinking the injectors are still running, or otherwise their ECU may throw up an error and stop the system from working. In the Skoda with the Bosch single point injector there was no need to do this, and it was straightforward.

Skoda Favorit Haynes Manual

Notice the fuel gauge on the above pic of the LPG Controller changeover switch.

Under the hood the LPGfuel line comes up to the big gas valve, or the vaporizer. This valve has some heater hose connected to it, via the engine’s water cooling system, and it evaporates the LPGinto a liquid inside the vaporizer unit. You need to take a heater hose (before the dashboard heater valve switch obviously so it stays on all the time), and run this through the vaporizer valve. Liquid gas is supplied right up to the vaporizer valve, because if it was a gas from the rear tank, there would not be enough throughput of gas, and the engine would be starved of fuel.

LPG Vaporiser Valve Unit

This valve not only vaporises the fuel, but it also has a diaphragm, and the mixture is set up on it. The inlet manifold vacuum draws the gas from this, and the rate of flow is set up on the valve.

A safety solenoid shuts off the gas before this valve unit, and there is also a solenoid on the valve as well (double safety). When you switch the car’s ignition off, or switch back to petrol, thes solenoid cuts off the gas supply.

LPG Safety Cut-off Solenoid

Next a rubber pipe comes from this into the air filter box, right over the inlet manifold, this is like a giant polo mint with holes in it. This allows the gas to mix with the air. this is fitted right over the air intake venturi. I didn’t take a picture of this, but imagine this inside your air filter right over the intake and you are right on what this would look like

LPG Mixers 3 Different Fitments and Sizes Examples

One thing to remember… start the car on petrol every time first, and then once under way switch it over to LPG. I could switch over as soon as I was on the first decent long road, or a few hundred yards from home.

When you accelerate this vacuum in the inlet manifold draws gas through the mixer, this then mixes with the air, and is taken into the combustion chamber the same as petrol/air, and then normal combustion can take place.

The mixture is further controlled by a restrictor screw in the inlet pipe to the manifold, this can lean or richen the mixture.

LPG Vaposiser Complete (OMVL)

Obviously this system is very basic, and it bypasses the ECU and runs “open loop”, in that there is no feedback and control of the mixture. It does not use the ECU or the oxygen sensor in the exhaust manifold.

Lambda Probe Oxygen Sensor Example

It was a little lumpy at times, but with a bit of tweaking, and the addition of a thermostat for the vaporizer (modified fish tank thermostat and a water valve), I managed to get the car running near perfect on LPG. I had the idea that the valve was getting too hot; so I decided to fit a thermostatic control of the water flow to keep the temperature of it to maybe about 45 degrees C. If it got too hot then too much gas was passing, and the car was then running rich and lumpy.

An addition to finish the job would be the “Leonardo” ECU kit…

Leonardo LPG ECU Mixture Regulation

That would be one example of how to smooth out the flat spots, and improve the economy.

As for the economy with my “open loop” setup… about a 40-45% saving over petrol, and the engine oil after 8000 miles was still clear, showing this is a clean and low emission way to get from A to B.

Where I would knock the system, is the fiddly filling up with the adaptor takes a bit longer than petrol, making sure you know who sells the LPG (a lot now, so not as bad to find), and the accuracy of the fuel gauge is a bit off due to the shape of the tank.

The fitting is straightforward if you are mechanical, and electrical in nature and ability, and you don’t mind taking a drill to your car and doing a few mods.

It is essential to have good spark-plugs, leads, distributor cap, and rotor arm. I found out how bad mine were, as the car was also misfiring, but replacing these did the trick!

These days I would recommend a closed-loop system, utilising your existing oxygen sensor, and an ECU to be fitted. This will need to be mapped out on a computer to get the fuel ratios correct all through the rev-range of the vehicle, and getting the efficiency up to maybe 90-95% as good as running on petrol. Maybe not exactly a DIY project there, but you could always fit it, and get a garage to set it up for you. Please see the above pic for the “Leonardo” ECU setup.

As I say it is half of the cost of petrol to buy, but you don’t get twice the MPG, but it is worth it on large petrol cars. Small diesels aren’t worth converting, but they do use the system on some buses I have noticed. However they have to have the compression reduced, engine parts changed to do this, and a spark-plug ignition system has to be added. The engine also revs higher, and is no longer a diesel. Not a viable option except on maybe buses.

If you would like to read more details, and where I may “fill in the gaps” a bit more, then please read this article…

http://mark-lawton.com/diy-lpg-conversion-kit-fitted-to-a-skoda/

Thanks for reading this,

Here are the rest of the pictures to “fill in the gaps” and illustrate the whole thing a little better…

: LPG Tank Side View

: LPG Multi-Valve With Lid Removed

: LPG Filling Point on Towbar

: LPG Pipes Under Car Following Brake Lines etc.

: LPG Refueling Point Shown Open

: LPG Refueling Adaptors Various

: LPG Multi-Valve Assembly With Lid On

: LPG Switch and Fuel Gauge

: LPG Vaporizer Valve Unit

: LPG Safety Cut-off Solenoid

: LPG Mixers 3 Different Fitments and Sizes Examples

: LPG Vaporizer Complete (OMVL)

: Lambda Probe Oxygen Sensor Example

: Leonardo LPG ECU Mixture Regulation

: LPG Vaporizer Water Thermostat

: Skoda Favorit Haynes Manual

Mark Lawton

Tags: autogas, car lpg, cars lpg, conversions gas, diy lpg, DIY LPG Conversion, DIY lpg kit, gas, gas conversion, gas conversions, leonardo, lpg, lpg cars, lpg controller, lpg conversion, lpg conversion kit, lpg conversions, lpg kit, lpg mixer, lpg reducer, lpg solenoid, lpg tank, OMVL, propane