Last update:

07/07/2008

  SVI LPG Conv (24V)

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The 24V Cosworth engined Scorpio is a powerful beast but also has a thirst to match. Having owned mine for 2 years and covered around 25,000 miles in that time, I have experienced around 19mpg around town and 25mpg on a fast motorway run. I have to boast that mine has been extremely well looked after with new oil and filters every 5000 miles, new plugs every 10,000 along with a regular MAF and Idle control clean. So it runs well and at 114,000 miles seems ready to go for another 50,000 before needing any work.

But with petrol prices increasing and having made the decision to keep the car (well as the web master I couldn't keep developing the site unless I still owned one!) I decided to invest in an LPG conversion courtesy of Gas Power UK Ltd.

I started doing my homework and looking at conversions done by other Scorpio owners, which were based around an FES Autogas system. This placed an injector at the position of the MAF at the start of the inlet manifold trunking which injected the LPG which was then mixed with air in the inlet manifold and sucked into the cylinders where it is ignited.

Although this system does work, it presents a number of issues that caused me some concern.

  1. It's quite a difficult system to tune across the engine rev/load range
  2. It fills the (plastic) inlet tract with a highly flammable mixture that can ignite and destroy the inlet tracts
  3. There are delays is switching between LPG and Petrol and back again
  4. It is open loop and relies upon electro-mechanical control systems
  5. There are performance issues

Now, don't get me wrong. This is a cheap system to install especially for the home installer and you will recover your purchase costs very quickly. Personally I would recommend it only for the 4 cylinder cars and I have subsequently spoken to LPG installers who have all said that they would not recommend this solution for the 24V - in fact nearly all refuse to even take on a 24V because of it's complexity.

I approached Gas Power UK in Exeter with the 24V and the owner, Steve Fricker, is very approachable and his staff lack the usual 'attitude' of mechanics, being friendly and helpful (they let me have access to the car to spray cavity wax when it was up on the ramp).

After taking a look at the car, Steve acknowledged that it was going to be complex and suggested that the Romano Sequential Vapour Injection system was the only solution that would work effectively.

The SVI system is the latest development in LPG conversions, and uses an injector per cylinder approach that mimics modern multi point fuel injection systems as fitted to the Scorpio. The injectors are fired by an ECU (Computer) based upon an Engine Load map which is learnt by the ECU during setup. The actual fuel injected is refined by the ECU measuring the exhaust mixture through the Lamda sensors, ensuring that the mixture is correct at all times.

Because it injects fuel into the inlet valve for the cylinder, the SVI solution would not be affected by the inlet tract issues of the 24V where the VIS system changes the air dynamics at different engine loads, nor does it fill it with LPG/Air mixture. As the petrol injectors are primed with fuel at all times, switch over between LPG and Petrol is instantaneous without any loss of power.
Performance is said to be identical to petrol and the economy should be only 10% lower with LPG.

Installing the Romano SVI
The system comprises a rear boot mounted LPG tank that is highly damage resistant. I went for the doughnut tank that was to be installed in the spare wheel bay. I have noticed that other vehicles have had the tank installed but that it stood proud of the boot floor and required half of the floor to be at a different height. Gas Power UK took a grinder to the boot, removed a section and welded a new plate in complete with special bolts that are used to retain the tank. It is certainly a neat job as you can see.

The next items to be installed were the injector pipes. These are fitted by removing the inlet manifolds and marking and drilling the manifolds to take brass pipes. The positioning of these are critical to the balance and overall performance of the system and a lot of time was taken ensuring that they were not only symmetrical, but also that the injectors and feed pipes could be located around the reinstalled manifold. New gaskets were ordered and fitted both for the manifolds as well as the O rings used where they join.

Next the two vaporizers were located and installed. The LPG is piped as a liquid to the engine bay through a copper tube where it enters the vaporizer and is turned into a gas. As LPG liquid turns into 250 times it's volume as a gas, it is impossible to inject LPG in liquid form reliably into an engine as the quantity would have to 250 times more accurate than injecting a gas.
Anyone who remembers their GSCE Physics will know that when the liquid turns into a gas it cools down and so to prevent freezing the vaporizer is heated using the engine coolant. This was taken via a T piece installed into the heater pipework. After calculations were made, it was realised that a single vaporizer would be on the limit when feeding the engine under maximum load and so a decision was made to install two, one for each bank. To prevent the injectors from becoming clogged, dual inline filters were added.

Next came the control system. The ECU was installed behind the left hand lamp cover which made for a hidden and very neat install. Electrical connections were made to the coil via a diode pack as the coil on the 24V is actually 3 coils in one. One of the vaporizers was fitted with a coolant temperature sensor and a solenoid valve added to switch off the gas supply when running on Petrol. In order to ensure that the 24Vs EEC-V was not throwing up errors all of the time when running on LPG, an Emulator was installed between the Petrol injectors and the injector leads. When running on LPG this fools the EEC-V into thinking that the petrol injectors are firing normally. An interior switch was added in the area underneath the 2007 Radio fitted to my 95 Scorpio (this can be located wherever convenient). It comprises a Gas/Petrol switch and a 5 LED gauge showing LPG quantity remaining. Finally the wires to the two Lamda sensors were split and a feed to the ECU spliced in in series. This enables the LPG ECU to measure the exhaust mixture and to compensate (trim) as needed.

Finally the entire system was ready for testing and a small amount of LPG was added to the tank and each joint tested for leakage, both statically as well as moving pipes etc to simulate vibration. When each joint was shown to be gas tight the car was started on Petrol and brought up to temperature and then switched over to LPG. Using the Romano diagnostic software, each connection and sensor was tested and the basic map established at idle. We then took the car for a mapping session.

Mapping comprised driving with a set number of styles, ranging from high speed, high load through gentle acceleration and deceleration with a passenger driving the laptop taking measurements. The resultant map was then used to calculate the full range of fuel/load maps that are used by the ECU to inject LPG and which are then trimmed by the information from the Lamda sensors.

I then took the car for an 850 mile round trip to Scotland for the weekend to identify any problems.

Driving impressions
Firstly I have to say that I am absolutely amazed by the quality of installation and the drivability of the car. Full acceleration seems smoother on LPG and there is no hesitation when switching between LPG and Petrol. I have noticed that coolant temperature is critical to running on LPG and I have requested that the initial temperature when LPG starts to be used be raised by 10 degrees to 35 degrees to prevent stalling on cold mornings.

I believe that the improved smoothness is a result of gas being injected rather than a liquid being injected which is the atomised by the injector. As my vehicle has done 114k miles, the petrol injectors must be quite dirty (despite regular injector cleaner) and their atomisation is probably less than perfect. However when injecting LPG it is all gas and so the flame front within the cylinder must be better - result is smoother running and in particular, smoother acceleration.

 

What a new petrol injector should do. What mine probably do after 114k miles.

This is a clear example of why LPG provides a smoother burn - this shows a typical fuel injector spray complete with fuel droplets.

Fuel economy was very impressive too - on short journeys I have been getting 19 on Petrol but over the weekend I was seeing 22 on LPG (although the first mile is still run on Petrol which will affect the readings). On fast motorway routes (based over 800 miles of motorway) I saw an overall consumption of 24mpg (25 on petrol) and that included 2 hours stuck on the M6 at Birmingham. I really did not expect that sort of economy.

The only problem so far is that the fuel gauge (the 5 LEDs) is very pessimistic, showing empty after just 140 miles whereas with a 12 gallon capacity it is capable of at least 240 miles - I am just a little concerned about running out of LPG as with an automatic it is a somewhat fraught experience when the engine stops and you have to restart it whilst still driving :)

Overall
OK, the 24V is a complex conversion and the Romano solution is not cheap. However if you plan on keeping your vehicle, do 12,000 miles a year or more and want to do your bit to help save the environment then I can seriously recommend Gas Power UK and their conversion. They can convert the car in approx 5 days and if anyone want to see and try mine before designing then I am quite willing to demonstrate down here in Exeter.

Final conversion price including VAT and a full tank of LPG is 1900

Contacts:
Gas Power UK Ltd - 01392 879 290  (Stephen.Fricker@Gaspower-uk.com)

 

Photo Gallery (click to enlarge)

Dropping the fuel tank to cut the bottom of the spare wheel well to install the doughnut tank
Tank installed showing the virtually flat boot floor
With the rear carpet down you would not know there was a tank underneath. Meets my wife's requirement that it would not take up valuable boot space.
The new LPG filler installed
Dismantling the inlet manifolds to drill and tap them for new LPG injectors.
The engine in it's dismantled state. New gaskets and O rings were fitted as a matter of course.
Drilling and tapping the manifolds
Note the accurate positions of the injection pipes, keeping them as symmetrical as possible to ensure an even injection of LPG across all six cylinders.
Installing the emulator loom onto the petrol injectors
Installing the twin vaporisers - one with a coolant temperature sensor and mounted above the exhaust manifold to keep them nice and hot.
Installing twin inline filters to ensure that the injectors stay clean
Wiring up the system
Final manifold installation
Interior fuel selection switch with LPG gauge
Final finishing (annotated diagram)
The finished article. The only remaining job is to modify the engine cover to fit back onto the engine
 

 

The components of the Romano SVI System

 
The ECU Vaporiser Fuel Filter Injector
   
Solenoid Valve   Emulator  

 

 

 

 

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