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Part 3 - LPG Conversion Installation

<< Part 2 - LPG Kit | LPG Conversion Index | Part 4 - Setup >>

The installation here was done in accordance with the LPGA Code of practice COP11 and the instructions that were included in the kit for the components and the electrical connections. The manufacturer instructions were complemented by the instructions written and supplied by Tinleytech. The project was completed over several weekends with the car being roadworthy for all but one day where the manifold needed removing/refitting.

Locating The Components

After receiving the kit a start was made in deciding the location of each component. As you may be aware the engine bay of a turbocharged Impreza leaves little room for additional fittings.

The Vaporiser

The initial thoughts were that the vaporiser unit would be mounted on the OS inner wing. This proved to be problematic as the LPG gas line would run too close to the exhaust system. The wiring for the ECU would also have to be routed to this location, again proving problematic due to most of the connections needing to go the the petrol ECU and battery, both of which are located on the NS inner wing/bulkhead area.

A test was conducted to see what room would be available IF the washer bottle was removed from the under bonnet area. This is shown in the photos below.

The vaporiser unit fits in nicely and there is still space for the shut off valve that receives the gas line from the tank. The washer bottle would need relocating to the boot. This is shown later.


The location for the ECU needs to be free from sources of heat and water. I initially thought about having the ECU inside the cabin but the routing of the loom, with its large connector plugs, through the bulkhead was a problem without cutting large holes. I finally decided that the ECU could be located on a bracket just under the air-con cleaner unit on the chassis rail. This would mean the minimum amount of wiring to route through to the petrol ECU.

ScoobyLPG-EcuLocation.jpg: 640x480, 289k (March 29, 2014, at 09:42 PM)
ScoobyLPG-ECUPrefit.jpg: 640x480, 336k (March 29, 2014, at 09:42 PM)
ScoobyLPG-WiringLoom.jpg: 480x640, 338k (August 28, 2009, at 10:11 PM)

The Tank

The tank I had bought had already been specified according to the boot space available. I didn't want a tank that fitted in the wheel well as these had limited capacity. You can only fill the tank to 80% of it's capacity due to thermal expansion. So an 80lt cylindrical tank was bought. It measures 360 mm x 892 mm and is fairly heavy, although I never weighed it. I stripped the boot space to see where it would fit.

ScoobyLPG-TankPic.jpg: 306x243, 10k (August 28, 2009, at 10:12 PM)

The Injectors

The injectors were delivered after the rest of the kit. They were a special order from BiGas Italay as I needed the 3.3mm size in order to flow enough gas on boost and I never got a chance to see where they would fit until the actual fitting.

ScoobyLPG-Injectors1.jpg: 640x480, 261k (August 28, 2009, at 10:16 PM)
ScoobyLPG-Injectors2.jpg: 640x480, 322k (August 28, 2009, at 10:16 PM)
ScoobyLPG-Injectors.jpg: 640x480, 287k (August 28, 2009, at 10:16 PM)

The Filler

I was never intending to fit the filler where it would be visible so a suggestion was made by the old man to mount it behind the number plate. A quick checked showed that there was very little room behind the bumper and that I would need a 90degree filler. This was supplied by Tinleytech.

The rest of the kit would simply be fitted as a "best fit" as we couldn't envisage problems that we couldn't work around.

The Fitment Of The Kit.

After finding and testing the locations for the various large components it was time to start the install. The details below also show the order in which the components were fitted.

Tank And Filler

I started at the rear of the car with the tank and filler mechanism. The tank cradle was placed in the boot space and moved around to find the best location. The Impreza has access panels to the fuel pump and sender unit that still need to be available. Moving the cradle forward of these allowed it to sit level but created a couple of problems. The frame wasn't wide enough to sit on the chassis rails and was over the spare wheel well eliminating the possibility of keeping a spare wheel in the car. For the last 4 years of ownership I had never had the spare wheel in the boot anyway so it was decided to lose the spare wheel altogether. This would allow space for the washer bottle relocation and for fabricating extra mounting points for the tank frame. The code of practice states that for my size of tank and the type of frame being used 4 mounting points should be used. The pictures below detail the process including showing the extra framework fabricated to make the frame fit. I also welded in some captive plates/bolts to hold the rear of the frame as this sits directly over the rear cross member. Spreader plates are used under the car as per the code of practice.

ScoobyLPG-BootPreFit.jpg: 640x480, 348k (March 29, 2014, at 09:41 PM)
ScoobyLPG-CaptiveMounts.jpg: 640x480, 413k (March 29, 2014, at 09:41 PM)
ScoobyLPG-CaptiveMounts2.jpg: 640x480, 309k (March 29, 2014, at 09:41 PM)
ScoobyLPG-CaptiveMounts3.jpg: 640x480, 335k (March 29, 2014, at 09:41 PM)
ScoobyLPG-TankFrame.jpg: 640x480, 378k (August 28, 2009, at 10:13 PM)
ScoobyLPG-TankFrame1.jpg: 640x480, 321k (August 28, 2009, at 10:13 PM)
ScoobyLPG-TankFrameBoot.jpg: 640x480, 340k (August 28, 2009, at 10:12 PM)
ScoobyLPG-TankFrameBoot1.jpg: 640x480, 355k (August 28, 2009, at 10:12 PM)
ScoobyLPG-TankFrameBoot2.jpg: 640x480, 349k (August 28, 2009, at 10:12 PM)
ScoobyLPG-TankFrameFitted.jpg: 640x480, 308k (August 28, 2009, at 10:12 PM)
ScoobyLPG-TankBracket1.jpg: 640x480, 337k (August 28, 2009, at 10:13 PM)
ScoobyLPG-TankBracketUnder1.jpg: 640x480, 326k (August 28, 2009, at 10:13 PM)

The tank was then positioned and fastened down using the straps supplied. The multivalve, gastight box and vent tubes were fitted and secured. The multivalve has the filler valve, fuel level sensor, tank solenoid valve and emergency vent valve all merged into one device. The gastight box allows the venting of gas in the event of a leak, through the vent tubes and then outside of the vehicle. All gas pipes and wiring are routed through the vent tubes. The washer bottles are shown with the right hand side feeding the rear and the other feeding the front.

The tank is mounted with the filler hole at 30 degrees to the vertical. This allows the correct fitment and operation of the level sensor and filler valve which automatically stops the filling process at 80% full. If the tank isn't mounted correctly the mechanism can allow overfilling of the tank.

ScoobyLPG-TankFinished.jpg: 640x480, 316k (August 28, 2009, at 10:13 PM)
ScoobyLPG-TankFinished1.jpg: 640x480, 307k (August 28, 2009, at 10:13 PM)
ScoobyLPG-TankFinished2.jpg: 640x480, 332k (August 28, 2009, at 10:13 PM)
ScoobyLPG-GasTightBox.jpg: 640x480, 307k (August 28, 2009, at 10:16 PM)
ScoobyLPG-WasherBottles.jpg: 640x480, 343k (August 28, 2009, at 10:11 PM)
ScoobyLPG-SenderUnit.jpg: 640x480, 409k (August 28, 2009, at 10:14 PM)
ScoobyLPG-SingleHoleTank.jpg: 640x480, 246k (August 28, 2009, at 10:14 PM)
ScoobyLPG-SingleHoleTank1.jpg: 640x480, 292k (August 28, 2009, at 10:14 PM)
ScoobyLPG-SingleHoleTank2.jpg: 640x480, 301k (August 28, 2009, at 10:13 PM)

The filler mechanism and cap were located behind a hinged number plate. The hole was first marked out and then cut by drilling small holes all the way round before being filed. I didn't have a hole saw of the right size and this method worked nicely. The unit is fitted in place using 6 screws and a plastic cap on the rear of the filler. The 8mm flexi pipe from the filler runs behind the bumper and then into the vent tube before reaching the gastight box and multivalve.

The code of practice states that the pipelines and filler need to be at least 250mm away from exhaust components. Having the filler fitted at this side no only satisfies this but also keeps both LPG and Petrol fillers at the same side of the car.

ScoobyLPG-FillerAndPlate.jpg: 640x480, 374k (March 29, 2014, at 09:43 PM)
ScoobyLPG-FillerLocation1.jpg: 640x480, 339k (March 29, 2014, at 09:43 PM)
ScoobyLPG-PlateHinges1.jpg: 640x480, 344k (August 28, 2009, at 10:14 PM)
ScoobyLPG-FillerAndPlate1.jpg: 640x480, 334k (March 29, 2014, at 09:43 PM)
ScoobyLPG-PlateHinges.jpg: 640x480, 301k (August 28, 2009, at 10:14 PM)
ScoobyLPG-FillerPipe2.jpg: 640x480, 359k (March 29, 2014, at 09:43 PM)

The Vaporiser

This was probably the most difficult part to fit. A bracket had been supplied with the kit that is used to mount the vaporiser but this wasn't suitable for the location I had in mind. The washer bottle had now been removed from the inner wing so the space was available for the unit although it still needed to be mounted in a way that would allow for all of it's connections. The unit would have a liquid LPG supply, 2 coolant hoses running from the car, 2 gas outlet pipes for the injectors, 2 vacuum/pressure pipes and the electrical connection for the temp sensor. The only way forward was to develop a new bracket that could be used to mount the vaporiser. During this process it was decided that the shut off valve that goes between the LPG pipe and vaporiser would in some way be mounted on the same bracket. The connecting pipe between the shut off valve and the vaporiser is the only one that is made from copper. The copper pipe was used as the fixings at either end are shorter than those for the flexi pipe.

As it happened, the holes left by removing the washer bottle plus the fuel filter mounts could be used for mounting the bracket, thus avoiding drilling news holes.

ScoobyLPG-BracketMoun2.jpg: 640x480, 332k (March 29, 2014, at 09:41 PM)
ScoobyLPG-BracketMoun4.jpg: 640x480, 312k (March 29, 2014, at 09:41 PM)
ScoobyLPG-BracketMount1.jpg: 640x480, 313k (March 29, 2014, at 09:41 PM)
ScoobyLPG-VapouriserInCar1.jpg: 640x480, 380k (August 28, 2009, at 10:12 PM)
ScoobyLPG-VapouriserInCar2.jpg: 640x480, 379k (August 28, 2009, at 10:12 PM)

The next step was to connect the coolant hoses from the cars heating system. The vaporiser needs these feeds in order to stop the liquid LPG from freezing when it turns to gas. This was a simple case of removing the intercooler and making the connections shown.

ScoobyLPG-CoolantConnections.jpg: 640x480, 355k (March 29, 2014, at 09:42 PM)
ScoobyLPG-CoolantVaporiser.jpg: 640x480, 375k (March 29, 2014, at 09:42 PM)

LPG Fuel Line - Tank To Vaporiser

The routing of the pipeline was first attempted using the 8mm copper pipe that was originally supplied with the kit. I attempted to route the pipe out of the spare wheel well and then between the floor pan and rear cross member and then down the NS of the car to the vaporiser. At best this was an exercise in skin removal and was aborted within an hour or so. After obtaining some 8mm flexi pipe from Tinleytech I routed the pipe (as shown in the pics) down the NS of the car. I used some rubber heater hose to protect the pipe where it was routed through the cross member and some rubber grommets for where it passes through the 2 holes I drilled in the front chassis rail. Where the pipe enters the engine bay I have used cable ties to fasten the pipe to the air-con pipes before reaching the shut off valve and vaporiser.

ScoobyLPG-LPGpipe.jpg: 480x640, 299k (August 28, 2009, at 10:16 PM)
ScoobyLPG-LPGpipeTube.jpg: 640x480, 321k (August 28, 2009, at 10:15 PM)
Rear Sub frame Mount
ScoobyLPG-PipeThroughChassis.jpg: 640x480, 286k (August 28, 2009, at 10:14 PM)
Front Chassis Rail

Injector Nozzles And Manifold

The fitment of the injector nozzles in the manifold was the only operation that required the car to be off the road. The inlet manifold was removed from the car and took about an hour or so.

With the manifold off the holes can be drilled using a 5mm drill bit ready for tapping with a 6mm tap. The holes ideally should be at 45 degrees to the runner in the direction of airflow and within 5cm of the original petrol injectors. A test was carried out on a piece of aluminium plate of the same thickness as the walls of the manifold to see how the drilling (by hand) would work. 45 degrees resulted in the nozzle not protruding into the plate far enough so a compromise was found that allowed a reasonable angle and the nozzle to be far enough through.

The pictures show the drilling and positioning for the nozzles. A small section of the manifold just above each nozzle was machined to allow the nozzle to screw in further. At the time of fitting the nozzles the injector for the flashlube system was installed in the throttle body just behind the butterfly.

ScoobyLPG-Manifold2.jpg: 640x480, 345k (August 28, 2009, at 10:15 PM)
ScoobyLPG-Manifold3.jpg: 640x480, 387k (August 28, 2009, at 10:15 PM)
ScoobyLPG-Manifold4.jpg: 640x480, 344k (August 28, 2009, at 10:15 PM)
ScoobyLPG-Manifold7.jpg: 640x480, 294k (August 28, 2009, at 10:15 PM)
ScoobyLPG-FlashlubeNozzle.jpg: 640x480, 316k (August 28, 2009, at 10:16 PM)

Battery Replacement

After fitting the vaporiser it was clear that the original Subaru battery would interfere with the gas pipes leading to the injectors. An attempt was made to route the gas pipes around the battery although the bends were too tight and this idea was discarded. This was a consideration when first thinking about the location for the vaporiser.

A new battery was sourced from a local supplier. This was an 015 Varta that is the same size as the one fitted to the Subaru Justy. A bracket was fabricated to hold the battery in place along with a bracket to hold the gas filters. The terminals of the new battery were the smaller type and needed adapters to allow the existing leads to be connected, which were only just long enough.

The car starts fine on the smaller battery and as I do 50 miles per day, keeping it charged should be ok.

ScoobyLPG-BatteryFitted.jpg: 640x480, 397k (March 29, 2014, at 09:40 PM)
ScoobyLPG-FilterBracket.jpg: 640x480, 334k (August 28, 2009, at 10:16 PM)

Gas Pipes, Filters And Injectors

The 2 gas pipes from the vaporiser come from essentially separate units and need balancing to ensure the correct gas pressure to both injector banks. This is even more important due to the fact that the OS injectors have nearly twice the length of gas hose to the NS injectors. The H section balance piece was sourced from my local air tools outlet.

The H section then feeds into 2 filters, one for each bank of injectors, and then out to the injectors. The injectors are mounted on fabricated brackets that fasten to the manifold via rubber mounts. The long section of gas hose that feeds the OS bank is fastened to the power steering fluid pipe that runs along the top of the radiator fan shroud.

ScoobyLPG-NSinj.jpg: 640x480, 374k (August 28, 2009, at 10:14 PM)
ScoobyLPG-OSinj.jpg: 640x480, 342k (August 28, 2009, at 10:14 PM)
ScoobyLPG-NSInjectors.jpg: 640x480, 383k (August 28, 2009, at 10:15 PM)

Vacuum Lines and MAP Sensor

The vacuum lines run from the manifold through a T piece to the MAP sensor and the Vaporiser (2 connections). The MAP sensor also has a line that runs from one bank of injectors in order to monitor the gas pressure.

ScoobyLPG-MAPSensor.jpg: 640x480, 357k (August 28, 2009, at 10:15 PM)
ScoobyLPG-PressureSensor1.jpg: 640x480, 267k (August 28, 2009, at 10:14 PM)
ScoobyLPG-PressureSensor2.jpg: 640x480, 294k (August 28, 2009, at 10:14 PM)
ScoobyLPG-PressureSensor.jpg: 640x480, 256k (August 28, 2009, at 10:16 PM)

ECU And Wiring Harness

The ECU was mounted using an L shaped bracket bolted to the chassis member. They only way I could get it to fit was to mount it horizontally rather than with the wiring loom facing downwards as suggested. It should be protected from water ingress and the seals seem pretty good.

The wiring loom I used for the injectors required cutting the original injector loom and soldering the connections needed. The alternative is to purchase a loom that connects to the original injector plugs and in doing so eliminates the cutting of any wires. Tracing the original wiring was fairly easy so this was an easy saving to make.

The gas injectors have there own loom that I shortened to remove the unnecessary length.

The wiring connections were as follows:

  • Connection from the gas ECU to the RPM and Lambda of the Petrol ECU.
  • Connections to the Vaporiser and Injector temp sensors.
  • Connections to the Positive and Negative terminals of the battery.
  • Connections to the Vaporiser and Tank shut off valves.
  • Connection to the Tank Fuel Level sensor.
  • Connections to each of the 4 Injector negative feeds. This part breaks the original loom to allow the gas ECU to take control of the signal.
  • Connection to the MAP sensor of the gas ECU.
  • Connection to the 2 banks of gas injectors.
ScoobyLPG-ECUFitted.jpg: 640x480, 388k (March 29, 2014, at 09:42 PM)
ScoobyLPG-ECUbracket.jpg: 640x480, 380k (March 29, 2014, at 09:42 PM)
ScoobyLPG-LoomCut.jpg: 640x480, 358k (August 28, 2009, at 10:15 PM)

Interior Change Over Switch

The change over switch was mounted on the centre console just behind the gearlever. This proved difficult to view while on the move so it was moved to the dashboard as shown. The wiring loom passes through the bulkhead and simply plugs into the rear of the switch.

ScoobyLPG-Changeover1.jpg: 640x480, 307k (March 29, 2014, at 09:41 PM)
ScoobyLPG-Changeover2.jpg: 640x480, 321k (March 29, 2014, at 09:41 PM)
ScoobyLPG-DashBoard.jpg: 640x480, 275k (March 29, 2014, at 09:42 PM)

The Finished Engine Bay

This is the finished engine bay showing the flashlube system on the OS wing.

ScoobyLPG-UnderBonnetLPG1.jpg: 640x480, 412k (August 28, 2009, at 10:12 PM)

Information Source - ScoobyLPG website, republished with permission,

<< Part 2 - LPG Kit | LPG Conversion Index | Part 4 - Setup >>

Page last modified on June 13, 2008, at 05:08 PM
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