VT Commodore LPG installation utilising an LPG …

1 VT Commodore LPG installation utilisingan LPG Memcal and Apexus of components and operationLPG/Petrol Changeover switchThe LPG change-over switch is mounted inthe instrument facia to the left of theinstrument cluster and below the tripcomputer controls (Fig. 1). The switch ispush button and has a momentary LPG is selected the green LPGindicator on the instrument cluster isilluminated and a green indicator lights onthe switch. If the push button switch isactivated again the LPG function is turnedoff and the vehicle reverts to petroloperation.

2 Switching between Petrol and LPG operation can only occur while thevehicle is stationary or moving at less than3 kilometres per hour. Each time the fuel mode switch is pushed the vehicle changesfrom one fuel to the other. Even when the ignition is turned off the last fuel in use isremembered by the vehicle computer system and this is the fuel mode it uses thenext time the engine is operationWhen the LPG indicator on the instrument cluster is not visible and the indicator inthe button of the fuel mode switch is OFF the vehicle is running on petrol.

3 In thismode the LPG system is turned OFF and the vehicle functions in the same way asa vehicle not fitted with LPG. When operating on Petrol the fuel gauge shows theamount of petrol in the petrol operationWhen the green indicator (Fig. 2) is lit themode switch has been cycled to LPGoperation. In this mode the PCM (PowerTrain Control Module) activates the LPGmixture control computer and varioussolenoid valves to allow the flow of LPG tothe engine. If the vehicle is fitted withtraction control the PCM will disable thetraction control when LPG is selected.

4 The TRAC OFF traction control indicator inthe instrument cluster will light to indicatethis. In LPG mode the fuel gauge reads theamount of LPG in the LPG tank. Becausethe LPG system uses small amounts ofFig. 1 : Apexus PS122 Gas/Petrol ModeSwitchFig. 2 : Dash fuel gauge used for both LPGand Petrol. LPG lamp shown illuminatedPage 2 of13petrol to start the engine and when running on high power, it is essential to maintainsome fuel in the petrol tank. If the petrol tank is low even in LPG mode the low lampwill light and the digital display will warn Lo Petrol just after engine Pulse widthIn all LPG operating modes, exceptduring cranking and high poweroperation, the petrol injector pulse widthis set to zero.

5 The PCM also injectspetrol during engine cranking to assiststarting. The amount of petrol deliveredduring the start is determined by thecoolant temperature and the crank time(Fig. 3). After cranking no further petrolis delivered to the engine unless it isneeded to cool the valves and stopvalve recession during high speed andhigh power PumpThe petrol pump relay operates thepetrol pump for about two secondswhen the ignition switch is first turnedon, and continues to operate duringcranking and then for about 5 secondsafter the engine has started (Fig.)

6 4).During normal LPG operation the petrolpump is not running unless engaged bythe PCM during high power operation toprevent valve Timing MapA special Electronic Spark Timing (EST)map which has been programmed toprovide optimum timing for LPGoperation is built into the Memcal PROM. Should the engine speed drop below 300 RPM the spark plugs are prevented from firing to reduce the risk of backfire in the airintake ComputerThe PCM fuel usage output signal has a modified calibration to better suit LPG InhibitDuring starting in the LPG mode the PCM prevents the engine from cranking bydeactivating the start inhibit relay if the throttle is opened more than 7%.

7 2 SecCrank5 4 : Petrol Pump OperationIgnitionon secno startInjectorPulseEngine StartPulse time varieswith coolanttemperatureNo further PetrolPulse Whenrunning On LPGTimeFig. 3 : Petrol Injector Pulses for LPG start sequencePage 3 of13 MemcalThe Memcal (Fig. 5) is a PROM(Programmable Read Only Memory).Contained within the LPG Memcal is aprogram so that the PCM can operate inone of two modes, either Petrol or LPG ,ie both the petrol mode and LPG mode areprogrammed into one Memcal so that it isnot necessary to physically change theMemcal to swap from one fuel to the program mode the PCM isoperating in is determined by cycling theLPG changeover switch.

8 The last switchposition being retained in the PCMmemory even when the ignition switch isturned InstallationMechanical InstallationFit tank, LPG lines, converter, mixer, waterlines, vapour line, vapour control valve,filler system, lock-offs, intake manifoldbalance line and any other hardwarerequired for the particular installation (Fig 6.).Electrical InstallationPreparation before fitting the PCM by disconnecting thebattery, removing the left hand front sillcover using a Torx tool, (refer to Fig.)

9 7),and removing the left hand front foot upperpanel. Remove left hand front kick panel(Fig. 8)Fig. 7 : Undoing torx screws holdingsill trimFig. 8 : Undoing kick panel screwFig. 5 : Memcal fitted to PCMM emcalFig. 6 : Vapouriser, lock-off, andApexus electronic safety cut-out (ModelCO100) which provides short circuitand overload protection, withoutblowing the fuseSafetyCut-OutPage 4 of13 The PCM (Fig. 9) is removed by unclippingit from the left hand front of console and facia panel iscarried out by first removing the rubber matfrom below the ash tray and then removingthe two self tapping screws located belowthe ashtray opening (Fig.

10 10). Next unclip,lift and remove the transmission coverpanel from the console. It may benecessary on some models to pushforward slightly on the rear of this panel toclear the electric window switches.(Fig. 11). Disconnect all wiring plugsbefore this panel can be removed. Storethe transmission cover in a safe placebeing careful not to damage the painted front the radio removal tool (part number AU464 - available from SpecialisedService Tools & Equipment - Phone (08) 82692588), slide the radio out (Fig.