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Author Topic: Fitting LPG - Electrical Connections  (Read 4807 times)

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Kevin Wood

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Fitting LPG - Electrical Connections
« on: 06 April 2010, 10:02:11 »

Connections to the engine ECU and battery

The LPG system needs the following connections from the car's electrical system to supply power to the LPG system, in order to determine the engine operating conditions and also to allow the Lambda sensor output to be available during system calibration:

  • Permanent 12v supply
  • Ignition switched 12v supply
  • RPM (Tachometer) signal
  • Lambda sensor output(s)
In addition to this, the LPG system needs to intercept the signal to each petrol injector in order to determine the time and duration of the injection events and to allow the petrol injectors to be disabled when running on LPG.

For the switched 12v supply, RPM and Lambda sensor signals, the most convenient place to intercept these is probably where the wiring emerges from the engine ECU in the triangular plastic box next to the battery.

An easy way to find the connections is to dismantle the connector(s) which plug into the ECU and to find the numbered pin corresponding to the signal of interest. On the X25XE, X30XE and X20XEV engines it is reasonably easy to solder additional wires to the pins in the connector. On the Z22XE, Y26SE and Y32SE engines, the pin pattern of the ECU electrical connector is too dense and it is better to identify the wire by finding the connector pin, but follow it a few centimetres up the loom before stripping the wire, soldering a connection to it and protecting with heat-shrink sleeving.

The following table indicates on which connector pins these signals can be found for each of the petrol engine options and the colour coding of both the vehicle wiring looms and the Stag LPG system looms:


Engine TypeY26SE/Y32SEX25XE/X30XEZ22XEX20XEV
Signal NameLPG Loom Colour
Switched 12vRed(thin)X86 Pin47 BlackPin27 BlackX84 Pin64 BlackPin17 Black
RPMBrownX86 Pin35 GreenPin43 GreenX84 Pin62 GreenPin20 Green
Lambda Sensor 1VioletX85 Pin28 BluePin28 Brown/BlueX83 Pin57/8 Black/GreyPin36 Yellow
Lambda Sensor 2Violet/GreyX85 Pin44 BluePin47 Brown/BlueN/AN/A

On the Z22XE, Y26SE and Y32SE engines there are two connectors on the ECU and we indicate above which connector is applicable. On the Y32SE/Y26SE X86 is the connector where the loom emerges and heads through the bulkhead into the car interior. X85's loom runs across to the cable tray on the engine.

On the Z22XE, X84 heads to the bulkhead while X83 heads to the engine.

The permanent 12v feed (the thicker of the two red cables in the Stag loom, with an inline fuse holder near the end) can be taken directly from the battery positive terminal. Ensure all other electrical connections have been made before connecting this (or leave the fuse out until you are ready to test).

The ground connection for the LPG system emerges on a thick brown wire next to the permanent 12v feed. this can be connected to the battery negative terminal.
« Last Edit: 06 June 2010, 17:08:03 by Kevin_Wood »
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Kevin Wood

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Re: Fitting LPG - Electrical Connections
« Reply #1 on: 07 April 2010, 18:16:40 »

Injector Connections

The LPG system looms are supplied with "piggy back" connectors to make a connection to the petrol injectors and to their corresponding connectors on the vehicle loom.

The LPG ECU contains a switch that allows the signal to the petrol injector to be passed through to the petrol injector when running on petrol. When switching to gas, the petrol injector is disconnected from the vehicle loom by the LPG ECU, which then begins operating the corresponding LPG injector, triggered by the signal that once operated the petrol injector.

At the same time, a load is applied to the petrol injector signal so the vehicle's engine ECU doesn't sense an open circuit.

The Piggy Back connectors consist of a female and male connector for each cylinder. The male connector plugs into the vehicle loom and the female connector plugs into the corresponding petrol injector.

Because the ECU fires the injectors sequentially, it is important that the injector wires are not crossed over between cylinders.

Note that although the LPG loom piggy back connectors are numbered from 1 to 4 (4 pot) or 1 to 6 (6 pot) these are for identification only and do not have to correspond to cylinder numbers on the engine itself. They do, however, correspond to the numbers shown in the ACGasSynchro software and I will refer to these as channel numbers to avoid confusion.

On a four cylinder engine it makes sense to keep the channel numbers corresponding to the cylinder numbers but on a V6, channels 1,2  and 3 are grouped together in the wiring loom and channels 4,5 and 6 are separate. it makes sense, therefore, to use channels 1,2 and 3 for one bank of the engine (e.g. cylinders 1,3 and 5) and channels 4, 5 and 6 for the other bank, in order that wiring to the individual injectors does not have to cross over the "vee" of the engine.

On a V6 engine, the "piggy back" connectors can be made to fit under the plenum in the spaces around the intake manifold. This is not particularly pretty, but it makes installation easy. It may be necessary to remove the original injector loom from its' cable tray to gain more space, in which case it should be laced with insulating tape for protection.

On the 4 cylinder engines, the injector connectors are integral to a cable tray that sits over the petrol injectors. Either the piggy back connectors can be discarded and the LPG loom spliced into the vehicle loom, retaining the cable tray, or the cable tray can be discarded after first removing the injector connectors from it, and the piggy back connectors used. The latter method also frees up some space for the LPG injector pipes to feed down to the manifold.

General instructions for splicing into the vehicle's loom rather than using the piggy back connectors are included with the LPG kit so will not be repeated here.

Make a note of the LPG injector channel numbers that correspond to each cylinder number, as you will need this information when installing the LPG injectors.
« Last Edit: 08 April 2010, 09:42:34 by Kevin_Wood »
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Re: Fitting LPG - Electrical Connections
« Reply #2 on: 08 April 2010, 09:53:41 »

Connections to other LPG system components.

Most of the other connections to components in the LPG system are easily made because the correct connectors are already supplied fitted to the LPG system wiring loom.

It is best to identify these with the loom spread out on the floor, before it is installed in the vehicle. The correct connections can normally be determined by the connector type, with any ambiguity resolved by checking the colour coding of the wires entering the connector with reference to the wiring diagram in the Stag manual.

Identify the connection to each system component on the wiring loom and decide on their installation locations in the vehicle before installing the wiring loom. Take the wiring loom and separate and group the wires depending on the direction they need to head, working from the ECU outwards. For example, the connections to the battery and engine ECU need to head across the bonnet slam panel from an ECU mounted under the offside front wing, whereas the switch / control panel, temperature and pressure sensor wiring will need to head back towards the bulkhead.

Cable tie the loom to maintain the cable grouping before offering it up to the vehicle and finding convenient locations for the wiring. The wires can then be cable tied and clipped into position. Any wires that are excessively long can be handled by deliberately routing them via longer routes or by doubling them back in the bundle of cables to lose unwanted length.

Connections for which connectors are not already present on the LPG loom are handled as follows:


« Last Edit: 12 April 2010, 12:46:06 by Kevin_Wood »
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Re: Fitting LPG - Electrical Connections
« Reply #3 on: 12 April 2010, 12:24:00 »

Vapouriser and Tank gas valves

The gas valves at the tank and the vapouriser control the flow of liquid LPG from the tank into the vapouriser. The flow is controlled at both ends of the fuel line to ensure that residual liquid in the fuel line does not continue to feed the vapouriser after the engine has been stopped, and also that, if the fuel line were to be ruptured, the feed of fuel would be isolated automatically at the tank.

These two valves are operated from a single output on the ECU and must be connected in parallel. The output on the Stag loom emerges as a pair of wires colour coded blue and black, with no connector fitted, in an overall black coloured sheath. The blue signal is a switched +12v output and the black signal is internally connected to battery negative.

Normally, the Voltran vapourisers require a pair of spade connectors for the front end valve, and the wires should be soldered into the spade connectors along with a pair of wires from the 4 core cable that runs parallel to the fuel line into the tank valve box. It is normally not possible to continue the blue and black colour scheme so just pick two conductors in this wire and ensure that the correct pair are connected to the valve at the other end.

Tank valve connections vary depending on the type of tank and valve used. Normally, polarity is not important, but if the tank valve is marked with positive and negative symbols or red and black colour coded wires, the red (positive) side should be fed by the blue wire from the Stag loom.
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Re: Fitting LPG - Electrical Connections
« Reply #4 on: 12 April 2010, 12:34:49 »

Tank level sensor

The tank level sensor on the Stag kits normally takes the form of a variable resistor whose resistance varies from about 0 to 90 ohms depending on the liquid level in the LPG tank. This is a "two wire" device.

The Stag ECU and loom make provision for this type of level sensor and, in addition, for an alternative type that connects using 3 wires, having, in addition, a power feed.

The level indicator signals on the Stag loom terminate in 3 wires without a connector fitted, colour coded Red, Black and White, in an overall black sheath.

The red wire is a power feed to the sensor, not normally required for a two wire sensor. This can be ignored but the end must be protected from shorting. It is suggested that the cut end of the red wire is insulated with either heat shrink sleeving of insulating tape. It can then be bent back on itself and the end pushed back into the black overall sheath to protect it from damage.

The red and black wires should then be connected to the 2 remaining conductors in the 4 core cable that heads to the tank valve. Once again, the colour coding may not be possible to maintain but as long as the correct colours are used at both ends of the wire all will be well. It is not normally important which way round the two wires are connected to the sensor but the white wire is normally the signal (positive) connector whilst the black is a battery negative.

It is best to run the sensor signals to the vapouriser as this is where the other two conductors in the 4 core cable to the tank valve will be connected.
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Re: Fitting LPG - Electrical Connections
« Reply #5 on: 12 April 2010, 12:45:52 »

Control panel / level indicator

The wiring to the control panel / level indicator (and, incidentally, the small black warning buzzer) emerge as 6 wires in a black sheath from the Stag loom. These are colour coded White and Green, Grey and black, Green and Red and White and Red, Black and Red.

Before connecting, these wires must be fed through the bulkhead to the dashboard area and a suitable location for the control panel chosen.

On drive by wire vehicles, a convenient location to feed the cable through the bulkhead is where the throttle cable would otherwise emerge, just to the offside of the brake servo. There is a rubber blanking grommet fitted here which can simply be pierced to allow the cable through.

Failing this, the rubber grommet where the heater matrix pipes pass through the bulkhead can be pierced.

The control panel requires a single hole in the dashboard at the chosen location through which the wires from the Stag loom must be fed. They can then be cut to length and connection of the control panel can be achieved by soldering the wires on the loom as per their colour codes to the matching wires on the control panel, making sure that the self-adhesive pad has been stuck to the control panel beforehand. This will leave you with a red wire left over. This is the feed for the warning buzzer (red wire on buzzer). The black wire from the buzzer shares the control panel's negative connection (also a black wire).

Once all the wires have been joined, they should be heat shrink sleeved and wrapped in insulating tape. Then clean the area around the hole in the dash using methylated spirit or isopropyl alcohol before pushing the panel up to the dash and securing with the self-adhesive pad.
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