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.