Lambda systems are used to control the mixture of 'gas' (LPG/autogas) and air to acheive the best drive and economy from early injection and carb engines. They can be used on any vehicle which has a lambda probe, or oxygen sensor, fitted in the exhaust. These are normally found either directly in the exshaut manifold or in the down pipe just before the catalitic converter. On later vehicles they will also be a probe fitted after the cat, but this probe is of no use to the lpg system.
There are several different makes of Lambda control systems on the market, but they all work in a similar way. The only real difference between manufactures is the software and connection lead that is used to comunicate with the system. Somtimes this takes the form of a hand held tester, but more often it will be via a laptop pc.
Listed below are the most common systems that are readily available on todays market. I fit these on a regular basis, they both work very well.
VIP 100A
The vip 100A is a simple to use highly effective control system that has the bennifit of being able to be added to any exsisting system. It is a stand alone, so if you already have a open loop LPG kit you can add this to make it closed loop.It requires very few electrical connections and is capable of emulating the lambda signal to the petrol ecu.
Connection.
If possible I always route the wires so that the control box can be in the cab, this will make it a lot easier to check the mixture during test drive. There are two looms, one connects to the stepper motor, the other requires connection to various points of the engine or LPG system.
Blue wire & Red wire: Connect these to the positive wire on one of the LPG shut off valves, (usally a blue wire) This will power the box when the engine is running on gas.
Purple wire: Connects to the signal wire of the throttle position sensor (TPS), to check which wire this is, turn on the ignition and measure the voltage of each wire (normally 3) whilst fully opening the throttle. The wire that gives a varying voltage, 0-5volts, is the wire you need the connect to. (narmally the midle wire but check it!)
Green wire: If you vehicle has a lambda probe fitted you must identify the signal wire. If it is a single wire probe, normally fitted in the manifold, this is the only choice you have! However the most common probe has 4 wires (three is also
quite common) Four wire probes quite often have two whites, one grey, and a black. Check that the black wire has a varying voltage (usally 0-1v)
((although 0-5v is also quite common)) Connect to the wire with the varrying voltage.
Emulating the lambda signal: Emulating a probe signal means to send a signal back to the engine ECU that will tell it that the mixture is correct regardless what it really is. In other words it lies to the car! This means that there should be no
problems with engine check lights. To do this you must cut the signal wire from the probe and connect the green wire to the probe side of the cut and the white wire to the other end (the end that goes back to the engine ECU)
Important. do not cut the wire or attempt to emulate the signal on Landrover engines, range rovers, discoverys, ect. they will not tolerate this. Just tag the green wire to the signal wire of the probe. If any vehicle does not run correctly on petrol after
emulating the probe, remove the white wire and reconnect the probe wire, leaving just the green connected.
Also check that the vip box is only live when the engine is running on LPG, if it is live with the engine running on petrol the petrol ECU will receive a emulated signal, which will mean it will not correct the fuelling. The result will be very bad running.
Setting Up
Fit the stepper motor into the low presure gas pipe between the vapouriser and the mixer, do not plug in the loom, run the vehicle on gas and monitor the control box. The panel in the top right hand corner should show either a red or a green light, the red light shows a rich mixture, the green a weak mixture.
Adjust the vaporiser until the red and green light switch altertnatly, they may hang a little either way but this is to be expected. Adjusting the trim screw in the
bottom of the box will make a orange light come on, if you connected the purple wire to the TPS set the orange light to be off at idle and on as soon as the throttle is opened. If the purple wire is not connected set the orange light to be on at all times, Now plug in the stepper motor, the switching of the red and green lights should now become more constant. Adjust the vaporiser if neccassary. Check that when the engine revs are increased sharply the red light holds on. This should also be the case when you are driving. The red ight should stay on under hard
acceleration, then the lights should toggle once you are crusing. if this is not the case readjust the vaporiser.
Typical single point system components
Leonardo/Pegaso Control System
As mentioned previously the leonardo is basicly the same as the Bigas Pegaso, and the OMVL Millenium. I tend to use the Bigas Pegaso unit as it is a little cheaper!
These systems are ideal for new conversions as they include all the under bonnet wirring needed for the the LPG system.
The main loom consists of the large plug that connects to the control box, a small loom with a four pin plug connects to the stepper motor and the remaining wires need to be connect as follows.
Brown
Connect to tachometer signal, or - (negative) side of ignition coil.
Blue/Yellow
Connect to the signal wire of the throttle position sensor (TPS), to check which wire this is, turn on the ignition and measure the voltage of each wire (normally 3) whilst fully opening the throttle. The wire that gives a varying voltage, 0-5volts, is the wire you need the connect to.
Blue
Connect to the LPG solenoids - tank/s, shut off valve, vaporiser should all have a common live wire which is powered by this blue wire.
Red
Ignition fed live, ensure that the fuse provided is fitted and a good feed is selected.
Red/Black
Battery positive, permanent live, - ensure that the fuse provided is fitted in this wire.
Black
Connect to the negative of the battery. Ensure a good clean connection.
Orange
Optional tempreture sensor wire. This is rarely used
Yellow & Yellow
The two yellow wires can de used to disconnect the petrol injector positive on some vehicles. However in most cases a emulator will be used to do this as check light problems can occure. It is also possible to use the yellows to cut the live feed to the petrol ECU when the vehicle is not in use, this can be helpful to reset fuel trims, to reduce the risk of check lights. The function is switchable from the laptop.
Purple
The purple wire connects to the signal wire of the lambda probe (oxygen sensor)
If you vehicle has a lambda probe fitted you must identify the signal wire. If it is a single wire probe, normally fitted in the manifold, this is the only choice you have! However the most common probe has 4 wires (three is also
quite common) Four wire probes quite often have two whites, one grey, and a black. Check that the black wire has a varying voltage (usally 0-1v)
((although 0-5v is also quite common)) Connect to the wire with the varrying voltage
If your vehicle does not have a probe fitted it is possible to retro fit one in your exhaust.
Grey
Emulating the lambda signal: Emulating a probe signal means to send a signal back to the engine ECU that will tell it that the mixture is correct regardless what it really is. In other words it lies to the car! This means that there should be no
problems with engine check lights. To do this you must cut the signal wire from the probe and connect the purple wire to the probe side of the cut and the grey wire to the other end (the end that goes back to the engine ECU)
Important. do not cut the wire or attempt to emulate the signal on Landrover engines, range rovers, discoverys, ect. they will not tolerate this. Just tag the purple wire to the signal wire of the probe. If any vehicle does not run correctly on petrol after
emulating the probe, remove the grey wire and reconnect the probe wire, leaving just the purple connected.
Basic Setup
Connect your laptop to the system via the serial connection lead, open the software by clicking on the Pegaso logo. Go to vehicle configuration.