LPG

[hondamake]

When running on gas you need to switch off the petrol injectors, you can cut the live feed via a relay but on everything other than very early basic injection systems this will throw a fault code. It may even push the car into limp mode. The correct strategy is to break into the signal wires and divert the signal via an emulator. There are a number of different makers/types, some of which are vehicle specific, but all use the same basic principle. The default status of the emulator, when it is not energised, is to give a direct connection i.e. no interruption. When the emulator is energised it disconnects the injector but provides a return of the correct impedance to the vehicle ECU. Two methods of install; either cut & solder or an emulator harness with 4 female and 4 male injector plugs - pull the female off the petrol injector, replace it with one on the harness and plug the corresponding male into the petrol female.





Uploaded with ImageShack.us[/img] If you're still awake we can do vapourisers next!

[Dodo Bizar]

I edited your links, check the third photo, we get full size that way! Can we get the full size versions for the other photo's as well? It's probably a dfferent link your using there.

[hondamake]

Thanks for the edit, as you've probably guessed computers are not one of my talents! I'll do a little research on how to post images properly.

[hondamake]

Hi Guys. Sorry about the big pause, I'm a lion. Anyhow on to vapourisers: When you fill the tank with gas it is pumped in as a liquid and contained under pressure. It leaves the tank as a liquid, via a pick-up tube, forced out by the saturated vapour pressure which develops above the liquid gas. When it reaches the engine bay it has to be converted into a saturated vapour at just above atmospheric pressure. As per the physics you remember from school the energy required is drawn from the immediate surroundings creating a big temperature drop. To avoid the vapouriser freezing it has a water jacket fed from the engine's cooling system, usually by diverting the heater flow. Vapourisers are usually 2 stage, first a drop to 2 bars then a tuneable drop to the required pressure. I'll post some photos of the kit on my daily driver, a Mazda 626 with a 2ltr FS motor.

[Dodo Bizar]

Good to see you again . Keep the thread up, I am really learning from it.

[hondamake]

You now have the three main front end components: Emulator, mixer and vapouriser. They are common to open and closed loop strategies. For open loop you will also need a dashboard petrol/gas switch incorporating a RPM controlled safety over-ride. Unless the engine is running the gas shut-off valves will close, thus preventing unburnt gas accumulating. If you are using an ECU contolled stepper valve, closed loop, this feature is already incorporated. I will draw a wiring/pipework schematic, scan it and attempt to upload it. Next is injection.

[saxophonias]

Could you mention some prices for the lpg system installed to cars? In Greece it has become very fashionable these days but I am afraid that they overprice it. Imagine, installing this system to a civic (multipoint cars) cost about 1500euros. Isn't it a great deal of money or what?

[hondamake]

Hi Saxo. As mentioned before 3 strategies:
1. Open loop; requires a vapouriser £60, mixer £20, emulator £30, dashboard switch £20, pipes & clips etc £20 = £150
2. Closed loop; as above plus a controller ECU which incorporates a dash switch + £120 - £20 = £250
3. Injection; for a 4 cylinder kit £300 but the price rises for 5 cylinder and above to £500 plus.
A rear end kit of tank, filler etc. starts at £100, maybe £250 for very large/ unusual tanks is common to all of the above.
These prices are for new components which are readily available on eBay etc. DIY fitting is simple for any home mechanic/enthusiast. Used parts are much cheaper.
When LPG first became popular in the UK £1500 - £2000 plus vat was usual for an install, prices now start at £795 inc vat for a 4 cylinder car. God bless our Polish cousins !

[hondamake]

Right, wake up at he back! Injection systems utilise a similar vapouriser but it delivers vapour to the injectors at between 1.2 bar and 2.0 bar, dependent upon engine type. Generally the higher the engine power output the higher you set the pressure. The gas injectors are similar to petrol injectors in so far as they have a constant output volume, fuelling is modulated by injection timing. This timing is controlled from a "stand-alone" gas ECU which reads a number of inputs. Gas temp, water temp at the vapouriser & gas pressure. It also reads a lot of info from the cars own ECU, it does this via the emulation interuption. As with open/closed loop systems you have to break into the petrol injector signal wires. This time as well as switching off the petrol and emulating the correct resistance it also reads the car's fuelling strategy. Every sensor input into a car's ECU is to control injector timing and ignition advance/retard. The gas system piggy-backs this info.

[mynameisowen]

Instead of having this piggyback LPG ECU could you not map the standard ECU to operate on LPG?