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PostSubject: LPG FAQ   Mon Jan 28, 2013 11:32 am

LPG FAQ

I am not an LPG installer but do read lots of threads and ask lots of questions.

What are the main types of LPG systems?

Singlepoint - This is where the gas enters the intake plenum at a single point (throttle body) It is mixed with the air from the air intake and enters the combustion chamber from here.

Multipoint - Exactly that. Holes are drilled in the intake plenum and injectors squirt LPG directly into the combustion chamber (same as your petrol system)

Both will have their own ECUs or Lambda control units which control the amount of LPG used.

Multipoint is more fuel efficient but more expensive.

What about "blowbacks"?

A blowback tends to occur more with singlepoint systems and can blow an airbox apart (trust me on this) It can also take out a mass air meter (and this Evil or Very Mad ) They occur when the gas is not burnt completely - usually when the mixture is too weak.

So I will always get blowbacks on singlepoint systems?

No you will not. The system needs to be set up correctly by somebody who knows what they are doing and has the correct kit to do it. Make sure that plugs and leads are in good condition as LPG is less forgiving than petrol.


Can I fit myself?

Yes if you feel competent. However you must get it certified by a qualified LPGA registered installer. Check with your insurance company if they will allow this. Some insist on professional fitting not just certifying.

Where does the tank go?

Entirely up to you. Can go in the back of a LWB but you lose a seat to get it in (maybe two). You can get a smaller petrol tank fitted so that the gas tank goes under the car next to it. This way you don't lose any seats and it looks neat. This is unsurprisingly the most expensive option.

Can you fit LPG to the GDi engine?

You can but it is not a good idea. Injector tips burn out with it. Normal thinking is that petrol cools the tips in normal running. When the emulator for the LPG shuts the petrol injectors down they overheat and burn out the tips. I have recently discovered that what actually happens is a small amount of petrol sits in the injector. This gets heated by the combustion process of the LPG and gums up the injector. Same result but a slightly different reason. Either way, don't do it. I will get posts saying that people have it fitted and it works fine. Go with the majority (including most LPGA installers) and don't fit LPG to the GDi. Sorry folks - buy the 24 valve instead.

Can you use LPG on diesel engines?

Sort of...

It works differently in so much as a diesel engine cannot burn just LPG. The gas is injected with the diesel. This helps the normal fuel to burn more efficiently an produce less emission's with more power. It is a specialist system and quite expensive due to its limited appeal. You still use diesel, just more effectively.

Is it worth fitting?

Only you can decide that. Get a few quotes from LPGA installers first. Then work out how many miles you cover in a year. You get slightly less MPG from LPG than petrol but the price is around a third.

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Father Tiresias
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PostSubject: Re: LPG FAQ   Wed Feb 06, 2013 1:09 am

As someone that has been fitting LPG to and running vehicles powered by LPG for the last 15 years may I just clarify a couple of points in the above FAQ:

LPG systems nowadays fall into three different categories:

1. Single point open loop - Very close in principle to a carburetor. No ECU's are involved. A venturi/mixer is fitted usually between the carburetor and the inlet manifold. The LPG delivery is made from a reducer through this venturi/mixer and the quantity is controlled by the depression into the manifold, much the same way as a carburetor delivers petrol. These systems are very simple and extremely suited to older non-ecu controlled engines. They can be fitted in less than a weekend and for minimal cost.

2. Single point closed loop - Similar to the above but with the addition of a lambda sensor and a simple ECU to control a delivery valve to ensure better control over the mixture.

3. Multipoint closed loop - Typically each cylinder has an ECU controlled LPG injector. In many many multipoint systems the LPG ECU piggybacks onto the petrol ECU and uses information from the petrol ECU and its sensors. Some multipoint systems will use their own sensors. Multipoint systems are generally more efficient than single point and there is less of a perception of reduced power when running on LPG.

Blowbacks:

Usually occur when the system leans out for some reason. This is typically due to air leaks or changing from petrol to LPG whilst the throttle is open. Blowback arrestors can be fitted between the air box and the engine which virtually eliminate the possibility of damage from a blowback. If a system is correctly installed, correctly set up and used properly it should never blow back anyway.

LPGA Certification:

Is not a legal requirement and not all insurance companies require it. The LPGA is a fee charging organisation that ANY installer can join regardless as to how competent they are. Joining the LPGA is a bit like joining a Golf Club. Any one can become a member but it doesn't mean that you are any good. In fact I have had to rectify systems that have been LPGA certified that were on the border line of being mobile bombs. Do not put too much importance on LPGA mebership or system certification when choosing an installer. Look at the quality of their work and talk to previous customers. It is far more value than an LPGA certificate

LPG & diesels


Unless a diesel is specifically designed to run on LPG (some forklifts for instance), LPG on diesels is usually a supplementary fuel. It's use in general is to provide an increase in power. CNG (compressed natural gas) is more commonly used commercially on diesels and a number of bus companies use CNG powered vehicles).
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PostSubject: Re: LPG FAQ   Wed Feb 06, 2013 10:33 am

Thanks for the update Father Tiresias Bow

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PostSubject: LPG servicing?   Wed Jul 17, 2013 4:29 pm

Can anyone explain what servicing is needed by an lpg coverted engine in addition to the normal fluids etc or a standard petrol service.
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PostSubject: Re: LPG FAQ   Wed Jul 17, 2013 5:55 pm

It depends on the type of system fitted but generally there is a filter somewhere in the LPG line or vapouriser that should be replaced. Obviously condition of pipework and wiring is important and checking all pipe joints, fittings and solenoids for leaks using either soapy water or proper leak checking fluid is a good idea. The byproduct of using LPG is a treacly substance known as heavy ends which collect in the vapouriser. This should be drained out. Other than that, just setting up idle and emissions as you would with a carburated engine.

Condition of the ignition system is as important as the LPG kit itself. Good quality components should be used and should be kept in good condition.

If the engine does not run right on LPG and everything else checks out Ok rebuild kits can be obtained for most vapourisers.
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