Problems about poor MPG of LPG

[JJ]

Hi guys,

I recently bought a Holden Commodore 2004 3.8L engine which installed with LPG, branded “Sprint Gas”. The main reason I bought a LPG car is because I want to save money on my fuel expenses. But the problem I am having with it is that it is not performing good, in fact it is very poorly performing on the MPG, which is only 10.86 MPG travelled.

I have consulted several other same model car with similar LPG setting, and the feedbacks are all showing that the car should easily reach 19 MPG. Please advice on some possible fault on the car. Is it most possibly the fault happening on the LPG device or the engine of the car itself?

Appreciate any of the replies. Thanks.

Topic

[JJ]

Can anybody help me here ??

[EricTheCarGuy]

With MPG issues you have to start with the basics, regardless of the fuel used. In fact, I wrote this article addressing the common issues that cause problems with MPG. Perhaps read through it, try some of the recommendations, and let us know what you find.

http://ericthecarguy.com/faq/finding-and-fixing-the-causes-of-poor-mpg

Good luck and keep us posted.

[Bill]

There are several reasons for poor MPG on Propane. The most likely reason is running too rich. This can cause low power as well as low MPG. Not knowing the type or brand of system installed makes it hard to give much info. Running rich on LPG causes the engine to run very hot in regards to exhaust temps and can damage the engine.

It could also have a partially plugged catalytic converter if it has one installed.

You might end up having someone who specializes in LPG to address your problems.

[JJ]

Hey wysetech, thanks for your reply. Can you please explain what is running too rich? I have no idea what does that mean. Thanks.

[Wayne]

i.e. Too much gas, propane in this case, to air used for combustion.

[tadaskr]

I have LPG car too. Where I live LPG have 4 generations. 4th generation is when you have injectors to each cylinder. If this system in your car then try to look if there is some difference between gas and LPG. If there is then you need LPG checked

[Bojan Savic]

The first place I would look for when having problems with LPG system is cooling system.

I used to have (until I bought my mazda in 2012) a 1989 Yugo with LPG conversion (my dad converted it 7 years before I got the car), and having driven almost 100.000km on LPG I learned a couple of things about it.

There are two types of systems (main), one which feeds the propane into the intake manifold (good for older non fuel injected cars), and injected one, which is either single port injected or multi port injected (your one is most likely this one). If a fuel injected car is converted using the first method, it’s unreliable, poor on gas, can cause an explosion and will not pass state inspection (at least in Serbia), if your car is fuel injected, and all you have of LPG installation in a small hose going into the intake, that’s your problem. Older systems can be adjusted with two knobs on the evaporator, one controls the idle, the other (bigger one) controls the main mixture, on EFI cars, LPG ecu does that. You can try to manually adjust your system to some rough parameters which would be better than having the system way rich or lean. You would first adjust the big knob so the car can rev nicely (linearly, so it doesn’t loose grunt at high revs), and then adjusting the idle (smaller) knob (always with headlights on, older LPG systems are very sensitive to engine load at idle). Last comes the fine tune, for which you will need two people, one person will go and look at exhaust fumes, while the other will turn the knobs very slightly, what you are looking for is constant flow of gases, not poof,poof,poof kind of thing. If you can I would urge you to take the care to LPG system service station, because they have equipment which measures CO2 coming out of the tailpipe and can tune the system to the nearest millimeter, and can also clue you in if your engine is burning oil.

Another thing which is very important is a good cooling system, because LPG as it’s name stands for is Liquified Petroleum Gas, which is stored at high pressure in liquid condition, so it has to evaporate in order to be used by your engine. Evaporation is a process which causes cooling, and also needs enough heat in order to be efficient. So if your car is low on coolant, the first thing to suffer is the evaporator, which is consequently the highest in the system. When that happens, the evaporator cools down (and can even freeze, sometimes also crack), and evaporation process doesn’t happen at full efficiency, resulting in Liquid propane entering your engine/intake manifold, causing the car to run very rich. So make sure your thermostat works (especially in winter), your system is at proper water level, and that the coolant is clean and flows freely throughout the system. When installing LPG people usually tap into the heater hoses, so a bad (clogged) heater core can cause issues with proper flow to the evaporator.

Also the evaporator has a membrane inside it which is essential for good and efficient operation, and gets old dirty and brittle over time, around 50.000km and has to be changed by a professional, good thing is it costs as much as a regular air filter. Another very important part is the fuel filter which will clog up with metal particles that come off inside the tank.

Hope I helped a little, if you have any questions feel free to ask.

[Author]

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