I used to get around 450-500km in city driving and 600km on highway driving out of about 60-65 litres of LPG.

Now its down to about 450km of highway driving and maybe 350-400km of city driving.

I haven't changed the o2 sensor and wont prior to asking if anybody knows whether this LPG system needs any sort of regular maintenance or service or tuning to keep it running optimally.

Its an impco system that's done around 70,000km since I had it installed and thats about all I know about it. Heres a pic of the converter and mixer. What does the solenoid cable tied to the gas supply line at the top right of the first pic do?

I'd try taking it to an LPG installer, and getting them to have a look and just give it a basic tune (like you would a carby) because it's probably running a bit rich. They'll probably just check the A/F ratio at the tailpipe, adjust the mixture and go from there...

I have the factory fitted IMPCO system, but my last tank I averaged 25L per 100km, but I think it's more to do with my heavy right foot

Jared

EDIT: little thing you're talking about in the above picture adjusts the mixture on the fly (well on mine i have two and thats what they do,but they're mounted right close to the mixer)

I'd rather DIY, that way I know I've returned all bolts and not taken any intentional shortcuts. I also get the satisfaction of learning something I may not have known before.

I'm trying to do some research on the system and have discovered (as you said) that it adjusts the mixture.

I'm trying to find more info (bloody difficult) on how to correctly adjust the tune on this car.

I'm tempted to hook the CRO up to the EGO sensor and see how often it jumps from 0-1 volt and on the second trace measure what the LPG computer is doing to that solenoid. I guess this would tell me if its correctly adjusting rich > lean > rich or if I have a seperate engine fault or whether the EGO sensor is working or not by flicking it back to petrol and seeing if the 0-1v sensor output responds...

Look for your gas computer - I have the same mixer as you, and my computer is the Impco "oz" something-or-other.

The computer opens and closes that solenoid rapidly, and you can check it with a multimeter that can handle duty cycle.

You need to warm the car up, and adjust your mixture till the oz computer is controlling that solenoid at around 50% duty cycle (equal amount of ON and OFF time, or OPEN and CLOSED time).

If you can see it running near 100% or 0%, the computer is trying to richen or lean out the mixture to the extreme, but is running out of "duty" to do so.

Its a service item as well, and can wear out fairly quickly.

All the above assumes your O2 sensor is working correctly of course.

Is it still running on petrol? If so, hows your economy on that?

Haven't checked economy on petrol, I only run it on petrol once every few days for a few mins in the morning till the motor warms up then do another tankful of LPG until touching the petrol again. I go through perhaps 10 litres per month of petrol, considering the cost, I'm not that interested in using it except for the purpose of keeping the injectors alive.

To answer your question, the car runs almost identically on petrol as it does LPG but I dont know the economy of it.

I'm going to check the LPG system more over the next week and see what I can discover.

Thanks for your reply

No worries. reason I asked about the petrol is to determine if your O2 sensor was in OK condition.

I'm in the same boat as you at the moment. Was on similar economy when first installed, now its getting a little worse. I'm going to throw the meter on mine as well, but I think my bad economy is also due to the thicker oil i'm using.

another question I couldn't find an answer to on google but how do spark plug colors respond to rich/lean LPG mixtures?

Is it the traditional black for rich and tan-whitish for lean or something else?