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Mazda 6 - LPG Conversion massive increase in fuel use - Apinargh

Happy New Year to all,

Just before Christmas I had my Mazda 6 (38-42mpg for 6 months prior to conversion) converted to LPG by a local dealer who has converted 4 previous cars for me without problems.

Since this conversion, though, the consumption of both petrol and gas is very lame, at about 21-23mpg. This applies to petrol as well.

the idling speed is high on starting from cold, and then begins to vary in rate, surging up to about 1500rpm every second, then dropping to 1000.

There is a considerable over-run when I throttle off.

Otherwise the ride is fine.

But there's no point converting to half price fuel if you then use it at twice the rate.

If anyone has any advice as to what he might have done or where we ought to be looking I'd be grateful. Sounds as if he's cocked up the engine management system, but how?

I am not knowledgable about engines, but I am very keen to see my investment bear fruit...


Mazda 6 - LPG Conversion massive increase in fuel use - Peter D

Take it back it will have a warrantee. Regards Peter

Mazda 6 - LPG Conversion massive increase in fuel use - unthrottled

Take it to any garage that does MOTs and ask for an emissions test. Post up your NOx, CO, and HC readings and a problem might reveal itself. They don't call propane 'pane' for nothing. It can be hard on petrol engines, burning slowly and resulting in high EGTs which can burn exhaust valves and melt cats. Beause it burns slowly it needs more spark advance than petrol. It's possible the conversion didn't dial a new spark map into the ECU. This wouldn't explain the poor consumption with petrol though.

Mazda 6 - LPG Conversion massive increase in fuel use - injection doc

Sounds to me like it has an air leak, this will cause high idle cold, erretic idle hot (hunting) and slow on overun to run down + increase in fuel consumption to compensate for a weak mixture.

I would take it back asap as you may burn a valve or cat!

Mazda 6 - LPG Conversion massive increase in fuel use - Steven Quas

You should expect a 15-25% drop in economy when running on LPG due to the lower calorific value compared with petrol and the sub-optimal injection process. That said, it does sound like the LPG injectors have not been fitted correctly - a common problem.

Steven Quas , Hamburg


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