Range rover black soot on start up

Hi folks , having troble with range rover classic, runs on both petrol and lpg. The problem i have is when started on petrol it chucks a black suit out the exhaust when started and will not idle properly, but when started on gas it doesnt do this and idles and tuns perfectly.

What would cause petrol side to do this?
Thanks

Could be sooted up Injectors...

If running on Gas, the Injectors get fouled up with deposits and instead of producing a fine atomised spray of fuel, they dribble it in which doesn't burn and mix as effectively.

With a LPG conversion, they do reccomend to run it on Petrol a few times a month to keep the injectors lubricated and clean...

Could try some of that Redex Injector Cleaner stuff and see what happens....

The other thing could be a split in the induction ducting allowing excess air in....If it is a Single Point system when on LPG the system doesn't measure the quantity and mass of air and just squirts gas in but on Petrol it needs to measure the Air intake through the MAF, if there is a split further up the past the MAF, the engine isn't getting the correct Fuel/Air mixture to run corerctly.

LPG Backfires are notorious for splitting intake ducting.

Thanks will give it a try , when i say it doesnt idle right i mean it can sometimes cut out totally and can be spluttery. Could it be the maf?

rangerover8 said:

Thanks will give it a try , when i say it doesnt idle right i mean it can sometimes cut out totally and can be spluttery. Could it be the maf?

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Could be. Also check petrol pump/filters. As Saint.v8 says worth putting some injector cleaner in to see if that helps. Use one bottle when petrol tank is below 1/4 full.