P38 4.6 HSE with LPG black smoke and miss fire

Hi all hope you can help me out with this it's my first Range Rover and I love it it's just a bit disappointing at the moment but I will persevere.

INFO :
P38 4.6 1997 190k on the clock, it has LPG but I have no idea if it works correctly (multi point).
I have no history on the vehicle

FAULT:
Thick black smoke on acceleration
Slight misfire ( more prominent on deceleration)pops and bangs not to loud.
After accelerating the revs drop right down 200/300 rpm sometimes stalls.
New fuel
Plugs look new
Only one warning on dash ( fuel gauge ) I will sort out once running right.

I dare say it's been talked about before I'm just hoping to piggyback on some of the knowledge and experience that is out there.
Thank you

I know nowt about the V8, but black smoke on a petrol usually means a very rich mixture.

Over fuelling will cause black smoke and the pops and bangs on over run - try to get it sorted before you roger the cat converters. Check air filter or simply remove it and see what happens, if no improvement it's probably diagnostics time.

Is it the same on petrol and lpg or just one fuel type?

its your 02 sensor/s switch it to petrol & drive it like you stole it

I'm no expert on this but it might be possible for your local garage to test the emissions and check if your lambda sensors are working, in that I believe that this is what is known as a closed circuit system whereby the ecu throws in the juice and this fuel trim is regulated but what the lambdas see?
Hence why the fuel injection should be better performing than a carb.
I reckon some of the more knowledgable guys on here will be able to offer better solutions especially those with experience of fitting lpg systems as these run of the info from the engine ecu and actually get info from it to run the lpg system.

forthbridge said:

I'm no expert on this but it might be possible for your local garage to test the emissions and check if your lambda sensors are working, in that I believe that this is what is known as a closed circuit system whereby the ecu throws in the juice and this fuel trim is regulated but what the lambdas see?
Hence why the fuel injection should be better performing than a carb.
I reckon some of the more knowledgable guys on here will be able to offer better solutions especially those with experience of fitting lpg systems as these run of the info from the engine ecu and actually get info from it to run the lpg system.

Click to expand...

Thats right. My 4.6 runs badly on lpg and the local specialist told me to run it on two or three tanks of petrol to set up the ecu then he could sort the lpg side out. Haven't got around to taking it back yet, on the to do list.

Thanks for the advice all of you, that was my suspicion ( over fueling ) as I have only just got the car I'm yet to put some LPG in it .
Time to remove the air filter and see what this V8 can do.

Hope it goes faster than my discovery 300 tdi.

Forgot to add : I will keep you all informed as to the results of said thrashing.........I mean drive.