disco v8 lpg backfire

[newto4]

Hi guys I have a 1996 3.9 v8 disco with LPG.It has an occasional backfire.
It seems to be backfiring in the exhaust rather than in the inlet. When it does backfire there is a momentary loss of power and the revs/rev counter drop.
She has a rimmers sports exhaust so no cats- I am therefore not concerned about damaging anything, I reckon the exhaust can can it.
If it happens in a built up area pedestrians run for cover asif they are being shot at.
Happened on M4 once when an a*se in a freelander was right up my chuff----he soon pulled back into middle lane.
So as the revs drop it can't be a single plug lead or a plug for that matter---any ideas?

[Range Rover Blues]

It's oftena sign of running lean, so does it do it when you need to fill up perhaps?  that's common.

Another thing, far more worh though, ours does it when it's eaten an exhaust valve, that said it blows the inlet away :-k
Does yours purr or chug slightly? if the later do a compression test.

[newto4]

It's oftena sign of running lean, so does it do it when you need to fill up perhaps?  that's common.

Another thing, far more worh though, ours does it when it's eaten an exhaust valve, that said it blows the inlet away :-k
Does yours purr or chug slightly? if the later do a compression test.

Doesn't seem to have any pattern at all- can go for days with no problems and then do it 3 times in as many miles.chug or purr---dunno really never thought it was a problrm though.

[Range Rover Blues]

Ok, another is to check the spark strength and quality, have you closed your plugs up to 27 thou?

What about weather/temp/humidity/pressure etc?  you'll probably not know but it might make you notice something.

Also, sometimes some systems like a different plug as LPG burns hotter IIRC (though slower, bizarely :-k) which can cause problems.

But as yours missfires after the engine I'm tempted to think it's an unbunred fuel issue, so check the mixture and the quality of spark.

[newto4]

Ok, another is to check the spark strength and quality, have you closed your plugs up to 27 thou?

What about weather/temp/humidity/pressure etc?  you'll probably not know but it might make you notice something.

Also, sometimes some systems like a different plug as LPG burns hotter IIRC (though slower, bizarely :-k) which can cause problems.

But as yours missfires after the engine I'm tempted to think it's an unbunred fuel issue, so check the mixture and the quality of spark.

Thanks for all the info---I am still trying to get my head around why the rev counter drops-where does the rev counter get its signal from? Also as the power dies off for a split second at the same time it can't be a plug or a lead as an 8 cylinder will hide that really well. It seems to be a momentary total loss of spark etc-thus unburnt fuel ends up in a hot exhaust and ignites