Vehicle & Technical > Discovery
Misfire...but only on LPG
JumboBeef:
Update:
mmmmmmmmmmmmmmmmmmmmmm
The backfire has *almost* totally gone, but not quite. I still get a rare misfire
The leads certainly helped. The only thing left to change now is the plugs, so I will do them this week.
Range Rover Blues:
Just to put it into perspective, regular unleaded is about 95 OctANE (RON), LPG is approximatley 115 octane.
Octane is a measure of how hard it is for fuel to self-ignite under compression and as spark ignition works by causing auto-ignition due to a shock wave, the octane rating of the fuel relates directly to how hard it is to ignite.
That's more than 20% harder to burn.
Also the burn temp of LPG is different and it takes longer to burn.
The backfire could be due to a weak spark, one tha's fine for petrol but not LPG. Alternatively it could be a weak mixture which can in turn lead to overheating plugs or other problems associated with missfiring.
I've just traced my missfiring to a dodgy coil, it was fine when cold but if the car sat in traffic for example it would missfire on LPG and oddly it begain to effect it's petrol performance too, not missfiring but it wouldn't pick up from idle smoothly, it was all or nothing.
Worth mentioning that if the spark doesn't happen in the cylinder then it has to go somewhere, in time that can cause damage.
JumboBeef:
--- Quote from: Range Rover Blues on February 15, 2010, 00:06:53 ---If you are buying new then fit NGK BP6ES, not BPR6ES.
--- End quote ---
Fitted new BP6ES today, then drove 60 miles and no backfire! :dance: The plugs which came out were BPR6ES (fitted by me last year :oops: )
What's the difference between the two types?
Range Rover Blues:
R is for resisted that's all, it's a radio surpression resistor but if you have quality silicone leads then they will be surpressed already. The resistor saps a little of the spark power so BP6ES are better for LPG.
JumboBeef:
Thanks!
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