LPG misfire

I changed the plugs in my 95' 3.9 v8 disco 1 and now when im running on gas once its warmed up i get a misfire. (it was quite bad up untill the centre box fell out the exhaust no its quite mild), ive been told that if i reduce the plug gap by around 0.2 mm it should solve the problem, does any know if this is true or if id be wasting my time??.

or is there a common problem with misfires that im overlooking?

I have had the odd blow back throughout the air box on gas when setting the old single point system up. That's caused by not having enough gas in the mixture.

Never had a back fire through the exhaust though so can't offer any advice on that sorry.

.....gap the new plugs like the ones you took out and see if it dissapears first.

Are they the correct plugs.

Are your cap and leads gen items as non gen can cause problems too

Have also heard that LPG prefers the older copper type of plugs rather than the new platinum/iridium ones, but I have no tried them yet.

i also have a problem with back fires through the air box and a mis fire on gas when warm, my lpg installer told me to check the ht leads as they could knackered, and thinking back too when i changed the manifolds i did take 2 ht leads off and they seemed welded to the plugs as well so doubt they have been changed for a while. got some 8.5mm magnecore leads arriving on saturday and new plugs. hope its the cure V6/7 and a halfs are even more thirsty

vougese39 said:

Are your cap and leads gen items as non gen can cause problems too

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^^^ What he said! - Magnecor are good, but for the money, genuine parts are much better

steadyaway said:

Have also heard that LPG prefers the older copper type of plugs rather than the new platinum/iridium ones, but I have no tried them yet.

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^^ Yep, also if the misfire is when you the engine is warm (and running on LPG), chances are you need a hotter plug type as LPG burns hotter than petrol. - Let me guess, you just took what you were given, these will be for running petrol not LPG!

GasFiredDisco said:

chances are you need a hotter plug type as LPG burns hotter than petrol. - Let me guess, you just took what you were given, these will be for running petrol not LPG!

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Hi guys, I have a question, and not alot of Experience with Land Rover/Range Rover motors.

When you mention about the plugs, are there specific ones for Dual Fuel?

Lee1188 said:

Hi guys, I have a question, and not alot of Experience with Land Rover/Range Rover motors.

When you mention about the plugs, are there specific ones for Dual Fuel?

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No, you just want standard copper core plugs, not these fancy platinum or iridium things. And by hotter plugs i mean the ones that disperse heat from the cylinder more effectively.

Higher the number on the plug, the more effective it is at removing heat from the cylinder (well on NGK plugs thats how it works).

I think the first lpg disco we owned had NGK BPR6ES plugs and didnt have any problems with that one!

Cheers, that's helpful to know. Like I say, my experience is not in LR. Thanks buddy.

magnecore are well pricey to be fair i could of had the 8mm blue leads at £112 inc vat but the red ones are 8.5mm inc vat they coming in at £145 ish. Standard copper core leads are fine but once the 12 months is up if they break you got to buy a whole new set however magnecore are 10yr guarantee so they cost £1.61 per lead per yr for 10 yrs which i think is the bollox really cause they will be the last set of leads i ever buy once this V8 is dead its back to the derv for me going to slap a cummins into the disco when the v8 goes up in smoke bring on the deep water, OH YEAH my plugs are the ones that were in the car when i brought it the new plugs will be brought from my lpg installer now.:flame:

..I have bought from Island 4x4 some super dooper 8mm braided 5.5 ohm p/mtr ferromagnetic core leads as a test to see how they do........they have gone on a new engine from day one. I will let you all know when they give up......they were under thirty pounds and were spot on as far as a snug fit goes and have outlasted the new engine which stopped after 127miles.......the story continues....

If the ignition system was designed with high resistance carbon fibre type leads, then it is best to stick with them. Other leads will give a problem sooner or later, might burn the coil out because of too much current.

LPG systems need the rubber tubing replacing from time to time (several years) as the LPG gets contaminated with oil, which rots the pipes, which should be marked as LPG pipe. Cheap kits or cowboy installers use the wrong pipe.

The evaporator / regulator might need to be reconditioned if you have done lots of miles as the gunge as impurities in the LP gas starts to cause problems.

On plugs, higher the number - conducting heat away better, is actually a cooler plug.

Some of the old single point systems need recalibrating / retuning, which you'll need a CO meter to get the mixture right. Rolling road is the best way.

Modern systems - sequential multi-point, with lambda sensors automatically adjust, so aren't a problem.

Other thing might be valve seat recession, where a valve isn't sealing properly - check your compression, just in case. Have you checked your valve clearances? or are they hydraulic lifters?

have fitted me magnecore leads and all is well lack of power has gone, back firing through air box has gone and the mis fire on gas when warm has gone. PHEW an easy fix this time

Check for an air leak around the MAF unit, to change the plugs on the r/h side isn't easy without disturbing it. I had problems with a split in the hose between the MAF and plenum.
MAF sensor is a fussy bugger.