Warning Brisk LPG spark plugs
 

I recently had a car come in for service with a very bad misfire while under any load. It was so bad the car was almost undriveable. With all other components changed including new coil packs the only possible cause had to be the special LPG plugs fitted by the owner.

After removing the Brisk silver LPG spark plugs that were almost new (only a couple of thousand miles) and fitting a set of NGK copper core plugs the misfire had almost totaly disapeared, with a bit of remapping solved.

Looking at the plugs you can see they have no hope of working well with LPG. LPG likes a single spark path and the Brisk plugs have 4. You could see on each plug that 1 path was black, the 2 paths to the side had a thin black line and the other path was totaly clean. The sparks were not able to track each path at all with only 1 making a resonable spark 2 intermitant and the other almost not at all.

My advice is to save yourself some money and avoid these plugs especialy with turbo engines.

The best plugs to have are a simple basic single electrode copper core plug.

Dai's just converted our 3.2 XC90 and the plugs were the original iridium coated OEM Ford parts with 45,000 miles on them... They were playing up within 500 miles of the conversion so we've now gone with some standard NGK's at around £4 each!

I changed them myself whilst chatting on the phone to one of my mates and still did the whole lot in 20 minutes - no running problems since :-)

NGK has a technical support department here in the UK and they are, as you'd expect, very knowledgable and very helpful too. Full marks to NGK (and Dai on our conversion).

single prongs should be used on any application to be honest regardless of LPG converted or not.

extra prongs just make them last longer

The extra prongs are not there to increase life.

The idea is that they should give a stronger and broader spark. The effect of the stronger spark can give a small increase in power upto 2% and improved MPG upto 2%.

The problem is LPG is not conductive like petrol so the ignition system is strained and more power is needed to create a spark. Under these conditions the spark will not travel to each prong as there is not enough power there and the spark will only take the easy path. The end result is uneven sparking and misfiring.

NGK are helpfull and will advise on the best plug for your engine running on LPG.

The idea of multi prong plugs is indeed ONLY long life , basic electronics say the spark will always take the easiest path , it is impossible for the plug to have multi sparks on each prong at the same time unless it is fed with huge amounts of HT energy..
what happens is that the spark takes the path of least resistance which is the prong with the shortest gap , as this wears, the gap gets wider and eventualy the next unused prong is the easiest path and that one starts to get used , and likewise until that wears and the third prong starts to get used etc , that is how volvo plugs last 72000 miles ..
You may choose your particular plugs that work right with your LPG, however if you use it on petrol often you will find the genuine volvo plugs give the best performance of all . Volvo ignition systems are and always have been very powerful and really should cope with lpg , they always did fine in the 1980s-1990's-2000's what's changed ? .. I guess genuine volvo plugs were not tried first on this problematic engine ..

The issue is purely down to spark plugs. As already said muti prong plugs are problematic and should be avoided with LPG.

Most of the Volvo plugs are still single electrode items but the tip material has been changed to platinum or iridium depending on age/engine. LPG eats platinum spark plugs and they will last from a few hundred to a few thousand miles. Iridium plugs are fine with LPG but last no longer than a basic copper core plug.

Volvo petrol engine plugs have simplified now to single electrode platinum tipped for turbo engines and 3 prong multi electrode for non turbo and change intervals are 75000 miles after 2007 ..

my Volvo runs happily on single electrode plugs

my other car which is a VW passat 1.8 Turbo, I can't seem to find anyone who does single electrode plugs for them, I've got fitted Denso triple electrode and you get a slight misfire on high boost

I had thought of buying some of those brisk plugs... I'll save my money

Give NGK technical a call and they will be able to tell you what plugs will work in that engine with LPG. I used to have the plug number for them as the Audi/VW turbo used to be a common conversion and the plugs had to be changed. There is a single electrode plug that fits correctly.

cheers
I'll see if I can find a phone number on their website