I have a 1995 WRX STI RA and have serviced it, changing all the usual parts so i thought to my self i might as well change the spark plugs then i will know that everything has been changed (even though there was no problem with the old ones). When i went into my local car shop the plugs they gave me NGK R PFR6B which was shown in their guide, i also checked the NGK website which backed this up. Problem is that i fitted them the other day and now between 4,000 and 5,000 revs it plays up almost backfiring in every gear under load. The plugs that came out were NOT NGK R PFR6B but they were NGK R PFR6G and when i checked the gapping the new plugs 6B's were 0.10mm more closed than the 6G's that came out of the car.
Should the fact that my car is an imported STI RA which is used for competition use be different to the standard WRX stated on the NGK website and can anyone tell me what the difference is between the PFR6B and PFR6G. I will probably have to go and buy some PFR6G's to stop this problem but wanted to know why this was happening?

Thanks Chris

 

The correct plugs are PFR 6 B. Many people use PFR 7 B, especially if they have done a few mods. I cannot tell you how a 6 B compares to a 6 G but the website at NGK may have this info or ask NGK.
On an O/E engine, run .7mm gap. With higher boost this can be reduced to .5 mm.
It may be a problem other than plugs and gaps, coil pack on its way out for instance.

 

think the difference between the plugs is the 6bs are platinum and the 6g are iridium. you may have damaged a coil pack when removing the old plufs

 

both 6g and b are the same plug, from previous research the 'g' is simply the factory fit option...............and the 'b' the generally available version

 

that hapend to me some how i cracked 1 u had to look really hard i get a new 1 and it was ok

 

Iridiums have a totally different code. As Alyn has said, the 6b or 6g will do exactly the same job. You either have a duff plug (rare) or you need to look elsewhere for the problem.
JohnD

 

Thanks for your help. I decided to put the old plugs back to see if the problem went away (which would mean it was the plugs). You boys were right the problem was still there and on inspection a coil pack was cracked so looks like i will have to replace them. Does anyone know where the best place to buy them from, price wise?

Thanks chris.

 

API are the cheapest I have found for genuine coil packs. Next day delivery as well

 

so did this work ? ive got the same thing with mycar api just quotid me £198for 4


but do you need to get all 4 ?

 

i went for new plugs and when the coil packs were removed two were cracked and i was advised to change all four, which makes sence because if you leave an old one in it could go at any time and cause the same problem again. i was also told it was best to change the oil if a coil pack hadnt been working for a while as some petrol can get into the oil, and when i did change the oil it did smell strongly of petrol