Have just changed the spark plugs in my MY94 WRX RA to NGK PFR6B's
And looked on the SIDC F.A.Q and it said 1.0mm for gap but in a UK workshop manual it says 0.8mm so i have set them at 0.9mm.

Now when i go down the road its fine until i floor it and it reaches full boost when POP BANG POP BANG BANG out the exhaust.
It shakes the about too, (DONT MIND THE POPPING AND BANGING) but something is not right and am worried about if it doing any damage...

Does not do it any other time but only at full boost. The boost gauge waives around but the Check engine line does not light up.

Should i put the Spark Gap back to 0.8mm where the old ones were?

ANY IDEAS
Thanks in advance
Scott

[Edited by scoootie5 - 2/17/2002 6:14:27 PM]

 

Scott

The plug change is a bi*ch to do as you found out, however I would change the gap to what the FAQ site says:

Spark plugs NGK PFR6G/PFR6B
Spark plug gap 1.0 to 1.1mm

It may be that the gap is too small for the spark to fully develop and therefore the air/fuel charge in the cylinder is not being burnt fully.

The unburnt fuel is then re ignited down stream in the extremely hot exhaust when a new charge of air is available, near the end of the muffler.

Hope this helps

It may be possible that one of the plugs is missfiring also causing the same problem.

Are these "NEW" plugs or just regapped older ones?

Is this the only thing that you have done to the car since it was last working well?

If so I would be more inclined to think that it is the gaping.

"Should i put the Spark Gap back to 0.8mm where the old
ones were?"

Were the old ones the same PFR6GB set to 0.8mm

When checking plug gaps, the correct way is to use ONLY wire gauges, though many of us are using the slider style gapping tools. These flat or feeler gauge style gauges do not accurately measure true width of spark plug gap.

Also see this link:

http://www.extrememotorsports.com/plugfaq.htm

Chow

 

Thanks for the reply,

They are Brand new and are replacing exactly the same NGK PFR6B's
The old ones were 0.8mm i have checked them and did not have the same problem before.

I haven't done anything else otherthan changing the plugs.

Wierd one this did not know that such a small alteration in gap could be such a pain.

Thanks Again
Scott

 

Plug gaps are TOO BIG, you are blowing out the spark with boost, correct gaps for the turbo engine are 0.7mm.Set at that. If you still have trouble then your coil packs are at fault. Early cars are VERY sensitive to plug gap

 

Could be your plug coil packs are past ther sell by date and the slightly larger gap is too much for the spark to jump.Try re gapping down to 0.6mm - if the problem goes then it is probably the coils.

Steve

 

I have just read the link Lizzard left for me and by the sounds of it i am having a BLOWING OUT problem.

I shall put it back to 0.8mm as it was.

Thanks to you both for finding the time to reply.

Scott

 

Now back at 0.8mm and all is well again.

Next time i will leave alone.

Thanks again

Scott

 

Just for your information almost all plugs come pre gapped so they are ready to drop straight in.

 

I thought pregapped plugs were always set at about 1.1mm.

 

Scoty

Not to confuse the issue too much on my previous post, I ommited to say what Bob Rawle stated, that indeed too BIG a gap can cause the spark flame to be extinguished.

The resulting backfire and flames is in fact the gas being ignited down stream in the exhaust.

This just goes to show that the problem can be caused by two different aspects of plug gapping.

The NGK plugs do in fact come pre gapped, however you should always still check them before installing them to ensure accuracy.

Sorry about the confusion!! All's well that ends well!!

 

See this link concerning spark plug gaps from an NGK engineer.

Hope it explains the nuances between too large and too small a plug gap size.

http://www.extrememotorsports.com/plugfaq.htm

Cheers

 

It's okay that was my first though that the gap was to small and unburnt fuel was going down the exhaust, until i read your link.

Thanks Again for your trouble its all running puurfect now.

Scott

[Edited by scoootie5 - 2/18/2002 4:17:43 PM]

 

You're Welcome!!

 

No not all plugs are 1.1mm only the ones that have 11 in the plug codes, which would be the minority of plugs.

Dan