I have a '96 outback with the 2.2L and 5-speed.

 

It started misfiring under load and finally threw the P0302 CODE.  It happened right by the parts store so I just cleared the code and it didn't come back right away.  Still misfiring under load but not bad.  I looked under the hood after dark and there was no arcing or sparking of the plug wires even while misting water around the coil.

 

After a couple of days the code came back.  It was finally the weekend so I had time to pull the plugs.  They all looked like the text book picture of what a perfectly firing plug should look like but were hugely over gapped, probably near .060".  I regapped them and put them back in to see what would happen.

 

That made a big difference.  It was running way better.  It still felt like I could make it misfire or stumble or whatever by intentionally lugging it in too high a gear, so on the way home from work yesterday I bought new NGK's and went home to change them.

 

Of course since I was in a hurry the first thing that happened was that the plug wire pulled out of one of the spark plug terminals.  I didn't have time to go buy new plug wires so I repaired it the best I could with a screwdriver and needle nose pliers.  I'm going to order up a new set of NGK wires this morning.

 

NOW to my main point.  It wasn't until after I had a couple of the plugs in that I noticed I had purchased BKR5E11 plugs.  The plugs that came out were BKR6E11.  I just put them in, put everything back together and took it for a quick run on the highway.  It ran AWESOME.  No sign of misfire or stumbing under load.

 

So this morning I am doing some research and I get conflicting information on whether the 5 or 6 is the right plug to use.  It looks like it probably should have been the 6.  Interesting that if I go to the NGK website and punch in the 2.2L for the '96 outback it tells me to use the 6, but if I punch in the 2.5L it tells me to use the 5.  I also found this part number decoder which I thought was pretty cool:

 

http://www.ngksparkplugs.com/docs/tech/design_symbols_plugs.pdf

 

So I am thinking that I probably should have went with the 6, especially since the 6's that I took out looked like the text book picture of what a plug should after around 100K miles.  Do the experts agree that I should be using the 6's?

 

Is running with the hotter 5 plug really that big of a deal?  Do the experts think I should eat the $10 bucks and buy a new set of 6's to go with the new plug wires?  Or should I not worry about it and just go with the 5's?

 

Thanks to all who bothered to read this far.  I have a tendency to write novels.  And I did do a search first.

 

Either should be fine.  Not that much of a difference.  Make sure you get Subaru or NGK plug wires.

If it dont say NGK throw it away !!!

As long as you do not run on Propane (LPG) the 5 should not give any problems. At next change check how the colour looks like.

No harm done running the 5 plug in the 2.2.

 

But you do have a point, its interesting that they spec. the 5 for the higher compression 2.5 engine. Seems to go against conventional wisdom, but I'm sure Subaru had a good reason to use a plug with that heat range.