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P0303 and P0304 after engine install - spark plugs?

1901 2
So I pulled the engine, replaced clutch, head gaskets, valve cover gaskets, oil pump gasket, separator plate and just about anything else that could leak oil. Everything went back together perfectly and except for a huge pain in getting the coolant to burp, the car is now running perfect.

I took it out on its first "long" drive yesterday, about 30 miles, and at the turn around point it threw P0303 and 0304. Took it into Napa and read the codes - cylinder misfire on 3 & 4 and had them clear the codes, which have not yet come back.

My number one suspicion is the spark plugs. I did replace them but I think I did something stupid and gapped them to .44, on a platinum plug (came out of the box at ~.35. Just a brain fart at 10pm. My suspicion is that I scratched or bent the plug and will be replacing them.

Is there a concensus on what is the best plugs for a 99 OBW? I know NGKs are the way to go, but I think there were 4 options.
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Gallery Ninja, ,
2004 Outback "Bluebaru" & 2005 Outback XT
5,270 Posts
From what I've gathered, the misfire codes could be:

1. Bad Spark Plug Wires (make sure to seat them well on both ends)
2. Bad ground on engine. (add ground wires)
3. Exhaust leak at header / pipe.
4. O2 sensor failure.
5. Valve sealing issues. (test your compression)

There's seem to be a number of reasons these cars get misfire codes on cylinders 3 & 4. I've still not solved mine yet.

34 Posts
Discussion Starter · #3 ·
Thanks for the response. Put about 600 miles on it since the codes popped and they have not popped again.

I am still going to put in some new plugs and wires but I suspect it was a hicup after the engine removal/install.
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