OK - what's the likely suspect? Plugs, wires or coil"

 

one or multiple?

 

No apparent hesitation or vibration (suspecting plugs first - changing to new NGKs tomorrow but the question is whether this code will show for "other strange things")

 

Suppose I should run a compression check too...

Sorry I forgot what model and year soob this is?

 

Most common soob misfire causes.

a. non-NGK spark plugs

b. non-OEM or Magnecor spark plug wires

c. old/aged/in need of replacement spark plugs or wires

d. coil pack cracking/carbon tracing

e. oil collecting in spark plug tube (for soob engines where the spark plug tubes penetrate the valve cover).

 

less common but can be

f. one or more valves not closing completely (i.e. valve lash in need of adjustment - post '96 engines only as prior to that hydraulic lash adjusters HLA's were used). Can also happen if cylinder heads are severely carboned up.

g. timing off/jumped tooth/etc

 

of course there are other things too.

Misfire codes (P0303 in your case) are set when the ECU detects that the engine slows slightly as a particular cylinder fires, because that cylinder isn't producing full power. While ignition problems are often the cause, they certainly aren't the only possibility.

 

So yes, change the plugs, and do a compression check while they're out. If getting platinum plugs, be sure to buy the "double" type.

also easy thing to check is that the connectors for the fuel injectors are in the correct spots......

97 Impreza L Wagon.

 

I've already bought the NGK v-notch plugs, and WILL buy OEM wires (which aircraft-engineer says I don't need to spend for) because everyone on the board is adamant the OEM wires are the only good choice.

 

It's not running rough, and I was headed downhill when the light came on (with the brakes on or running under its own weight). After the light came on I went to the nearest Schuck's (2 miles) with no trouble, back to the freeway and a 4 mile flat run, and then climbed a pretty steep 2 mile hill (still freeway) at 55-60 MPH with no trouble (as far as I can tell - until we get the bearing(s) replaced in the back the growl is louder than the engine).

 

The Schucks guy checked the wires after I did, and said he might have felt a bit of loose play on the rear driver's side wire.

 

I wonder if Subaru of Puyallup checked all the wires a week ago and one wiggled loose? It's been one week exactly since they diagnosed the oil leak/bearing problems. They mentioned I needed new plugs, didn't mention wires at all.

ho-hum - pulled out all the old plugs - would you believe gapped at .080 and still running? Cleared code and didn't come back on again

 

The more I fix, the more I believe that the blond who owned it before was an utter DINGBAT (and I'm not even sure about the timing belt 80,000 ago claim either with cam seals leaking - that gets done this week-end along with the pax rear bearing)

ho-hum - pulled out all the old plugs - would you believe gapped at .080 and still running?[...]

Gee, only nearly double the spec.