P0301, sometimes also P0302, Check Engine Light on at high RPM

[BlueSoob]

1997 Outback 2.5 5mt

Misfire code - I've changed plugs and plug wires... wires twice.  Ignition coil..    Never hesitates when starting, never stumbles..  But finally I've noticed a pattern... at about 78-84 mph, at about 3500-4000 rpm, driving even just slightly uphill, the check engine light comes on....    I'm stumped.   Help.

[Fairtax4me]

Does it ever do that in lower gears at the same engine speed?

 

What kind of plugs are in it?

[BlueSoob]

NGK plugs and wires now,   I've not been able to get the light to come on in lower gears at same RPM.  I tried to get it to come on when on level freeway... tried four times... wouldn't come on... until I was heading up and over a pass.

[Fairtax4me]

How many miles on it?

How old are the O2 sensors?

 

When the light comes do you actually feel it stumble when it misfires?

[BlueSoob]

No stumble, no hesitation when it comes on..  The light will flash at me 3-10 times.  I reset the light and it won't come on until the same conditions happen.  

No idea how old the O2 are....  it has 308,000 on it.   I have all the repair records since almost new.... I know a lot... a lot of work was done between 140-160k  (I bought it at 200k)

https://www.facebook.com/35305adventure

[johnceggleston]

 

I know a lot... a lot of work was done between 140-160k  (I bought it at 200k)

well the good news is,

the car does not owe you anything.

you have gotten your money's worth.

 

a compression test might be a good starting place.

or just check the timing, it may have just humped a tooth.

 

 

at 300k,

valve clearance comes to mind.

as does timing

plug wires unless yours are very, very, high quality.

[jmoss5723]

I've had this happen twice. Once in my Forester and once in my brother's Impreza RS. Exactly as you've described it, except as time went on, it got worse and the cars would start bucking with the misfires.

 

In both cases it was from oil leaking past the seals on the valve cover and into the spark plug tubes. Check the rubber boots for your spark plugs for oil.

[ccrinc]

You have come across the dreaded "ghost code" which eventually got into damn near every '97-'98 Outback with a manual transmission.  This has been around for years, I've known dozens of people who have experienced it (myself included on my '97 Outback Limited), Subaru knew about it and never addressed it except to charge $50 a pop to "reset" the ECU.

 

There is NO known cure.  Luckily, it is not dangerous or deadly, just annoying.

 

Scenario: you reset the ECU, the light goes off and stays off.  You can drive around town (i.e., under 60mph) for months and it won't come back on.  The very first time you go over 75mph for 3 mins. or more, it comes back on.  (Here in CO, it will come on at 65mph: I think the altitude may affect it.)  Car runs great, no problems but that stupid light.  Amiright?

 

You can Google this: pages and pages of results come up with the identical issue.  It's like the car won't do it until you change one little thing, anything, and then suddenly, you can't get rid of it.  I have a customer at Faulkner Subaru in Harrisburg.  A few years back, we both had identical cars and were laughing about this issue.  The one thing I don't like about it that when your CEL is on constantly, you have no way of knowing if it set a new, real and meaningful code.  Some people I've known have just put black electrical tape over it. 

 

Emily