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Discussion Starter #1
Hello,

I recently purchased a 97' Legacy Outback Wagon with the 5mt. The car had some transmission problems and a check engine light for O2 sensors. I have already completely replaced the clutch, oil separator plate, and such in the transmission. New O2 sensors as well. I put everything back together and the car has been running great until yesterday. On about a 30 minute drive I noticed some hesitation when accelerating in certain gears and then the check engine light came on.

Had the codes read and its showing misfires in all cylinders. So far I have checked all of the vacuum lines that I can find, I pulled the MAF and it looks brand new inside. The previous owner had a complete tune up done on the car towards the end of 2017. Plugs, wires, fuel injectors service, timing belt, water pump, head gasket, and valve cover gaskets. All of that was done at an actual shop as well.

Things that I think may be issues, but I'm not entirely sure about:
Needs a new air filter for sure
Battery is somewhat old: Also the battery did die yesterday while having the windows tinted with the doors open.
EGR looks original
Not sure about the history of the fuel pump but the fuel level gauge does bind on the instrument cluster and doesn't move down at a steady pace.
Knock Sensor?

Like I said there isnt anthing particularly jumping out at me as to what the issue may be but considering its coding for all cylinders Its harder to narrow down exactly whats going on without replacing everything. I do plan to replace the battery and get some new power and ground wires, as well as pick up a new air filter.
 

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Read the check engine light see if there's any stored codes.

All 4 cylinders - i would check the timing marks and components right away. See if the tensioner is loose and marks are properly lined up.

I'd like to make sure they are NGK plugs and wires or Subaru...but that's rarely going to cause 4 misfires. There aren't too many things that should cause misfires in every cylinder so I wouldn't start guessing too soon.

Did you buy it with issues or they exhibited soon after purchase?
 

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@idosubaru
I have all of the paperwork from the shop that did all of the work back in 2017. The plugs are indeed NGK platinum. The coil pack and plug wires are also new although not ngk wires. The shop also did the timing belt so i would hope that they set it up right. Its only been 15k miles since they did the service.

And the only code it had when i bought it was the o2 sensors and just yesterday registered the misfires. It honestly drives great. there is a little hesistation at lower rpm. Im doing a fuel pressure check now just to see if theres so sort of pressure issue.
 

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misfires on all cylinders:

o2 sensors that are not Denso. (NGK are probably great too, but more expensive.
other labels do not give the ECU the exact data as it expects, won't make a o2 sensor code but still suck = misfires). inspect wires on the o2 sensors too,

coil pack that is not NGK (or stamped "subaru" on front),

plug wires that are not NGK. (I think subaru is selling bedlen? now, but odd labels hit or miss in aftermarket,
but NGK and known great.)

engine grounds. plug wires that are all a little loose,
...look for rodent chewing on engine grounds wires/ o2 sensor wires.

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and chuck that xxxx for a new OEM. (edit: had o2 sensor, should have typed PCV)
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if you think you ever need a alternator: subaru had a recall back in the day for these. they made lots of them: $75 buys the real subaru rounded up from the warehouse, and not some guaranteed half fixed junk reman used in a ford, a toyota, and a dodge 3x before it gets in your car.
 

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Discussion Starter #5
@eagleeye

Thanks for the info. Im leaning more towards the o2 sensors because they are aftermarket. The plug wires and coil pack are too but the motor sounds great and runs well. I do plan on upgrading the power and ground wires with some nice ones just for a better circuit.
 

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@eagleeye

Thanks for the info. Im leaning more towards the o2 sensors because they are aftermarket. The plug wires and coil pack are too but the motor sounds great and runs well. I do plan on upgrading the power and ground wires with some nice ones just for a better circuit.
what are they? Denso or NGK maybe the subaru maker today.

Denso I know matches the subaru spec, is easy to buy and cheap.
(parts store counters like to screw people on plugs/wires / o2 sensors / wipers, as they have you and presume you need such things .
vs. say Rock Auto).
 

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They are kwiksen. They had decent reviews and were around $50 for both, but thats why i think they may be the problem
so,... we need to send the subaru 🚙 police out to rescue your car that you are abusing with junk parts.;)
 

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Discussion Starter #9
Haha. I just spent a good deal on replacing the clutch and trans parts and some other stuff so wasnt looking to spend $150 on o2 sensors right now
 

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Haha. I just spent a good deal on replacing the clutch and trans parts and some other stuff so wasnt looking to spend $150 on o2 sensors right now
on these the front one does all the talking to the ECU, and makes the problems,

rear one gives a p0420 code when the data from the 2 is compared showing cat inefficiency. (on a 2003 and newer might do more, and on a 2005 and newer does do more).

I have had spacers on my rear o2 sensor for a while. (the subaru pipe design on a EJ251 like my H4 2002 is kind of odd, and might make for a easier p0420 even if there is nothing wrong).

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I have replaced the front one 2 x due to minor misfires and spazzy weirdness though. eventually you might get to a p013x type code if things actually get bad enough to pop and hold a code. (misfires usually don't save)

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problem with keeping things as they are: degrading ride quality, maybe some bucking when a truck is going to kill you. possibly ruining a cat converter.
 

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This is my first subaru so i dont know all the ins and outs. The exhaust on my car is the only thing what so ever with rust on it. I cant find a quality replacement either for my outback. I dont know if an exhaust leak could cause the o2 sensor to be off and if that could be part of the problem.
 

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This is my first subaru so i dont know all the ins and outs. The exhaust on my car is the only thing what so ever with rust on it. I cant find a quality replacement either for my outback. I dont know if an exhaust leak could cause the o2 sensor to be off and if that could be part of the problem.
if it is up front before the o2 sensors yes.

what you get is the outside air mixing in with what the sensors think is 100% engine exhaust.
so typically a p0420 code for "too much oxygen" in what the rear sensor shows as a bad cat converter.
(as it can't burn up the regular engine exhaust plus the extra c2 getting sucked into the hole before the cat).

other spazzy behavior though happens from the front one.


both my 2002 cars had rusted apart flanges between the mid-pipe and the muffler inlet. and a nice new union weld in where they use to bolt together. (I mean like welded together for 10 years).

so where is the holes. ?
 

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1. clear the codes and see if they come back
2. if you're constantly getting the codes then you could test your O2 sensors to see what they're doing.

I would want to know the brand of the wires and see if the timing belt tensioner is loose. I've seen cheap aftermarket wires cause misfires...though all 4 would be somewhat of a surprise.
 
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