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Discussion Starter #1
I was driving at high altitudes after refueling and when trying to restart my car, it wouldn't start easily.

Now, I need to spray starter fluid to get it running and it occasionally loses power when accelerating.

When the engine warms up, the exhaust begins to pop and doesnt sound normal. Usually when the popping happens, I can visually see the engine stumble and slow down

I have tried spark plugs, spark plug wires, valve cover gaskets and o ring seals, coil pack, fuel filter, and a buddy who is pretty mechanically inclined (rebuilds engines) drove it and said the timing wasnt off (he also pulled the radiator and inspected the belt)

I'm at a loss at this point. The problem came on very dramatically while driving home (about 9000 ft elevation). Basically my car was lunging, stumbling, whatever you wanna call it. I looked like what's portrayed as a shitty car in cartoons that are backfiring and bouncing around lol

Any advise is appreciated. Friend who inspected the timing belt is thinking the heavy load of going uphill in the mountains overheated my cat and caused it to melt down and clog. I had p0420 for a few months and now when I try to drive it its giving me p0171. If it means anything, I cleared p0420 many times and it would take a good 50 miles of driving for it to come back on but for the past couple months I've just been driving with it on

Also head gaskets are relatively new so I don't think that's an issue but who knows ?‍♂

Thankss y'all
 

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Do you know what has been causing the P0420? My car, 230K, had that code as symptom of misfires, too much unburnt fuel going through the exhaust. With everything you've checked, it sounds like time to go through the emissions systems. PCV diaphragm, O2 sensors, MAF and MAP sensors. Maybe fuel pump or injectors.
 

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Not really unfortunately. I'm assuming it was a bad o2 sensor. I called a mechanic when it first came on in July and he said it's nothing to worry about since I just had emissions passed in June. Should I try replacing an o2 sensor before the entire cat? I'm told cats going bad on this gen outback is a common problem and they show symptoms I'm experiencing. Just never thought it could come like someone just flicked a switch
 

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It does sound like it might be a partially plugged cat. If you remove the cat section (two cats in series), you can look into each end and see if there is any evidence of melting or clogging of the honey comb that is visible. I had a Forester that my son ran over something that hit the cat hard and broke up the honey comb. The car would start and run ok for the first few minutes but would drastically lose power as it came up to temperature.
 

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Just bump - w/your hand, not a rock in the road - your CC's to see if their contents is loose.

But yeah, sounds like you may have fried your cats by ignoring the P0420...or they were bad already, and finally clogged your exhaust.

If it were the O2 sensors it would likely run poorly once warm - not when cold, too. Technically, the O2 sensors don't do anything 'til the car reaches operating temp (which is Closed Loop) and referencing the O2 sensors. When cold, car is in Open Loop and just running off the ECU's programming.

If you confirm it's a clogged cat(s), Find a Subaru part-out nearby and just buy another used exhaust, if possible. A Legacy should also fit - but might need different hangers.
 

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Discussion Starter #6
Just bump - w/your hand, not a rock in the road - your CC's to see if their contents is loose.

But yeah, sounds like you may have fried your cats by ignoring the P0420...or they were bad already, and finally clogged your exhaust.

If it were the O2 sensors it would likely run poorly once warm - not when cold, too. Technically, the O2 sensors don't do anything 'til the car reaches operating temp (which is Closed Loop) and referencing the O2 sensors. When cold, car is in Open Loop and just running off the ECU's programming.

If you confirm it's a clogged cat(s), Find a Subaru part-out nearby and just buy another used exhaust, if possible. A Legacy should also fit - but might need different hangers.
Do you know if a 2005 legacy would fit?
 

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I doubt it. 2005+ was Gen3 and Subaru went to a dual exhaust, and a new body. '00-'04 OB and Legacy. Wagon, and maybe Sedan, are likely it.
 

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Discussion Starter #8
Cool I'm gonna get looking for a used one. If a cat clogs mid driving can it cause really dramatic lunging and blinking cel?
 

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Front o2 sensor, swap it for a new denso, . That brand matches subaru spec, and maybe the Subaru maker today. I had such problems 2× on my h4 car, swapping the front o2 solved it. Same original car converter with 130,000 miles and counting.
 

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Cool I'm gonna get looking for a used one. If a cat clogs mid driving can it cause really dramatic lunging and blinking cel?
Hey man I’m not a mechanic and I don’t want you to spend money you shouldn’t so you need to do some due diligence and make sure that it’s actually the exhaust. Refer to what people post it up above about maybe pulling the exhaust off and seeing if it runs better or see what people do online. Just don’t go replace it and expect it to be fixed.
 

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Technically, the O2 sensors don't do anything 'til the car reaches operating temp (which is Closed Loop) and referencing the O2 sensors. When cold, car is in Open Loop and just running off the ECU's programming.
But is shouldn't wait until the "car reaches operating temperature". The A/F and O2 sensor heaters take a bit of time to bring the sensor itself up to temperature, and at that point, the ECM switches over to closed loop

If the car was parked for some time with outside temps above freezing, it would take between 15 and 30 seconds. If the ambient temperature is below freezing, it could take up to 60 seconds, and when well below freezing, perhaps 90 seconds. But, normally, it is clearly before the engine reaches its normal operating temperature.

The status of the fueling system, i.e., open loop and closed loop, can be monitored with most live-data scanners.
 
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