Stumped on my highschool daughters first car - 2008 Legacy can't go up hills and has no power

[idosubaru]

Engine starts and idles fine, can't tell anything is wrong until you go to drive it. It's severely underpowered.  Floor it and it very slowly accelerates, sometimes can get up to 40 mph on flat or downhill.  It won't even make it up a steep mountain, so it's undrivable around here. New headgaskets, timing belt, and compression tested fine so I assume the timing marks are still good, but Ill check them tomorrow.  Drove fine for 3-4 months after the HG then gradually got worse over a week before it became undrivable.

The oil had significant coolant/water mixed in with the oil before I did the HG's - could the valve control solenoids be damaged by that? 

P0038 front O2 sensor code - car does the same thing with the sensor plugged in or unplugged.  Will these run without a front O2 plugged in?  Maybe the 02 sensor is bad.  It has a 4 wire Bosch O2 sensor with the old plug spliced on - does anyone know how to verify the wires are correct?

It had a cylinder 3 and multiple cylinder misfires - I replaced the plugs and wires with subaru issued goods, and the codes for those went away - but the CEL did flash last night on a test drive then quit...so maybe it's still doing it intermittently. 

Any suggestions.....

[brus brother]

Possibly clogged cat converter(s)? Broken bit's of the honeycomb will follow gravity and clog the exhaust when car is heading up hill. The noise will startle the neighbors but if you can disconnect the cat(s) and test drive, that will help in diagnosing this issue.

Buddy had this issue and just emptied the broken bits and drove on.

Edited yesterday at 12:49 AM by brus brother

[ronemus]

I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor.  There are lots of possibilities for those symptoms.

It will run without the O2 sensor, but it does so in limp home mode which would be as you describe - I would start with a new O2 sensor.  Rock Auto sells Denso Front O2 Sensor which is GTG.  How is fuel mileage?  If the A/F ratio is off the mileage will suffer.

[idosubaru]

2 hours ago, brus brother said:

Possibly clogged cat converter(s)? Broken bit's of the honeycomb will follow gravity and clog the exhaust when car is heading up hill. The noise will startle the neighbors but if you can disconnect the cat(s) and test drive, that will help in diagnosing this issue.

Buddy had this issue and just emptied the broken bits and drove on.

Oh wow my good sir, wasn't considering the exhaust at all. That would be awesome. 

Aye aye captain - I rammed one out of an XT6 20+ years ago. 

 

16 minutes ago, ronemus said:

I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor.  There are lots of possibilities for those symptoms.

It will run without the O2 sensor, but it does so in limp home mode which would be as you describe - I would start with a new O2 sensor.  Rock Auto sells Denso Front O2 Sensor which is GTG.  How is fuel mileage?  If the A/F ratio is off the mileage will suffer.

It's not drivable enough to accrue miles and calculate gas mileage.   Yeah this is a new sensor but it's the style that comes with bare leads you splice the old connector onto - and I do'nt trust that it's wired properly.  I'll check those. 

[idosubaru]

Doesn't seem to be the oxygen sensor.  I'll try disconnecting the exhaust in the morning.

[forester2002s]

Could be a partially-clogged fuel filter.

Put in a new one, and see if it makes any difference.

[idosubaru]

10 hours ago, ronemus said:

I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor.  There are lots of possibilities for those symptoms.

What  year/model engine and did you have check engine lights in those cases? Max 4,000 RPM with no power for hills but otherwise drives without hiccup or stalling is oddly specific, I doubt your symptoms were identical. It would be drivable on flat land, but can't get up hills. 

[idosubaru]

6 hours ago, forester2002s said:

Could be a partially-clogged fuel filter.

Put in a new one, and see if it makes any difference.

2005-2009 doesn't have a fuel filter, or it's "in the fuel tank".  

[idosubaru]

Cat converter - seems fine, disconnected exhaust and still runs just as bad. 
Fuel filter is in the tank, can't replace - i'll have to pressure test or pull the fuel line and see how well is sprays out
 

Ill get a new oxygen sensor later.

[idosubaru]

14 hours ago, brus brother said:

Possibly clogged cat converter(s)?

You were right! Thanks man!  Now...this newer 05-09 stuff has the curved catalytic converters right by the engine, they're going to be much harder to gut....

[idosubaru]

1 hour ago, idosubaru said:

Cat converter - seems fine, disconnected exhaust and still runs just as bad. 

Converter ended up being the problem - just took a minute to warm up and relearn I guess,  Runs perfect without the exhaust connected