dubtavious

I took out the MAF and one side of the red tipped sensor piece had a decent amount of gunk on it. Do MAFs typically have a bit of dirt on them or are they usually clean?

I cleaned it up and put it back in.

So, I had the work done. One valve was replaced the others got resurfaced. They did the timing belt, gaskets, the small turbo hose, etc. (It's all listed on the work order).

Drove it for about a week and it all felt pretty good. MPG seemed a bit on the low side, but I've done zero highway driving (sitting at 21.6 MPG over the last 150 miles).

Anyway, today the check engine came back on with code P0171. Super frustrating.

Possible that they missed tightening something up when they put it all back together? Front 02 sensor is fairly new. Only about 18 months old.

Popped the hood to see if there was anything obvious going on and it felt like there was air flowing up from the left side of the engine, so maybe an exhaust leak or a leak around the air filter? I can't say for sure, but I feel as though anytime I've looked at the engine while it was running before today and I never felt any significant amount of air moving on the left side of the engine.

do you know about BTSSM? if you have an Android phone and this app and an appropriate obd2 dongle, you can then log the ECU parameters. This way, you will know if you are actually misfiring while driving. It will report misfires per cylinder. This happened to me once when I swapped injectors and one of them was not sitting properly. It dumped quite an amount of fuel in the cylinder while I was driving and was misfiring intermittently. When I got home the up pipe was glowing red

I do have an android phone. Are one of these dongles available on Amazon? May as well have one on hand.

Here is the theory (or at least how I understand it):

case 1: assume you have a slightly cracked ringland. In this case, it is most likely to have a rough idle when cold instead of warm; cause when fully warmed up, the rings expand a little and may seal the crack and bump compression back to almost normal or acceptable level.

case 2: assume your ringlands are fine but you have a tight exhaust valve. In this situation, the rough idle may be more pronounced when fully warmed up. That is because the valve stem expands a little with a warmed up engine. Combine this with zero clearance, you then end up with a valve which cannot close. Result, poor compression ---> rough warm idle.

case 3: burnt valve. I am not too familiar with that case as it has never happened to me. But I would surmise that you would have both a warm and cold idle since a burnt valve would either be cracked or missing some pieces. This means that poor compression is always present regardless of engine temp.

Oh, gotcha. That's a great explanation. Going by that I'd say it's either 2 or 3. Idle definitely wasn't less pronounced when warm. It was either the same or perhaps a bit more pronounced.

Terrible MPG would be a symptom of both 2 and 3, yes? As I said earlier I haven't noticed any changes in oil consumption which from what I understand would be indicative of case 1.

does there happen to be a subie performance shop a place you can drive or call and talk to them? I know this place works on them but, a dedicated performance shop that is know for their work would be my choice.

Not that I know of. I did call the other Subaru specialist in the area and asked them if they would have done the leakdown test and if it was a bad sign that the other place didn't. They said they would have done the test. They basically made the same points as many in this thread. Unfortunately they're at least a 20-25 minute drive away and I'm mortified of doing more damage to the car.

Just went for a short drive. Idle was rough but not crazy bad. Was the same when I started it, after two minutes, and after a ten minute trip into town. Check engine light popped back on. MPG still seems ridiculously low.

At this point, I going to just bite the bullet and drop it off for the work.

How is the cold idle? Like you start the car, drive it for 2mn or less, then let it idle (still not fully warmed up yet). Does she run rough as well?

I'll check that soon as I need to take a quick trip.

What's the thought here? If it was rough at idle, but smoothed out after a short drive what would that mean?

Hard for me to judge the idle because the car has been running rough for a few weeks due to a hole in the centerpipe which was replaced/fixed today. When I pulled out of the shop the car was chugging a bit and same at home when I parked it 10 minutes later. The car's MPG is total crap now.

So biggest downside to not doing a leakdown test is they get in there and they're light 'oh shit you need a shortblock'? He was pretty convinced it wouldn't require that. Oil consumption seems normal. Haven't noticed any changes there.

With the holidays etc. I'm on a pretty decent time crunch and def don't want to be off the road extending into the new year. They strongly, strongly suggested driving the car only short distances at most, so getting to another garage that can do a leakdown test might require a 20 minute drive each way. I live in the sticks, so being without transport is a bit of a shit show.

Really appreciate the all your answers, guys.

Huh, I just spoke with them again and he said they never do leakdown tests and he was fairly certain it was a burnt valve-- based on the compression test, symptoms, and experience (these guys wrench on Subarus all day every day and I live in a state where Subarus are considered the state car). So the responses here are making me a bit uneasy.

"Could be a broken ringland, burnt valve, or 'just' a tight valve clearance."

Are there major differences in the fixes for these problems i.e. if they pull the engine and get in there and find that it isn't a burnt valve but is actually the ringland and now my bill is a grand more or worse and the car is just screwed beyond reason?

A compression test cannot reveal which valve is leaking. A leakdown test can do that.

 

 

Could be a broken ringland, burnt valve, or 'just' a tight valve clearance.

Ok, so cylinder 2 being at 60 psi doesn't mean that's the leaky one?

Car has 117k miles on it fwiw.

Just had the car in the shop. Over the last few weeks there were some misfires w/ a blinking check engine that would go away. Check engine would blink at idle then stop at speed.

Here's what the shop said:

Initially said that check engine code was for cylinder #3. Tested the spark plug and coil pack. Still had rough idle. Did a compression test and found that cylinder 2 was at 60 psi.

Quoted $2k to pull the engine and fix the valve.

So, now in reading tons of threads here and elsewhere I'm wondering why they didn't perform a leakdown test. Is it a bad sign that they didn't? Are they jumping the gun on a diagnosis to line up a big job? Or maybe since the compression test showed only one valve out of wack (my assumption since they only gave me the value of cyl 2) then a leakdown test wasn't necessary? One thread I read is that carbon build up on the valve may cause these types of misfires/low compression? So, is there an easy way to fix/test that like Sea Foam?

These guys work on a metric shit ton of Subarus so I don't have any real reason to think they're talking out of their asses, but I am a bit wary here since the said the CEL code was for cyl 3 and then the compression check showed an issue in cyl 2 (frankly could have just been that the guy misspoke) and also the fact that they would't do a leakdown test which seems pretty standard.

The engine was still idling rough when I parked it at home.

Thanks.

Map gas or preferably acetylene. A heat induction gun may work but I find they dont heat up bolts/nuts enough.

Thanks for the suggestion. When I was down there I actually noticed a fine crack at the back of the flange so I think I'll probably just take it to a muffler shop and get a new flange welded in.

FWIW, I bolt my exhaust on with standard bolts, washers and nuts. I don't use those springs.

 

Hint, use anti-seize compound on all the nut & bolt threads you put on the car, yes even the lug nuts.

 

You do know that a 3" catted downpipe and a tune will really wake the car up and be better then stock. You can even get better mpg.

Trying to fix this right now and I can't for the life of me get the second cat off. The bolts at the bottom of the first cat are quite rusty. Any tips here?

2006 Spec B.

So the gasket between the downpipe/cat and before the second cat has rusted out and there's a gap leaking exhaust. Where I'm having an issue is separating the two pipes so I can put a new gasket in.

Here's the confusing part- I took off the first nut and whats left is the threaded bolt which goes through both flanges but there's no apparent way to screw that threaded section out since there's nothing to latch onto but the threaded section. Does that make any sense?

I've searched high and low but most of the results are for replacing the gasket behind the second cat.

Edit:

I think I figured it out. You need to pull off the whole midpipe/cat by sliding the piece off the bolts and then replace the gasket. So if I'm pulling that off should I replaced the rear hardware i.e. the spring bolts and the donut gasket or are those fine to reuse? Thanks.