Jump to content
Ultimate Subaru Message Board
kmpdx

Guys, like 95% sure it is restricted exhaust.

Recommended Posts

So I finally had a day that I could troubleshoot. I got the vacuum meter hooked up and following some different videos I show that vacuum when warm is below 20 and that around 2000 RPMs it drops. Furthermore, when I started it on a cold day, so little vapor seemed to come out of the tailpipe. Also, the front catalytic convereter always smoked a little from oil but now that thing smokes like crazy making me think that it is even hotter than it was before. I know that's not the best indicator but does seem to fit too. 

 

So I am trying to figure out what to do. If I wait a few weeks, I can try to drop the exhaust and confirm it, then what? My sense tells me that it is the front catylitic converter. How would I confirm this? Get it apart and look through it?

 

There is supposed to be a good muffler shop here in Ashland. Should I just take it to them and see if they can cut it out and weld in a replacement? Should I replace with a new front y/pipe catalytic converter purchased online?

 

What do you guys think?

 

Thanks,

kmpdx

Share this post


Link to post
Share on other sites

Yes GD,

Here are the other two posts that have brought me this far.

http://www.ultimatesubaru.org/forum/topic/166147-engine-will-not-rev-past-4000-rpms/

http://www.ultimatesubaru.org/forum/topic/166167-question-about-diagnosing-restricted-exhaust/

 

Yesterday when I drove it again it just wont rev past a certain point. Depending what gear I am in power maxes out at a certain RPM and really the fastest I can get is going is 35 or maybe 40 but it is hard to get there. It really never has the power I would expect from the start either.

FWIW, I was keeping track of mileage and was getting around 21-22 mpg right before this happened. This power issue did happen on the freeway and at first I thought a broke a belt or that the fuel pump had gone bad but if it is resricted exhaust perhaps it finally resricted to the point of loising power? 

 

Like I said too, at cold start, on a cold day, I just didn't see or feel the vapor that I would expect even though that may not be the best diagnostic. I cannot drop the exhaust due to current space/tools available at the moment but may be able to in a few weeks.

 

Thanks,

kmpdx

Share this post


Link to post
Share on other sites

Seems there should be an easy test if this is it. Someone more in the know can tell...?

 

On some subarus you can simply remove the front few exhaust nuts and the header will come off the engine enough to drive as a test but is still supported part way back by a bracket close to the trans. Or hang it with wire/coat hangers for a short test drive. Shouldn’t take long and require no more than 14mm socket for the exhaust nuts. And every time I’ve done that there’s zero change in symptoms.

 

I doubt it’s the exhaust. Ive never seen a Subaru converter “clogged” but I’ve seen people try to diagnose/fix those symptoms by addressing the converter without effect. Clearly it happens but Id also diagnose more than that. Which it looks like maybe you have but I’m not able to check those other threads now.

Edited by idosubaru
  • Like 1

Share this post


Link to post
Share on other sites

Thanks idosubaru,

I am not able to drop the exhaust off currently to determine for sure but the lack of power and the vacuum test I did also point to exhaust as the possible problem. It does seem like not a lot of vapor is coming from the exhaust on a cold start on a cold day either. I know that unbolting the exhaust is the step I really need to take but I cannot at this moment. 

 

Once I can definitively diagnose it as exhaust then I will figure out what to do next. If it is ruled out I am going to start checking other things but this is the one I am focusing on first.  Waiting to see what GD thinks about this, too.

 

Thanks,

kmpdx

Share this post


Link to post
Share on other sites

Diagnosing a restricted exhaust w/a vacuum gauge can be tricky until the exhaust becomes quite plugged.

I see no evidence of a restriction from your gauge readings so far.

It is completely normal for the vacuum to drop when the throttle is opened.

 

You want to see the gauge at your 4000 rpm limit while driving.

Get some hose.

Last one I did showed a positive pressure on the intake.Proof positive.

 

Better test is a pressure gauge on the O2 port,but,they can be hard to remove.

You don`t need a specialty gauge.

I used a garden variety gauge.It survived fine for the short duration required.

 

The muffler shop may be able to attach a gauge by drilling a hole and plugging it when done.

 

Subes are good in that you can drop the exhaust off the heads for a test.

 

The symptoms described in your other thread sound very much like a partly plugged exhaust.

  • Like 1

Share this post


Link to post
Share on other sites

What is the exhaust pressure like at tail pipe? 

 

Put your hand  over tail pipe  briefly  while engine idling ,  to get an idea of exhaust pressure - should  feel  strong even  pulses for each cylinder firing.

 

Have done this  in the past  to diagnose / feel / listen for  valve problems as well  ie burnt out failing exhaust valves.

Edited by subnz
  • Like 2

Share this post


Link to post
Share on other sites

Just loosen the header - all you need is a 14mm socket, 6" extension, and a ratchet. Don't remove it just drop it down 1/8" or so.

 

Plugged exhaust is rare on Subaru factory cats but happens frequently on aftermarket muffler shop cats, and factory GM and Chrysler cats do this all the time. It's definitely a possibility and very easy to rule out.

 

GD

Edited by GeneralDisorder
  • Like 3

Share this post


Link to post
Share on other sites

OK GD. It may be a few weeks before I can do that due to life factors. It is a Subaru cat so I guess the only thing to do is rule it out by dropping it. I apprecitae the direction that it just needs to be a little bit which makes it sound easier than I was thinking.

 

Naru, I think that to get to the o2 sensor might be the same as just dropping the exhaust but perhaps it's not as hard as I think. I will do it in a couple of weeks. At 4000 RPMs the car does not accelerate anymore and will not return to acceleration until it gets below the upper limit RPMs. I thought that it was due to the exhaust but I suppose it could be something different. I thought that at 2000 RPM I should still see an increase in vacuum not a slight dip that stays slightly dipped. I thought at WOT is when vacuum drops to zero. The gauge I have does both vacuum and pressure So when I do try it if it becomes easier to get at the O2 than the exhaust perhaps I will try that route.  

 

subnz, I do not feel the exhaust like I would expect and like I said, when I started it cold on a cold day and it goes to high idle, there just is not the vapor or pressure that I would expect but perhaps I am reading too much into that. Burnt exhaust valves you say? Perhaps that is it. I will explore that path once I rule out the exhaust.

 

My thought is to maybe take it to a muffler shop here in Ashland and just have them drop the exhaust if I cannot get to it to diagnose or rule out the exhaust once and for all or wait a few weeks. If it is not the exhaust I have a few other ideas of what it could be but will save that for a new post.

 

Thanks,

kmpdx

Share this post


Link to post
Share on other sites

You can't just slide under it, loosen the header, and drive around the block? Shouldn't take more than 15 minutes. You can't borrow a 14mm from someone and take 15 minutes to perform this test till several weeks from now? This I don't understand unless you are physically unable to do it from a disability or some such? 

 

You have to have the can-do attitude before you can fix anything. Get out there and make it happen. You know I would....

 

GD

  • Like 1

Share this post


Link to post
Share on other sites

Just keep the gauge hooked to the intake and go for a drive.

Much simpler.

  • Like 1

Share this post


Link to post
Share on other sites

It's because I am on campus housing and we are not really supposed to work on cars in the lot. That being said I have my jack and jack stands out there my truck and maybe I will sneak it in. To do the gauge I need a longer hose. Maybe I will get out there. I am also studying for an exam tomorrow morning but maybe I could use a break. I have the tools. I think you guys talked me into it. I'll be back...

Share this post


Link to post
Share on other sites

Just keep the gauge hooked to the intake and go for a drive.

Much simpler.

 

Yeah but he probably doesn't know what he's looking at on the vacuum gauge. We use O2 sensor adapter and pressure gauge for suspected exhaust restriction. But then we do a lot of turbo cars and that makes the manifold vacuum much harder to interpret because positive pressure can be normal. 

 

GD

  • Like 1

Share this post


Link to post
Share on other sites

It's because I am on campus housing and we are not really supposed to work on cars in the lot. That being said I have my jack and jack stands out there my truck and maybe I will sneak it in....

Oh my this is so easy - at most they’ll say “pack up or finish up next time I come around”. I wouldn’t even think about it. when I was in college I’d do it on campus where I wasn’t supposed to, late at night, drive to a low traffic apartment complex back lot, ask friends for a place off campus, a covered lighted gas station late at night or even closed, and do small jobs. I parked a parts car in a random apartment complex for months while I parted it out. I replaced a clutch cable on campus and the police held a flashlight for me while I did the pedal routing! I’ve left deer in my trunk til 2am, drug them in the kitchen of a dorm when everyone’s asleep, butchered it and chucked the left overs in the dumpster on the other side of campus and cleaned up the kitchen before anyone woke up. all of this was in downtown Atlanta mind you, one block from the largest skyscraper in Atlanta. Not the most convenient place to find space or away from humans.

 

As GD said - there’s a way. resolve and drive were probably as important than a degree. Go practice that resolve and put it in your resume.

  • Like 1

Share this post


Link to post
Share on other sites

Yeah but he probably doesn't know what he's looking at on the vacuum gauge. We use O2 sensor adapter and pressure gauge for suspected exhaust restriction. But then we do a lot of turbo cars and that makes the manifold vacuum much harder to interpret because positive pressure can be normal. 

 

GD

 

For this car it is simple enough.

Any positive pressure in the intake w/the car driven WOT at the limiting speed is bad.

  • Like 1

Share this post


Link to post
Share on other sites

IT IS RESRTICTED EXHAUST!!! Confirmed. I dropped the exhaust down. Fortunately the bolts came unscrewed (well the studs came with the nuts mostly). I took it out for a spin and it had power like never before. Maybe it has been partially restricted since I bought it. You guys weren't kidding about the noise. So now what do I do? How can I know if it is the front or back? Should I replace both or have a shop do a modification? I definitely can get both converters with a Y pipe for like $250 new and shipped. 

 

THANK YOU!

kmpdx

Share this post


Link to post
Share on other sites

Uhhh, I just poked a light into the tailpipe and there is some sort of fiber material like 6 or 8" in. Looking online it seems like that any fiber would insulate a pipe. I am wondering if my muffler is collapsed inside and that is the problem? 

Share this post


Link to post
Share on other sites

Post in the wanted section - I bet someone has a parts car you can pull exhaust from cheap. You will have to buy private party if you want a cat.

 

Or just drop it, hollow it out, and put it back on. Order a new muffler to go with hollowed out y-pipe. They are cheap.

 

Ashland has no emissions and its not like it pollutes more than a WRX with catless exhaust which is like 50% of them in this state.

 

GD

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×