Smoke coming from the exhaust on startup, bad fuel mpg

For the very first time, I noticed dark-colored smoke coming from the exhaust. It only happens on startup, and the first time there appeared to be a lot. It went away after about 4 - 5 seconds. It was sort of a dark blue-ish gray-ish color.

On a second startup, it happened again. It was about an 60 - 80 minutes later, but the smoke was much less. Only lasted a couple of seconds.

I started it up a third time, about 20 minutes later. There was no visible smoke.

Earlier in the morning, I also made a couple "harsh" runs for my G-tech. I did not take advantage of the TC stall speed, but I did mash the gas repeatedly. It could be related, I suppose.



Lately, my gas milage has also been terrible. Every time I get into the car, the tank gauge is about 1/8" - 1/4" inches lower (I can almost see it moving when driving). I checked my fuel milage twice, and it was in the 13 or 14 miles-per-gallon range. I have always gotten around 23 - 25 for freeway driving, and 18 - 19 for city. A mix of the two usually gives about 20. My car does not idle roughly or stall out... ever. I had it stall once, and that was about one year ago. That's it. There does not appear to be a loss of power either, and I think my G-tech times can confirm that.

I just had new tires installed on my car, plus a rear camber correction kit. Therefore, I had all four wheels balanced and aligned. I was hoping that perhaps my alignment/balance was far out of range, and thusly causing the decrease in mpg. I have not had the chance to test the mpg yet, but I will very soon.

And no, I do not have any CEL problems.

Any thoughts?

I forgot to say, I did do a search for anything related to smoke coming from the exhaust. Everything either did not relate, or did not have any answers.

[Earthworm]

You may want to get a sniff of the smoke. It's either oil or gas. Oil could be from failing rings, gas could be from leaky injectors.

There could be other things as well.

Originally Posted by Earthworm

You may want to get a sniff of the smoke. It's either oil or gas. Oil could be from failing rings, gas could be from leaky injectors.

There could be other things as well.

I've been putting a lot of thought into it, trying to come up a "game plan."

For a while now, I have been getting some oil in the intake tract. I replaced the PCV valve about 8k miles ago, so I didn't think it could be the issue. I picked up a new one anyway, and will be installing it soon. I suppose that the oil could be getting into the cylinders, and then burning away. This is my hope, anyway.

As for the smell, I will check it the next time I start it up. When the car is running, it smells like normal exhaust. Makes me feel a little loopy the instant that I sniff the tailpipe, so it must be normal then.

I occasionally get a wiff of burning oil when driving, so now that I think of it, I will definitely check the odor on startup.

As for the fuel milage, and along the same lines as the intake oil problem, I will be cleaning the throttle body and IAC soon. Any recommendations for throttle body cleaner?

I will also be replacing the fuel filter and air filter. Both have been replaced recently, but I may as well give it a shot.

The fuel gauge seems to be holding place much better after my alignment and balancing, but we will see what the numbers show.

If none of this fixes anything, resetting the ECU is next (which is tough for me, as I am always driving somewhere). After that, spark plugs. I will likely do the valve cover gaskets at the same time.

[Earthworm]

Originally Posted by deruvian

As for the fuel milage, and along the same lines as the intake oil problem, I will be cleaning the throttle body and IAC soon. Any recommendations for throttle body cleaner?

I've tried 2 products. The first was carb cleaner and that did a good job of cleaning the throttlebody. The last time I used Mercury Powertune and it did an equally good job but now I don't seen to have the 5mt stall problem anymore. I don't know if it was the Powertune or the new knock sensors that contributed to this.

[DavieGravy]

Interesting note: My father's 2004 Outback VDC does the same thing. Something to do with the horizontal engine perhaps.

Okay, here are my thoughts on this subject. You said that you have no CEL issues, presumably the light comes on initially when you first turn the key on. Dark, bluish grey smoke could suggest either oil in a cylinder or an over-rich condition. Oil in a cylinder could be coming from the valve seals or the rings. Smelling oil on a Sube does not sound so unusual, but from an external source rather than internal. My Legacy smelled that way, but she did not use oil or smoke. The bad gas mileage coupled with the smoke suggests to me an over-rich condition. I am guessing that if something in the FI system fails, be it an O2 sensor or ??? the computer will go into limp home status, which seems likely to be a rich condition. Mileage is linked to fuel rather than oil. It could be an O2 sensor or some other fault in the FI system. Plugs or filters do not seem likely to me. A warm engine is more likely to burn off the excess fuel than a cold one. Anyway, just a thought. John