View Full Version : Horrible gas mileage and bad power following engine replacement

03-03-2012, 07:26 PM
1998 subaru Outback 2.5 liter.
I must be the only person on the planet not aware of the HG problem on these cars. My head gaskets finally failed completely at 100k, and blew out the engine.
I found a very competent engine guy (checked credentials, reputation, references, inspected his shop, etc(), and had the engine, oil pump, and water pump replaced. All belts and timing belts were also replaced.
I noticed immediately that the car had low power. I figured it was just needing to break in. I usually get 24-25 mpg. The first tank, I got 20, then less and less, until I'm now getting 16mpg.
We've had an electronic diagnostics run, checking all the sensors, and they're all fine (including O2, temp, knock, air/fuel ratio). compression is excellent. Catalytic converters aren't plugged at all. No computer codes.
We can't figure out how we can be using 35% more fuel than normal, and have the correct air/fuel ratio? We're considering replacing the computer next. It almost seems like there's additional drag somewhere, causing it to need to burn more fuel. Brakes are good - nothing rubbing.
What on Earth do we try next?

03-03-2012, 08:30 PM
Try clearing the computer codes, even though none are showing.........sometimes this clears things by doing a "reset" of the ecm.
Were the codes checked with a generic code reader or the dealer unit? The dealer one will often reveal codes not visible on generic machines.

Were the correct head gaskets used? Valve timing done correctly? Current compression readings?

03-03-2012, 08:50 PM
How do we reset the computer? Can we do this by simply unplugging the battery?
Codes were checked with a generic reader. The local dealership is know for being, well.... incompetent, so we went to the generic "import place". We can drive a few extra miles and have a better dealership check the codes. Original HG were not used, since they're design-flaw cause the whole adventure int he first place. They were replaced with the correct gaskets that were meant to fix the whole head gasket problem - multi-layer steel, is that right? The guy who rebuilt the engine is the guy that all the area dealerships send their engines to to get rebuilt, so he's pretty experienced. He set the valve-timing, but being human, a mistake could have been made. We can certainly check that. Compression readings are: 173, 169, 161, and 165.
Thanks for the ideas.