Lousy gas mileage not due to fuel leaks

[bfg9k]

My latest attempt at diagnosing my '98 Legacy L's lousy highway mileage (20 mpg) involved searching for fuel leaks. I added a fluorescent dye (from http://www.autobarn.net, $6) to the gas tank and following directions let the car idle for 10 min. Using a blacklight I searched all around the engine bay and under the car. There are no gas leaks that I can see.

 

So, there is still the VERY strong gas stench around the front of the car (even thru the interior vents) when starting in the morning, esp. after the car has sat over the weekend. This smell is what motivated the use of the dye.

 

I have not yet replaced the rear O2 sensor (I have done the engine coolant temp sensor, thermostat, front O2, plugs & wires). I suppose I could also have a leaky fuel injector.

[Legacy777]

It's possible there is a leak/cracked hose in the evaporative emissions system, which would let fuel vapors leak out. I don't think the dye would work for this.

[bfg9k]

It's possible there is a leak/cracked hose in the evaporative emissions system, which would let fuel vapors leak out. I don't think the dye would work for this.

 

Good point. I'll pull out my Haynes manual and poke around during my lunch hour tomorrow...

[friendly_jacek]

My latest attempt at diagnosing my '98 Legacy L's lousy highway mileage (20 mpg) involved searching for fuel leaks. I added a fluorescent dye (from www.autobarn.net, $6) to the gas tank and following directions let the car idle for 10 min. Using a blacklight I searched all around the engine bay and under the car. There are no gas leaks that I can see.

 

So, there is still the VERY strong gas stench around the front of the car (even thru the interior vents) when starting in the morning, esp. after the car has sat over the weekend. This smell is what motivated the use of the dye.

 

I have not yet replaced the rear O2 sensor (I have done the engine coolant temp sensor, thermostat, front O2, plugs & wires). I suppose I could also have a leaky fuel injector.

 

Leaky injector should be easy to diagnose by:

1. significant fuel in oil, 4-5% or more.

2. fuel pressure disappearing after shutting down.

3. car hard to start when hot engine (flooded).

 

Have you looked into the the gas evaporation system?

Can you pinpoint where the smell is coming from by the lighter test (just kidding!).

 

I vagely remember that some recent batches of subarus had engine compartment gas leaks from rubber lines loosing seal when very cold. There was a TBS but not a recall. Is your problem temp dependent?

[Suzam]

I belive the leaking gas lines was on the Phase II 2.5's

[bfg9k]

Leaky injector should be easy to diagnose by:

1. significant fuel in oil, 4-5% or more.

2. fuel pressure disappearing after shutting down.

3. car hard to start when hot engine (flooded).

 

Have you looked into the the gas evaporation system?

Can you pinpoint where the smell is coming from by the lighter test (just kidding!).

 

I vagely remember that some recent batches of subarus had engine compartment gas leaks from rubber lines loosing seal when very cold. There was a TBS but not a recall. Is your problem temp dependent?

 

Ah, then I'd say I don't have a leaky injector. The poor mileage is year-round, but the gas smell is worse in cold weather. Unfortunately I don't have a garage to use, so wind makes finding fume leaks tough