Gas milage

[Uncle Ben]

My 1999 OB 2.2 has lost efficiency. On the highway at the speed limit
it used to get 30 mpg. Now it is only 24. That's serious!

Back in 1950, I would change the plugs, the condenser, and the points,
and adjust the timing with my trusty strobe. Nowadays I have no clue.

What should I look for to fix this problem, short of trading it in?

U.B.

 

[Carl 1 Lucky Texan]

My 1999 OB 2.2 has lost efficiency. On the highway at the speed limit
it used to get 30 mpg. Now it is only 24. That's serious!

Back in 1950, I would change the plugs, the condenser, and the points,
and adjust the timing with my trusty strobe. Nowadays I have no clue.

What should I look for to fix this problem, short of trading it in?

U.B.

I assume you've taken into account things like weather conditions,
possibly low tire pressure or slightly different tire size and logged
the difference over more than one tankful.

One possibilty is the engine temp sensor (not temp gauge sender)
The ETS can fail in such a way that it prevents the ECU from leaning the
mixture out. It basically thinks the engine is cold and the 'choke'
should be set all the time. It can fail and NOT set a check engine light
I think.

Carl

 

[Sam]

I'd check the air filter first. If that doesn't work, and they
haven't changed in awhile, plugs and wires can do a lot for fuel
economy. There's no points, condenser, or setting timing anymore -
that's all handled electronically. You can, however, still check the
timing with a timing light to make sure the electronics are working
properly.

 

[hippo]

My 1999 OB 2.2 has lost efficiency. On the highway at the speed limit
it used to get 30 mpg. Now it is only 24. That's serious!

Back in 1950, I would change the plugs, the condenser, and the points,
and adjust the timing with my trusty strobe. Nowadays I have no clue.

What should I look for to fix this problem, short of trading it in?

U.B.

You don't say over what sort of mileage the change has occured. Everything
in previous responses sounds good. IME gradual deterioration is more likely
caused by a consumable item needing changing, sudden deterioration by a
component failure or loss of adjustment. Cheers

 

[AS]

mmm, thermostat?

 

[Mike]

I have my vote for all of the above---

Thermostat, air filter, tire inflation/condition....
any chances you're running the car longer to warm up in the mornings?
also take into consideration changes in local fuel supply...
my 98 hates ethanol and runs poorly on it to prove it.

lastly...any check engine light/codes pulled?
Even intermittent (and self clearing) could indicate a problem to be
checked more closely.

 

[S]

Hi Ben!

What should I look for to fix this problem, short of trading it in?

It never hurts to install a fresh air filter, but in my experience
it's not going to make much difference unless the one currently
installed is really dirty. I'd try the plug wires first, and get a
good set that fits well, particularly the cap at the coil end. This is
a common issue on the 2.2l motors, especially as they get older. You
will be amazed at how much better your car will run if you replace
plug wires that _are_ starting to go out . . .

Beyond that, check the engine coolant temperature sender as someone
has already suggested (check by replacing it; only about a $10 part
IIRC). There may be two temperature sensors on your car (the second
one works the instrument panel gauge), if so, be sure to replace the
right one. Also run an OBD II diagnostic and engine compression test.

FWIW, oxygenated fuels can (will) cause mileage to drop as well;
usually around 10%. I'll assume you have already taken this into
account.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[Uncle Ben]

This is just to acknowledge the 6 generous people who are trying to
help me regain the good milage I used to get in my 1999 Leg. OB. At
last I am getting around to trying out their suggestions.

1. I don't know whether the problem arrived suddenly or over a period
of time, since I don't check milage often enough.

2. I have now replaced the air filter and will find out soon what
effect that change causes. I have a regular appointment on Wednesday
evenings that takes me 240 miles. (The old one looks pretty black to
my untutored eye.)

3. I have new plugs and have ordered new ignition wires, The plugs
are so deep into the engine compartment that I will get my mechanic to
make the replacement.

4. The other suggestions will also require the mechanic's help, so
I'll report later if any temperature sensor replacement has any
effect. I doubt it because a too-rich mixture should cause some smoke
out the back if it is severe.

5. Tires are new and the change in diameter is in millimeters of
tread. I am looking for a 20% effect, so I doubt that one.

Thanks again to you guys.

U.B.

 

[Uncle Ben]

Air filter. --

Wow! With a new air filter, I made my Wednesday night trip of 240
miles. The gas milage increased from 24 mpg to 32 mpg. Quite a
return on my $8 investment. I have learned to change the air filter
every 150,000 miles whether it needs changing or not!

Plugs --

I won't have a good test before next Wednesday, but I learned
something interesting. For 8 years I thought I had a 2.2L engine, it
turns out that I have a 2.5L engine. As such, it is recommended to
use platinum plugs. Four platinum plugs run $100+ ! And the wires
cost another $100.

I chose the non-platinum plugs, but I had to take the high-priced
wires. Next Wednesday I will again measure the milage. But my goal
of 30 mpg has already been met with just a change of air filter. It
is hard to believe that the new plugs will take the mpg from 32 to 40!

I won't report again unless there is an unexpected result.

U.B.

 

[Brian]

Air filter. --

Wow! With a new air filter, I made my Wednesday night trip of 240
miles. The gas milage increased from 24 mpg to 32 mpg. Quite a
return on my $8 investment. I have learned to change the air filter
every 150,000 miles whether it needs changing or not!

Plugs --

I won't have a good test before next Wednesday, but I learned
something interesting. For 8 years I thought I had a 2.2L engine, it
turns out that I have a 2.5L engine. As such, it is recommended to
use platinum plugs. Four platinum plugs run $100+ ! And the wires
cost another $100.

I chose the non-platinum plugs, but I had to take the high-priced
wires. Next Wednesday I will again measure the milage. But my goal
of 30 mpg has already been met with just a change of air filter. It
is hard to believe that the new plugs will take the mpg from 32 to 40!

I won't report again unless there is an unexpected result.

U.B.

150,000 on an air filter? A little sooner would be good too.

Since you're already in the market place buying things, care to make an
offer on a bridge? Only joking.

The prices for plugs and wires, umm, does that include installation, or is
that going to cost you extra? I don't suppose your mechanic mentioned how
platinum plugs are going to raise your fuel economy so well? If it were
this easy, FHI would use those plugs in all their vehicles to get around
classifying some as trucks to meet mileage requirements. You might find out
the brand of plugs you are being sold and post here, as some really do not
work well in Subies.

Your costs sound a little padded to me.

If you are putting performance wires in instead of standard I could see
$100, but you have to understand that low resistance wires tend to hit a
coil harder and tend to require a coil that can recoup faster than the
standard. I would figure it to be similar with a coil pack setup as your
Subie would have.

For the $200 in plugs and wires you are looking to spend, you could pay for
3 or 4 standard plug/wire sets.

On the other hand, when the air filter in my brother's BMW was as black as
night, he had similar problems. Course, after he tuned-up the motor the
transmission went.

~Brian

 

[Uncle Ben]

The prices for plugs and wires, umm, does that include installation, or is
that going to cost you extra?  I don't suppose your mechanic mentioned how
platinum plugs are going to raise your fuel economy so well?  If it were
this easy, FHI would use those plugs in all their vehicles to get around
classifying some as trucks to meet mileage requirements.  You might findout
the brand of plugs you are being sold and post here, as some really do not
work well in Subies.

 

[Uncle Ben]

 You might find out
the brand of plugs you are being sold and post here, as some really do not
work well in Subies.

Your costs sound a little padded to me.

The platinum plugs are recommended by Subaru for the 2.5L engine, so
I'm safe there. Installation is extra, and well worth the price,
because to install the plugs you have to disconnect the engine mounts
and raise the engine -- or something like that. Standard labor charge
is for 1.5 hrs.

 

[John O]

because to install the plugs you have to disconnect the engine mounts

and raise the engine -- or something like that. Standard labor charge
is for 1.5 hrs.

No, it's not *that* hard. I did all four in about 30 minutes, and I've
never done them on this car before. And I'm no mechanic, either.

-John O

 

[Uncle Ben]

 No, it's not *that* hard. I did all four in about 30 minutes, and I've
never done them on this car before. And I'm no mechanic, either.

-John O

Thanks, John. The mechanic I dealt with is highly touted in these
parts for honesty and knowledge, but this was the first time I used
him. Maybe I'm getting educated!

 

[John O]

because to install the plugs you have to disconnect the engine mounts

No, it's not *that* hard. I did all four in about 30 minutes, and I've
never done them on this car before. And I'm no mechanic, either.

-John O

Thanks, John. The mechanic I dealt with is highly touted in these
parts for honesty and knowledge, but this was the first time I used
him. Maybe I'm getting educated!

Replacing them does require the removal of the air filter assembly on the
passenger side and the washer fluid resevoir on the driver's side. Maybe
it's easier for them to mess with engine mounts instead? Either way, it's a
PITA to replace the plugs, so install good ones that will last.

-John O

 

[Uncle Ben]

Replacing them does require the removal of the air filter assembly on the
passenger side and the washer fluid resevoir on the driver's side. Maybe
it's easier for them to mess with engine mounts instead? Either way, it's a
PITA to replace the plugs, so install good ones that will last.

-John O

John, after studying under the hood a while, I think you've got it.
My mechanic has already put in the low-priced plugs. In 30,000 miles
they should be ready to be replaced and I am going to try your method.

Thanks very much.

U.B.

 

[John O]

John, after studying under the hood a while, I think you've got it.
My mechanic has already put in the low-priced plugs. In 30,000 miles
they should be ready to be replaced and I am going to try your method.

Thanks very much.

You're welcome, but I can't take the credit...someone else here mentioned it
and posted some good instrux long before me. I bought a 3/8 knuckle
adapter and a short extension that allows some flex, anticipating this was
going to be trouble. Turns out that the plug socket and ratchet were all I
needed. It was tight, but it worked. I bought the Stanley set of sockets at
Walmart.

-John O