10 MPG Outback

[nicolo69]

Let me introduce me My name is Jorge and i live in Merida, Mexico a city close to Cancun the climate it is hot, we dont have winter just hot or really hot. In Mexico there ir not a subaru distributors.

 

Last year I bought a Subaru 1996 2.5 DOHC Legacy Outback found in a mechanic backyard, the trans was blown, after many monts researching i was able to fix the transmision. The engine was running fine from the begining, after a few monts of driving the car I notice the head gasket was blown, order the head gasket at the Autozone and fixed. I also change the waterpump,PCV valve, front oxigen sensor and add a transmission cooler.

I love this car, it has 131,000 miles and is in good condition.

But the main problem is that I only get 10 MPG in city driving and last time I check a full tank it last me only 250 miles.

So far i try almost anything, I have a LM-1 wide band a few week a go I put it on the tailpipe and found the A/F ratio it`s on the rich side, almost all time it`s on the 14.5 range, considering the sensor it`s on the tail pipe after the cats thats really rich but the car don`t show any trouble code, drive nice, idle ok, shift decent.

I allready check the voltage on the maf, tps, map and its ok.

On highway if I floor the pedal it goes about 10.0 A/F and you can smell the the tail pipe hard.

Also to consider, becouse the car was sitting almost 2 year the tires were bad, the only tires I have was a 225/75/R15 a little big for the car but fitted nice.

Any ideas why the car is gulping gas?

My next guess is replacing the spark plug wires it looks old but allready check the resistance and its on specs

Thanks in advance

Edited June 5, 2010 by nicolo69

[idosubaru]

you said 250 miles - that's more than 10mpg. your mileage is also off if your tire size is bigger than stock. your odometer will read lower than you're actually traveling, but probably not much? google miata tire size calculator to check differences.

 

dragging brakes can impede mileage. the calipers slides need to be cleaned and greased. a lot of folks don't do it and that car sat for a few years.

 

i would check the spark plugs? air filter?

 

sounds like you covered some things, folks will pipe in with all sorts of possibilites, runs about as many as you have time to sit and conjecture.

[nicolo69]

The car was sitting for 2 years without starting the car, but wen I took the car to my garage the only problem besides the trans, was a bad fuel pump, put a new one, fresh battery and star at the second try.

Anyway put new spark plugs, filters and oil.

I forgot to mention, today I made a back pressure test and was ok, no back pressure PSI.

And the 250 miles on my tank was highway miles. I took a small trip on April and top fill the tank.

Edited June 5, 2010 by nicolo69

[idosubaru]

that is awful gas mileage.

 

dragging brakes?

 

leaking injectors?

 

there's probably numerous possibilities but those are two that *might* be affected by sitting for a long time?

[Fairtax4me]

Tire size is quite a bit larger, but the biggest thing is your math is way off.

10mpg would only get you 160 miles on a FULL tank (15.9 U.S. gallons) . At 250 miles you are getting at least 15.5 mpg. But it's probably more like 18-19 mpg if you fill up when the gauge first reads empty. Most of these cars if the gauge says empty it will take 11.5 - 12.5 gallons to fill. 250 miles on 12.5 gallons is 20 mpg.

Now add to that your larger tires, which will make the speedometer read slow. This also causes the Odometer to count slower, so you may in fact be getting closer to 270 miles per tank allowing an approximate 7.6% bump due to the tire size. Your current tire size is larger than the stock size by roughly 7.6% according to the tire calculator here. http://www.miata.net/garage/tirecalc.html

 

All of a sudden you're getting 21+mpg which is pretty normal for mixed city / highway driving.

[Olnick]

Welcome nicolo69. Congratulations on your perseverance in fixing the transmission and getting your Subie running.

 

Your mileage isn't as bad as you think--250 miles divided by 15 gallons is actually 16-17mpg. And it may be even better because of your tire size deviance!

 

For sure replace the plugs (use NGK) and the wires (Subaru OEM if you can get them), new air and fuel filters, new PCV valve. Might want to clean the MAF sensor and the IACV. And check the brake sliders as grossgary said. New O2 sensor maybe? (Do you get any CEL lights?)

 

Good luck, keep up the good work and ask lotsa' questions.

[nicolo69]

So far I try almost anything, vacum test, back pressure test, diferent fuel, diferent spark plugs, new front O2 sensor, check brakes, diferent oil, check EGR, all check ok.

I have a generic scantool, the only problem found was a bad switch selector, fixed and never return.

Becouse of the climate it is common here to cancel the heather core and some mechanics took out the thermostat on the cars, check mine and did not have, so i put a new one. The hoses coming and goin to the heather core are canceled not looped.

keep in mind at 7:00 am the outside temp are 25 degrees celcius and by 3:00 pm are 40 degrees celcius almos every day betwen march and november.

WE DONT USE THE HEATHER ON THE CAR NEVER

[Olnick]

Becouse of the climate it is common here to cancel the heather core and some mechanics took out the thermostat on the cars, check mine and did not have, so i put a new one. The hoses coming and goin to the heather core are canceled not looped.

 

Interesting. Raises some questions in my mind:

 

Isn't the routing through the heater core part of the coolant circulation system? Is capping the heater hoses a bad thing to do? Could it cause improper readings from the ECTS and thus affect proper operation of the engine? Would it be better to loop the hose?

 

Just some thoughts for discussion!

[idosubaru]

i guess if the car isn't getting up to operating temperature it could be running in "closed loop" indefinitely. but sounds common to do where he is and it's really hot.

 

if you got a temp gun, hit the hoses sometimes while driving. try different conditions, like extended highway, in town, etc. seems like it should be getting plenty hot, but who knows?

[nicolo69]

Hello again:

At this time I am not able to find the solution for my car i try a new few things but the car still the same.

One intresting thing that i found today is, according to the service manual the rear O2 goes after the second cat and my car has it behind de first averything looks in place no mods to the catback or downpipe, anyway i dont think this a factor to my fuel consumption.

But one thing I notice is, if I disconect the rear O2 there is no cel ligth and the scanner dont show any activity on the reading beside .300 mv so at this point Im start to think there is some trouble on my ECU. I aready check wiring, diferents rear O2 sensor and the result it is the same, no cel ligth even after many trips and the A/F ratio remain at 14.5 (rich)

I really need some expert advice

Thanks

[Suzam]

That should throw out a CEL. Does the CEL light up when you first turn the key to start? If not maybe your CEL bulb is out.

[nicolo69]

Yes it does, actually last week I have a check ligth becouse it rains and the spark plug wire get wet, was a misfire code.

[nipper]

The rear o2 sensor tells if the cat is working. The front o2 is for the ecu.

 

First find a measured mile on the highway (signs on the side of the road are measured miles. Match that to your trip odometer.

 

- A bad o2 sensor will give poor gas milage.

- A sticking or bad Idle Control Valve (which may not throw a code) will cause bad gas mileage.

- The higher thrust it takes to launch the car (yes it is measured to become thrust) will reduce gas mileage.

- Improper tire pressure

- The beginings of torque bind

- Seized brake caliper

- Stuck parking brake

- Driving over 70mph, as that seems to be the tipping point from 28-29 to 25-26 or lower the faster you go.

- Heavy right foot. Slow acceleration and not running out gears will help.

- Timing belt acting wierd. After sitting for 2 years i would replace it and all associated parts.

- A non OE thermostat.

 

If you are starting out at 23-25 then add these it will make it lower. Add any of these together your mileage wil get dramatically lower.

[Ionlyhave3suubs]

I have read to check out the brakes a couple of times. The calipers on these cars are designed to slide back and forth on their mounts. A caliper stuck due to corrosion, rust, or other debris can cause the calipers not to slide as they are designed to. Next time you drive your Outback for a significant distance, especially with a lot of stop and go, when you park get out and check your wheel temperatures. Go to each wheel and feel the metal part of the wheel close to the lug nuts (your car should have alloy wheels if they haven't been changed). Compare the temperatures by feel. If one feels hotter than the rest, I would suspect a caliper problem on that wheel. The caliper could be either sticking (not fully releasing) or not properly sliding back and forth. If you have a hot wheel, start with that wheel. Pull the wheel off. Remove the caliper, clean the caliper flat surfaces where they slide against the stainless steel guides and clean those stainless pieces. Clean them by wiping off an grease, debris, then use a spray cleaner designed for brake parts. If rusty, using a fine sandpaper also may be necessary. After you get it good and clean, apply a thin coat of High temp caliper grease to the stainless pieces where they contact the caliper sliding area. Then reassemble. Your increased tire size could also be a problem. A 225/75-15 tire is large enough that it could be causing interference problems, especially with the rear struts. I have a 97 outback (same bodystyle, and nearly identical in design). The tightest tire clearance with the tires in the rear struts, between the back side of the tire and the part of the strut that faces outward. You could have rear tires rubbing against the rear strut (especially if you have an alignment problem). to check for this, remove your rear wheels if the tires rub, you will have areas just behind the top of the tires on the strut where the road dirt has been rubbed off. If this is not seen, you probably don't have a tire rub.

 

Also tire inflation has been mentioned, but you have not mentioned checking this. I run 30 psi in mine all the way around. Uneven tire pressure can cause serious drivetrain wear and failure on these AWD vehicles. Improper inflation will also have negative effect on fuel mileage.

 

The outback drivetrain was designed to turn 205/70-15 tires. Turning the larger tires causes the engine to work harder to accomplish the same distance traveled, not to mention you are traveling a longer distance than your odometer is measuring, thus throwing off the accuracy of your miles per gallon calculations

 

With regard to your air/fuel mixture readings, I would look at your coolant system first. Verify your thermostat opens and closes at the correct temp. You can test the thermostat by removing it and placing it in a pot of hot water on the stove. Use a food cooking thermometer and heat the water with the thermostat in it until it opens and check that it is opening at the temp recommended by the factory specs. if the thermostat is opening too soon or sticking open, the engine can operate below proper temp (even in hot climates) causing the engine to run in closed loop mode. In closed loop, the engine will run rich (more gas than needed) which will increase fuel consumption. If it were my car, I would also bypass the heater core rather than cap it, so coolant can flow through.

 

Ignition- Go ahead and buy SUBARU brand spark plug wires, order them online if you have to. replace them and replace the spark plugs with the proper NGK plugs.

 

I love my Outback too, but fuel mileage is not what I consider its strongest point. I have gotten as high as 29MPG in highway driving by using a very light right foot. My 230k mile Subaru usually averages around 20 MPG in mixed city/highway driving. When mine was younger it got around 24mpg in mixed driving. AWD is great, but it uses a little more gas.

[SuBrat84]

I don't think the problem here is the car, my friend. I think it is your math. If you are going 250 miles on a tank of gas and only get 10 MPG then you have a 25 gallon tank. Can you put 25 gallons in your car at one time?

The MOST MOST MOST gas I have EVER fit into my 1997 Outback 2.5 DOHC was 14 gallons. (and believe me I BARELY made it to the station.) I get 250-280 miles from that. 20 MPG x 14 Gallons = 280 miles. I Do a bit better if I ONLY drive on the freeway.. 22-23mpg. Maybe like 18mpg around town because I drive kind of hard.

How to figure out gas mileage:

Fill up your tank.

Reset your "trip meter." (or write down your miles.)

Drive for X miles. (X = 100.)

Fill up your tank with Y gallons. (Y = 5)

 

X miles / Y gallons = Z mpg.

100 / 5 = 20 mpg.

Edited December 2, 2010 by SuBrat84

[nipper]

I don't think the problem here is the car, my friend. I think it is your math. If you are going 250 miles on a tank of gas and only get 10 MPG then you have a 25 gallon tank. Can you put 25 gallons in your car at one time?

The MOST MOST MOST gas I have EVER fit into my 1997 Outback 2.5 DOHC was 14 gallons. (and believe me I BARELY made it to the station.) I get 250-280 miles from that. 20 MPG x 14 Gallons = 280 miles. I Do a bit better if I ONLY drive on the freeway.. 22-23mpg. Maybe like 18mpg around town because I drive kind of hard.

How to figure out gas mileage:

Fill up your tank.

Reset your "trip meter." (or write down your miles.)

Drive for X miles. (X = 100.)

Fill up your tank with Y gallons. (Y = 5)

 

X miles / Y gallons = Z mpg.

100 / 5 = 20 mpg.

 

 

And best to do that with 3 fill-ups.

[Fairtax4me]

I don't think the problem here is the car, my friend. I think it is your math. If you are going 250 miles on a tank of gas and only get 10 MPG then you have a 25 gallon tank. Can you put 25 gallons in your car at one time?

The MOST MOST MOST gas I have EVER fit into my 1997 Outback 2.5 DOHC was 14 gallons. (and believe me I BARELY made it to the station.) I get 250-280 miles from that. 20 MPG x 14 Gallons = 280 miles. I Do a bit better if I ONLY drive on the freeway.. 22-23mpg. Maybe like 18mpg around town because I drive kind of hard.

How to figure out gas mileage:

Fill up your tank.

Reset your "trip meter." (or write down your miles.)

Drive for X miles. (X = 100.)

Fill up your tank with Y gallons. (Y = 5)

 

X miles / Y gallons = Z mpg.

100 / 5 = 20 mpg.

 

That's exactly what I tried to explain in reply #5.

 

Isn't the routing through the heater core part of the coolant circulation system? Is capping the heater hoses a bad thing to do? Could it cause improper readings from the ECTS and thus affect proper operation of the engine? Would it be better to loop the hose?

 

That's an interesting thought. I'm not sure it would have much effect in a warm climate.

Although the heater circuit of the cooling system doesn't transfer much heat away from the engine, it does serve a purpose of acting as a bypass to maintain proper cooling system temperature. The heater hoses route coolant from the crossover pipe under the intake, through the heater core, then back through the bypass pipe to the back side of the thermostat housing on the water pump. It keeps hot water moving through the system to the thermostat, so it's less likely to close in cooler weather due to cold coolant (a lower temp than is required to keep the thermostat open) flowing in from the radiator. Thus it prevents the engine from essentially overheating in cold weather or in scenarios where a constant flow of air across the radiator sufficiently lowers the temperature of the coolant moving through it.

 

One intresting thing that i found today is, according to the service manual the rear O2 goes after the second cat and my car has it behind de first averything looks in place no mods to the catback or downpipe, anyway i dont think this a factor to my fuel consumption.

On the US models at least, the first O2 sensor is on top of the first cat in a pretty well hidden spot. You can see it from above if you look under the passenger side half axle, it is directly underneath the inner cv joint.

 

As said before the rear O2 sensor has no effect on fuel economy, it is only for checking efficiency of the catalytic converter. As for the voltage even with the sensor unplugged. It seems to be common for after market scanners to show a stepped up voltage reading for one or both O2 sensors. Something about the way the ECM output is translated by the scanner.

[nicolo69]

First i want to thank everyone for the advice.

 

I want to make things a little more clear, I am a mechanic I have a small mechanic shop here in Mexico, thats one of the reason I buy this car because every part here is hard to find and I know the car is gona need some care after so many time whit no use.

All the basic troubles has been check (tires, brakes, wiring, plugs, fuel pump, HG, O2 sensor, etc), I am able to drive the car whit the scanner plugged and check the behavior of the engine.

The heater core it is already looped put a fresh new thermostat a few months ago, still the same, I am aware the tires are bigger but does not explain the A/F problem.

I am confident if I change the tires my fuel consumption is gonna improve but again It does not explain the A/F ratio.

The only important part I did not change yet because as mention before is hard to get are the spark plug wires, I am on the process of order a new ones among the brake pads, hopes this fix the issue on the A/F.

Thanks again.

[Ricearu]

if you are running at stoichiometeric a/f ration (14.7:1) then your mileage will not get any better, and if you FLOOR IT, it WILL Richen up to 10:1... My forrester gets 300miles to a tank which is roughly 24mpg or so.

[nicolo69]

I know A/F it is not the same on all the powerband, but I really can tell you I does not feel right the car has some kind of problem. Actually wen I step on the gas the A/F goes way out of band (below 9.0) you can smell the tail pipe from inside the car, believeme it is not normal.

I did not have the opportunity yet but I was thinking on borrow a APEXI SAFC and do some tweaks on the car to figure out thinks.

Last weak I have a car that show similar problem and turnout to be the timing belt so took mine and check the timing belt it was ok.

One thing is for sure the day I fix my car you gonna know why.

 

Thanks

[Ross]

It would be interesting to see what your LM-1 would tell you if you put the sensor in place of the engine O2 sensor and took it for a drive -- I presume the LM-1 has a programable analog output you can plug in to the ECU to keep it happy?

 

If you could get a log file for a drive showing the actual A/F ratios it may provide some clues.

 

For instance, is the mixture only far too rich during cruising, closed loop operation, or is it too rich all the time, even when the decel fuel cut should occur.

 

One thing -- you mention that you checked the voltage on the MAP sensor -- the EJ25D that I am familiar with does not have one.... Is the engine the car's original one?

 

Read nicolo69's posts properly before you start berating him on his maths skills..... He clearly states that the 10mpg is city driving and the 250mile tank was highway.

[SuBrat84]

I wasn't trying to berate his math skills. It just seems like 18-19mpg on the highway vs. 10mpg around town is a HUGE difference. If this is truly the case then here are my suggestions:

Have you tested the fuel pressure?

Have you tested the fuel injectors?

Have you replaced the knock sensor?

Air Filter? Fuel Filter? (You said "Filters" but didn't specify.)

Are you using the NGK PFR5B-11 Spark Plug?

You need to get GENUINE SUBARU plug wires!

Have you tested the coil and igniter to make sure they are in spec?

Have you cleaned the MAF with a good MAF cleaner?

Have you check for blockage in the air intake system?

 

I wish you the best of luck and I do apologize if I seemed offensive. I was not trying to insult you.

[nipper]

Ok you may have a small shop, but there is one tool that everyone seems to forget about.

 

The vacume gauge. It can give you so much information.

 

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

 

Lets give that a check.

[nicolo69]

Non taken.

The LM-1 does have a analog output but only to read voltage it does not simulate the O2. I am planning to install an extra bung next to the O2 sensor to check real A/F

All the filter were change oil, air, gas.

Fuel pressure checked, EGR, coil, wires, back-pressure, manifold vac, new plugs, different plugs, different MAF you named I can try it.

About the deceleration cut it only occurs if the car goes above 40 miles and after stepping on the break or downsifth manually.

Another observation, the shifts are controlled by a TECU and this work around the MAF, TPS and VSS among other sensor, Ok. If I am crisng on the cruise control and the car goes over a small bridge uphill the trans down************f more than needed and on rare ocations it does not return to te 4 overdrive, I need to dissengage the cruise control change vehicle speed and the trans return to normal, but I fell this more like a bug (or maybe the tire size) on the TECU than a problem.

I am gonna keep trying on this car because I loved, like I mention before there is no SUBARU in Mexico until recently and I felt in love whit the Outback Wagon since I saw a TV commercial whit crocodile Dunde many years ago, so wen I saw this car around town I never hesitate to buy it.

I already toked to the beach on camping a was a dream come true but with mosquitoes.

Tanks

[nipper]

Thats typical Japanese 4 cyl cruise conrol calibration. If you are in a loit of rolling hills use Drive 3, it will really make the car much happier.You just shut it off and drive uphill, it is not a bug as much as a silly design feature.

 

Do the vac gauge like I suggested and post the results here. There is no such thing as too much data for those of us who do not have the car infront of us. If your code reader wil do it can you give us the % of load at idle, 30mph and 60 mph on level ground (or the avg load).

 

Hrmm the decelration only happening above 40, i think we may have a clue. It should happen all the way down to where the car will max out if allowed to creep at idle. Some cars will get up to 15mph due to tranny calibration.

 

How is your wheel alignment?

 

Have you tried better fuel?

 

Forgive me if I am repeating myself as this thread has gotten long, but was the knock sensor replaced. Is the egr functioning.

 

Do you have a scangauge so that you can read these things on the go and get a real MPG reading?

 

 

 

Is your cat clogged? I sort of wish we had data and not information on what you checked as that would give us more information.