Pass smog and improve mileage

[gyuunuuya]

Filled with 91 octane from Exxon

 

Gas mileage has always been horrable on the car not bad, I mean horrable like 12 MPG, with a light foot

92 Subaru legacy AWD non turbo wagon Automatic.

 

 

 

I've done many things to try to fix this problem.

 

1) Replace air filter

 

2) Mass air flow sensor

 

3) O2 Sensor (the one by the exhaust manifold)

 

4) Spark plugs

 

5) Seafoam straight through the injection with a tube and the can.

 

6) tire pressure and new tires

 

7) Oil changes

 

8) My wife has to smog the car since regestration is due, but of course if failed.

 

HC (PPM)

 

Idle

Max = 120

Measured = 230

2500 RPM

max = 140

Measured = 15

______________________________

 

CO

Idle

Max = 1.00

Measured = 1.65

2500 RPM

Max = 1.00

Measured = 0.05

 

I bought another O2 sensor today because I was told that there are 2 o2 sensors on subaru's so I was gonna try to fix that.

 

If your have any other suggestions as to what I can do plz let me know.

 

Also I have noticed that the car temp sensor seems to warm up pretty fast it's fully warm in like 2 minutes of driving lightly. Is it possable a fualty temp sensor can cause all these problems?

 

 

Thanks in advance

[porcupine73]

Hi, sorry to hear that. What model Suby is this and what is the mileage? Sounds like the O2 sensor you replaced is the front; replacing the other (rear) probably won't make much difference in emissions. What brand/octane gasoline are you running?

 

I've heard some tips about trying to pass, but have never tried: make sure vehicle is fully warmed up like 20-30 minutes driving before the test. I leave the vehicle running in the place's parking lot while waiting. Also maybe try running like 4 bottles of isopropyl (not methanol) gas line antifreeze; I've heard this reduces emissions too.

[gyuunuuya]

Hi, sorry to hear that. What model Suby is this and what is the mileage? Sounds like the O2 sensor you replaced is the front; replacing the other (rear) probably won't make much difference in emissions. What brand/octane gasoline are you running?

 

I've heard some tips about trying to pass, but have never tried: make sure vehicle is fully warmed up like 20-30 minutes driving before the test. I leave the vehicle running in the place's parking lot while waiting. Also maybe try running like 4 bottles of isopropyl (not methanol) gas line antifreeze; I've heard this reduces emissions too.

 

Sorry I added that information to original posting.

 

Straight alcohol through the engine eh? That cleans out little nasties in the engine better then seafoam? Or are you telling me to put alcohol in my gas tank b4 I take it to get smogged?

[porcupine73]

I've heard putting in lots of isopropyl before the smog test can help pass. Never needed to try it so I don't know if it works.

[jon38iowa]

Sorry I added that information to original posting.

 

Straight alcohol through the engine eh? That cleans out little nasties in the engine better then seafoam? Or are you telling me to put alcohol in my gas tank b4 I take it to get smogged?

I don't see airfilter or pcv valve replacement on your list. I recomend changing these as well, that is if you haven't done so.

[hankosolder2]

If your have any other suggestions as to what I can do plz let me know.

 

Also I have noticed that the car temp sensor seems to warm up pretty fast it's fully warm in like 2 minutes of driving lightly. Is it possable a fualty temp sensor can cause all these problems?

 

 

Thanks in advance

 

You could have a faulty coolant temp sensor. Check with an ohmmeter or just replace.

You could have a dribbling injector(s)...from the readings, it seems to be running rich at idle. A dribbling injector would be more of a problem at low RPMs; at wider throttle openings and higher RPMs, a small steady leak from an injector would be swamped out.

Never heard of this on Subarus, but a faulty fuel pressure regulator or leaking vacuum hose to the fuel pressure regulator could cause problems.

Any trouble codes stored?

Compression test OK?

 

Good luck,

Nathan

[gyuunuuya]

I don't see airfilter or pcv valve replacement on your list. I recomend changing these as well, that is if you haven't done so.

 

Airfilter was changed too thxs I'll add that to my list.

 

 

Where is PCV valve? anyone know or have a picture? What does it do?

DOes it have alot to do with gas mileage?

[jon38iowa]

Airfilter was changed too thxs I'll add that to my list.

 

 

Where is PCV valve? anyone know or have a picture? What does it do?

DOes it have alot to do with gas mileage?

The pcv is a component part of the engines ventilation system, moreover, if it is old or not working properly, it may affect performance.

I am not certain where your is, mine ( 2.5) is to the left of the intake and is near the bottom of a large rubber connecting hose. It costs roughly $10.00

[gyuunuuya]

The pcv is a component part of the engines ventilation system, moreover, if it is old or not working properly, it may affect performance.

I am not certain where your is, mine ( 2.5) is to the left of the intake and is near the bottom of a large rubber connecting hose. It costs roughly $10.00

 

 

Cool thanks alot guys I'll try this. So other people out thetre have gotten 12 MPG because of this valve?

 

I just came back from the auto store with the hanes manuel so I will look in there for where this valve is.

[porcupine73]

Does your vehicle seem to have a lot of rolling resistance or anything? I'm assuming you probably had to pass the smog test running on a dyno (since you're in CA)?

 

Here's where the PCV valve is on my '96. It screws in; it's not a push in type.

[OB99W]

Filled with 91 octane from Exxon

 

Gas mileage has always been horrable on the car not bad, I mean horrable like 12 MPG, with a light foot

92 Subaru legacy AWD non turbo wagon Automatic.

[...]

Also I have noticed that the car temp sensor seems to warm up pretty fast it's fully warm in like 2 minutes of driving lightly. Is it possable a fualty temp sensor can cause all these problems?

Exactly what do you mean by "the car temp sensor seems to warm up pretty fast ..."; are you saying that the temp gauge indication comes up quickly?

 

A defective temp sensor can force the ECU to remain in open-loop mode. That will cause a continual rich idle and low-speed mixture that could result in poor gas mileage and high idle HC and CO.

 

Did you use an OEM O2 sensor? Has anyone verified that it is responding correctly?

 

A scan tool should probably be used to verify closed-loop operation after warmup and that all sensors are performing correctly.

 

There are several possible causes of high idle HC/CO beyond the ones already mentioned. Something that might help point in the right direction is idle quality. Is the idle smooth or rough; when warmed up, does the exhaust pressure seem constant, or can you detect misses?

[gyuunuuya]

Does your vehicle seem to have a lot of rolling resistance or anything? I'm assuming you probably had to pass the smog test running on a dyno (since you're in CA)?

 

Here's where the PCV valve is on my '96. It screws in; it's not a push in type.

 

 

OMG thxs alot man, and YES it seems to have some kinda wierd rolling resistance. Like when I'm driving I hear a WRRRRRRR sound coming from the tires as if I drove a big rump roast truck with dirt tires.

 

Please tell me you know how to fix this

 

I was always wondering if that was a normal sound on legacies.

[jon38iowa]

OMG thxs alot man, and YES it seems to have some kinda wierd rolling resistance. Like when I'm driving I hear a WRRRRRRR sound coming from the tires as if I drove a big rump roast truck with dirt tires.

 

Please tell me you know how to fix this

 

I was always wondering if that was a normal sound on legacies.

Changine the pcv is easy, just a wrench an a few turns and your done!

I would also recomend doing as above, and having all the sensors checked.

[gyuunuuya]

Exactly what do you mean by "the car temp sensor seems to warm up pretty fast ..."; are you saying that the temp gauge indication comes up quickly?

 

A defective temp sensor can force the ECU to remain in open-loop mode. That will cause a continual rich idle and low-speed mixture that could result in poor gas mileage and high idle HC and CO.

 

Did you use an OEM O2 sensor? Has anyone verified that it is responding correctly?

 

A scan tool should probably be used to verify closed-loop operation after warmup and that all sensors are performing correctly.

 

There are several possible causes of high idle HC/CO beyond the ones already mentioned. Something that might help point in the right direction is idle quality. Is the idle smooth or rough; when warmed up, does the exhaust pressure seem constant, or can you detect misses?

 

After running seafoam through the car last night it's improved imensly. Car is MUCH more responsive and seems to have more power.

 

I changed out the O2 sensor with a Bosch universal sensor. I'm pretty sure I hooked it up right, but you are telling me to use what tool and where do I get it from to make sure it's working properly?

 

Also the idle isn't high as far as I can tell the engine just simply runs RICH. I see no difference in loss or gain of power. The car just thinks it's gas tank is a giant slurpee and wants to drink it all up before it melts.

 

 

Exactly what do you mean by "the car temp sensor seems to warm up pretty fast ..."; are you saying that the temp gauge indication comes up quickly?

 

I changed out the thermostat last night and car still warms up quickly. By quickly I mean that if I start the car dead cold and let it idle about 2-3 minutes later the thermostat reaches the halfway mark in the dash. However I also noticed that when it does if I grab the upper radiator hose it's still cold for the next 5 minutes. Maybe this is normal but if it isn't and someone tells me it's bad maybe I should go get a new coolant sensor.

 

Ok thanks again everyone for all the great replies I'm eagerly waiting for advice.

[gyuunuuya]

Changine the pvc is easy, just a wrench an a few turns and your done!

I would also recomend doing as above, and having all the sensors checked.

 

Since the PVC valve is just a valve is it possable to run a cleaner through it?

Or is there filters and stuff in it that just simply need replacment?

[jon38iowa]

Since the PVC valve is just a valve is it possable to run a cleaner through it?

Or is there filters and stuff in it that just simply need replacment?

It is possible to clean it, though it can wear out over time.

[gyuunuuya]

It is possible to clean it, though it can wear out over time.

 

 

Yeah I just bought a new open for 2.59 at the auto store : ) .

 

Gonna go pop it in right now thxs again

[gyuunuuya]

Ok old one looked like ************, all grimey and oily.

 

Gonna have wife start checking MPG tommorrow.

 

thanks again guys and if anyone else has any ideas I'll definetly try it

[gyuunuuya]

 

Thanks in advance

You could have a faulty coolant temp sensor. Check with an ohmmeter or just replace.

You could have a dribbling injector(s)...from the readings, it seems to be running rich at idle. A dribbling injector would be more of a problem at low RPMs; at wider throttle openings and higher RPMs, a small steady leak from an injector would be swamped out.

Never heard of this on Subarus, but a faulty fuel pressure regulator or leaking vacuum hose to the fuel pressure regulator could cause problems.

Any trouble codes stored?

Compression test OK?

 

Good luck,

Nathan

 

Thanks alot man I'll have to check that coolant sensor if I can find it : )

 

With the dribbling injectors is that fixable by cleaning them up or do I need to purchase new ones?

 

Oh and no there are no trouble codes stored. If I plug in the green and black connectors under the steering wheel the CEL starts blinking but after check that on this forum it seems like that is what is supposed to happen.

 

As far as a compression test the car seems to have alot of power so I doubt it's got a bad cylinder.

 

Thanks again for all the help guys.

 

Any more suggestions? as I try the ones already given.

[gyuunuuya]

Ok it's been a day and my wife has driven bout 50 miles.

 

So far her car is the same crappy mileage as far as I can tell.

 

she hit 50 mile mark and her tank is already at 3/4 which woiuld be exactly 200 miles to the tank as usual.

 

Anyone know any way to makes sure the ECU is doing it's job correctly? Do I need to take it to the dealer to get the ECU looked at or will a normal auto shop have the proper equiptment to diagnose it properly?

[jon38iowa]

Ok it's been a day and my wife has driven bout 50 miles.

 

So far her car is the same crappy mileage as far as I can tell.

 

she hit 50 mile mark and her tank is already at 3/4 which woiuld be exactly 200 miles to the tank as usual.

 

Anyone know any way to makes sure the ECU is doing it's job correctly? Do I need to take it to the dealer to get the ECU looked at or will a normal auto shop have the proper equiptment to diagnose it properly?

Are you positive the front 02 sensor is good?

Mine went bad the fuel consumtion went way up!

[gyuunuuya]

Are you positive the front 02 sensor is good?

Mine went bad the fuel consumtion went way up!

 

 

I hooked it up myself and checked it with a DMM. But it doesn't hurt to check it again : ). I'll have to test it when I get home or something?

 

Stupid as it sounds if you had a volt meter how would you check to make sure it's functioning so I know I"m doing it correctly. Also do you think the fact that it is a universal O2 sensor that maybe my car doesn't like it.

 

Also I have no CHE lights on.

 

thanks alot Jon for all your input so far.

[gyuunuuya]

Ok I changed outr the PCV and the coolant temp sensor as well as the coolest temp sending unit underneath the temp sensor.

 

I plugged in the black connectors and got 2 error code readings

 

1 ) Bad coolant temp sensor

 

2) Bad cam angle sensor

 

anyways after I changed the coolant sensor 2 things happened.

 

1) check engine light is solid on now with no codes.

 

2) even in the cold morning if u turn the car on and drive 1 block maybe about 1/4 mile or less the car is already fully heated up. like within 1 min of starting the car.

 

Also tonight I took apart the IAC unit and noticed when I disconnected the PCV valve all the tubed are gunked up with gunk. Not like where air can't get through but nice cake build up on sides of tubing.

 

I also looked at the injector rings to see if they were leaking but I didn't see anything wrong with them.

 

Gas mileage is still crap any clues???

 

PLEASE DEAR GOD PLEASE!!!!!!!!!

[ple1ades]

I am having the same problems though I am running catless with no rear o2 sensor. I would love to improve gas milage. The smog is no problem since I am in nevada.

[Bigbusa]

My 96 obs 2.2L gets 14.5 mpg in the city. It's a horrible waste of money. CEL not on.