Fuel Economy...

CrBoy

I having a hard time with my 95 Geo Metro Lsi (1.3L 4 cyl)... I'm getting around 24MPG in the city... and, to me, that looks really bad. The fuel economy should be a lot better, right?
The engine has 89K miles on it... no water nor oil leaks... and it's not burning oil, if you know what i mean... I change the oil and the filters often (when needed, off course )

I'm a passive drive, no hard accelerations to save fuel...

Can you guys think why this economy car is NOT so economy? What can be causing this?

Please throw your knowledge this way...

audiobliss

Can't really help ya much, but from my perspective (getting 16mpg city/highway combined), 24mpg isn't bad.

bobman1235

Yeah, but for a Metro? Thta's terrible. He should be getting 30+ city. Those things weigh 6 pounds and have lawnmower engines.

Check your air filter, it may be clogged. Check your plugs - one of them might not be firing. Is it making noise? You could have an exhaust leak.

A million things can cause poor fuel economy, those are the easiest that come to mind.

CrBoy

thanks for the replies... Air filter is brand new... but the spark plugs might be effed up... what kind of noise should I look for?

the car weighs 2061.5 pounds and it does sound like a lawnmower
that's why i'm getting a VW GTI or a Jetta.

jet2001

also try some fuel injector cleaner...it's only $3-4 a bottle.

CrBoy

jet2001 wrote:

also try some fuel injector cleaner...it's only $3-4 a bottle.

Any brand in particular?

Jstas

You should check the ignition system. I'm not exactly sure what a Geo Metro has in the way or ignition but it defintly has spark plugs and they should be changed. Also, change your plug wires, they can cause all kinds of problems including poor fuel economy. If it has a distributor, change the cap and rotor. Poor connections in there reduce spark intensity and can reduce the overal efficiency of combustion.

Make sure your tires are properly inflated. Often times, people don't keep tires inflated properly and mileage and performance suffer. It would also help to grab a bottle of a fuel system cleaner and run it through the gas tank. Chnage the fuel filter before you do this though. If the fuel filter has never been changed and you run this stuff through, it can dislodge stuff that the fuel filter grabbed and clog injectors, regulators and fuel rails farther down the line.

Some other stuff you might need to have a mechanic check are the EGR system and the emissions controls systems. Both, if they are old and covered in carbon build-up, can cause not only poor running and performance but poor fuel mileage too.

That is where I would start and honestly, doing the ignition tune-up, checking tire pressure, changing the fuel filter and running the fuel system cleaner through the lines will probably solve your problems.

Jstas

CrBoy wrote:

Any brand in particular?

I've had good experiences with STP Complete Fuel System Cleaner and virtually any product from GUMOUT.

hellohello

fuel injector cleaner, try GUMOUT
make sure ur tires are properly inflated
take out anything unneccesary, any extra junk u have in the trunk, any dead bodies lodged in the chassis, even the backseat if u never haul passengers
If you have gigantic subwoofers/amps/equipment like that in there, thats extra weight too.

jet2001

Any brand in particular?

There are many brands to choose from...I try to buy from brands I know...Valvoline, Chevron, etc...but I'm sure the generic brands work as well.

hellohello

sorry to repeat Jstas, my typing is slow, and ur posts werent there when i started

CrBoy

hellohello wrote:

take out anything unneccesary, any extra junk u have in the trunk, any dead bodies lodged in the chassis, even the backseat if u never haul passengers
If you have gigantic subwoofers/amps/equipment like that in there, thats extra weight too.

I only have my Dx-12 in a sealed box and a couple of dead bodies from last night in the trunk...

Does the Fuel Injector Cleaner really work? I have heard a lot of things about those kind of products not really working...

ESavinon

Don't forget to change your oxygen sensor(s).
They're supposed to be changed every 60k miles.
What type of fuel do you use?
If you use premium on an engine that's designed for regular you'll lose some mpg.
Premium has a higher flash rate than regular.

Markymark

A lot of the stuff has already been said, EGR, gummed injectors, fouled plugs, etc... Just something of which to be mindful: look into injector cleaner for your car, I know my car cannot run injector cleaner without eroding some of the seals/gaskets. I have to pull the injectors and set them into a bowl of injector cleaner overnight.

Are you losing oil anywhere? Check the compression of the cylinders, if one is lower than the normal "range" you might have a problem.

02 sensor? It sounds as if your car might be running too rich.
Run a can of CCC (combustion chamber cleaner) through the motor to eliminate the black, sooty buildup that results from running rich, then change the plugs, oil, wires, and 02 sensor if it needs it.
You also might look for a leaking injector... an odd problem but it might be happening.
I know that my car is REALLY sensitive to tire pressure, 32psi is recommended but I run 35 in the summer. That helps a lot.

CrBoy

ESAVINON wrote:

Don't forget to change your oxygen sensor(s).
They're supposed to be changed every 60k miles.
What type of fuel do you use?
If you use premium on an engine that's designed for regular you'll lose some mpg.
Premium has a higher flash rate than regular.

You got a point right there... I use Premium fuel... it's supposed to be a "cleaner/better fuel" which is good for the engine...??? or no...???

Markymark

Running a higher octane fuel (pump fuel) will decrease mileage but it's not going to be that substantial. I get 35mpg with my car on 87 octance (SOHC) and it only goes down to 33 or so mpg with the 91 octane. So unless your car is just REALLY tempermental, I would think that there is more of a problem than just that. But you also run into the typical detonating/pinging with the wrong fuel grade.

nadams

CrBoy- your engine is not designed to run on Premium. Always run what the engine is designed for (what the owners manual calls for) unless you have a specific reason to do otherwise.

ESavinon

Markymark is right.
You should only lose a couple of miles with premium,but if your oxygen sensors
are defective,your mileage will drop significantly.

Markymark

nadams wrote:

CrBoy- your engine is not designed to run on Premium. Always run what the engine is designed for (what the owners manual calls for) unless you have a specific reason to do otherwise.

such as: higher compression (than stock), aftermarket computer that calls for it, forced induction, etc...
certain engine mods require a higher octane. **** can is not one of these.
hahah

bobman1235

Yeah, very few cars really are designed to run on premium. People t hink it's "better" because it's a higher "number", or because it's more expensive, but in reality it just depends on the car. Even my truck, whihc you would think would be higher, says use 87.

Markymark

Well, for the most part, a good rule of thumb is this: SOHC (single overhead cam) 87 octane, DOHC (dual overhead cam) 89 octane**. The reason for this has to do with the difference between the timing (between advanced and retarded) at idle, peak in the power band, and redline. It also has to do with the compression difference (in my car anyway). The compression from a DOHC is higher than an SOHC.

**naturally aspirated without internal modifications

CrBoy

I'll try regular fuel next time... I'm definately gonna buy Fuel Injector Cleaner and a can of CCC... that should help...

The real reason why I use Premium is because everybody (here in my country) says that is a cleaner fuel... I don't even now the Octane grade of the Premium Fuel I use... they (gas stations) don't provide such information

aaharvel

check the o2 sensor. but also check the master cylinder P

(edit) premium fuel CAN make a difference, but only in engines designed to run with that high an octane; certainly not a Geo Metro; regardless of how many miles have accumulated.

Jstas

Wow, sorry but I gotta stop this.

The number of cams sittin' on top of your engine has nothing to do with the level of octane you need to use. I don't know who put that idea in your head but I would lose it quickly and not listen to anything he/she is saying.

Octane ratings are dictated by ignition timing and compression ratios. Cam/valve timing only deals with fuel/air delivery. Octane ratings have nothing to do with it.

If your car is meant to run on 87, run it on 87. The ONLY reason you should be using a higher octane in an older vehicle is carbon build up. After a few hundred thousand miles, your engine's internal parts will start to build up carbon deposits. They are negligible to engine performance if the engine systems are maintained properly. If not, carbon starts to cake on and you get hot spots and decreased combustion chamber volume. This means not only does your compression ratio go up but, the carbon can create hot spots which cause uneven ignition of the air/fuel mixture. That causes pinging/knocking and misfires and is bad.

Heat is the enemy of an engine. The reason you would need to use higher octane in an engine with a higher compression ratio is to aid in heat dissapation. If you use a higher ocatne rating, your spark plug temperature range can be lower because the higher the octane, the easier it is to ignite. So high octane in high compression, high performance engines will run cooler than a lower octane. Since compression itself adds heat, the less overall heat added to the process, the lower the overall temperature. If the temperature is lower, the engine runs more efficiently and is less likely to pre-ignite (also known as pinging/knocking) or develop hot spots that also lead to pre-ignition. Also, higher octane allows the ECM to advance timing farther. This allows the air/fuel mixture to start the ignition process sooner in the compression stroke so that you get a more complete burn of the air/fuel mixture. The more complete that burn is, the higher the efficiency of the engine will be.

Running higher octane in a engine designed for a lower octane results in many problems. You may see better off-idle response and maybe more peppy acceleration but the extra power you are getting is far outweighed by the losses you are experiencing in efficiency. I can explain that too but it will honestly be too long and I don't need to hear about it. Anyhoo, the other issues with the higher octanes in engines designed for lower octanes is that the ECM may not handle it well and cause the ignition timing to be retarded and dump extra fuel in to try and keep the engine from destroying itself. This is basically called "limp home mode" and I have seen it happen to many different vehicles with fuel injection and even electronically conrtolled carburetors. That mode can be solely triggered by an octane rating that is too high. Hang around the dragstrip and watch someone dump 104 octane fuel into thier brand new Mustang GT and you'll see what happenes.



Now, the master cylinder suggestion seems silly but it is relevant and the poster should have given more info as to why as it is not readily apparent to the average guy. If the master cylinder is leaking or failing or the brake booster has a leak in it, it can cause the pressure levels in the MC to drop slightly. This causes the whole braking system to slump in a way. This causes the brake pads/shoes to drag on discs and drums which increase friction which then increases rolling resistance which reduces overall efficiency of the vehicle...especially gas mileage. However, what is more likely is a stuck or worn caliper or caliper boot that is not holding pressure properly and causing a pad to drag. If it has drum brakes, the wheel cylinder could also have an issue causing a shoe to drag. The other issue with drum brakes is that both sides are usually run off of a single circuit from the master cylinder with a proportioning valve positioned between the rear brakes and the MC. If that proportioning valve is bad, it can cause the rear brakes to drag evenly on each side and in most cases you wouldn't really notice it until it came time to get the brakes done on the rear of the car. You wouldn't notice it because one side would not be dragging more than the other and the car would not have a tendency to "pull" to the side that the brakes are dragging on. Those would be a good places to check if the basic maintenance stuff doesn't help much.

CrBoy

WOW!!! :eek:

Thanks for the post Jstas... I asked about my fuel economy issue because I don't know much about engines and I wanted to have some opinions on my problem...

As far as I understand I have to switch to Regular fuel ASAP and do a complete clean up of the injectors, right?

thanks for the effort...

PolkThug

I'll be twin-screwed in four weeks. I'll be able to pass everything, except a gas station.

PolkThug

Jstas wrote:

...because the higher the octane, the easier it is to ignite. .

Wait a sec, the higher the octane, the less septane. Septane is easier to ignite than octane.

My hypothesis is that lower octane gas can ignite easier and sometimes when you don't want it to. Under pressure, a higher octane gas will be less likely to ignite.

jdhdiggs

Yup, and higher octane burns slower=more efficient transfer of energy. Lower octane tends to explode and ignite faster/easier, higher octane goes the opposite way.

Also, I have never seen a car get worse gas mileage from a higher octane.

The rest of it looked good.

CrBoy

I'm so DAMN confused now

Markymark

PolkThug wrote:

Wait a sec, the higher the octane, the less septane. Septane is easier to ignite than octane.

My hypothesis is that lower octane gas can ignite easier and sometimes when you don't want it to. Under pressure, a higher octane gas will be less likely to ignite.

hence the reason why higher-compression engines use a higher octane.

CrBoy

so... to Premium... or not to Premium...?