Hey guys, I have a 3400 with various mods that I have been told that help out with gas (see my sig). I commute 300 miles a week (all highway) and only get 25 mpg at best. I am not a hard driver and accelerate not too hard. Even when I accelerare like a beast, I still see 23-24 mpg. I replaced the cat, My tires are brand new and I check tire pressure monthly, car is aligned, I dont idle the car unless I am at a stop light. The does car idles smooth when it has been stopped (700-900 rpms) The belts are in good condition. I changed the oil with full synthetic, and the car has 74000 miles on it. The car does run a little hot (alil less than halfway) But I ordeded a 180* t-statThese are things that I have heard can kill mpg. Anyone know what else could be crapping my MPG? The car is rated at 31 mpg highway and I see nothing close to 30. I know that number could be glorified a lil but I still am getting crap. Let me know what could be causing the problem.

 

car's will NEVER get what they're rated for...i dont know how they come up with those #'s

how many miles do you get to a tank of gas??

on the highway (straight highway) i can get anywhere between 400-500 miles to a tank of gas and i think this is amazing...and thats going 75-90mph ...i'm sure if you went 60 the whole way i'd be getting at least 500 miles to a tank of gas on the highway every time..

in town though...i only get about 300 miles to a tank of gas...i drive a 2 min drive to work every day...and then drive around town doing deliveries every now and then when i need to...and i get about 300 miles on a tank of gas...which isn't bad..

i'm very happy with the milage...but thats coming from a truck that got 300 km (maybe 170miles) to a tank of gas that cost more to fill up and it didn't matter whether it was highway or in town

 

you could get your tires nitrogen inflated, ive heard it increases fuel economy

 

I got 24.1 mpg going up to chicago and back last weekend when i went to visit my brother and that was at 80mph with CControl on. i also run 93 octane

what type of gas do you use
also do you use Ccontrol that helps alot.

 

I just noticed you already have an intake. Howlong have you had it? Maybe it's time thefilter was cleaned?If it's a high-flow filter like a K&N it still need to be cleaned every so often.

If you replaced the cat, but haven't replaced the O2 sensors that could help. They can heavily effect fuel economy if not working properly.

Have you ever run fuel injector cleaner? I usually put a bottle in every 6k which ends up being about every oil change, on a full tank of gas. Dirty fuel injectors don't mist the fuel as well, and can hurt mileage and power. You can also take it to a shop which will remove the fuel rail and run a cleaner through it that can't be done with a store-bought bottle. That would help more, but costs more as well.

Check tire pressure. Lower pressure might give you a slightly softer ride and better grip, but at the cost of mileage. With the tires cold read the tires reccomended maximum pressure, and fill to about 3 PSI below the reccomendation. This will allow for expansion when the tires get hot, so you don't go over the max reccomendation. I've done this for years without adverse effects. The correct tires can help as well. A stiffer, touring tire usually will have lessof what they call "rolling resistance" meaning better mileage. Also, a 'low profile' tire might look cooler, but actually reduces the final gearing of the vehicle, meaning more RPM at a certain speed, meaning reduced fuel economy. The same goes for smaller wheels.

Get off the gas! I know you said that you don't floor it often, but on the highway each 5 mph over 60 usually costs you1.5-2 MPG or so... I've confirmed this myself because at 60 MPH i see 30-31 MPG and at 70 I see more like 27-28. You might get passed by a minivan and have to leave earlier, but you'll just have to accept that. I'm pretty sure the governmentallows the manufacturers to list mileage at 55 mph instead of the more common interstate/freeway speed of 65-70 mph.

A/C runningwill reduce mileage as well, but if it's AC on or windows down, the AC will actually hurt fuel economy less.

Reduce dead weight. If you've got a bunch of junk in your car and you don't need it every day, get rid of it.

Spark plugs also help a bit, old plugs don't ignite the fuel as well, meaning less power and less mileage. Plug wires also effect this, and it's actually cheaper to replace the wires than it is to have them tested.

You have synth in the engine, why not the transmission? If it's never had a tranny fluid flush done, do it, and replace it with synthetic. Certainly better lubrication can't be bad! Has the transmission been acting up? a transmission that doesn't shift properly can ruin mileage.

Check the fuel system, a very slow leak rarely leaves marks because it evaporates quickly, and might only appear when the vehicle is on (fuel line is pressurized), so it wouldn't leak unless you're moving, where you wouldn't notice a puddle accumulating or the smell of fuel lingering. I don't know if they make a leak-detect dye for fuel, but it couldn't hurt, and a quick scan with a blacklight will quickly identify the problem. You can also turn the ignition to run, without the engine actually running. This will pressurize the fuel system so you can do a walk-around and check for the smell or evident puddle of fuel.

Now, a disclaimer, I'm no mechanic, but this is stuff that I've come across when researching how to improve my own mileage, and really makes sense.

Don't put any credibility in miracle cures, a properly maintained vehicle will always produce better results than any "gas tank pill" or "intake turbulator" et all.

Plus, if you do EVERYTHING

 

Filling tires with nitrogen in and of itself doesn't improve fuel economy. Nitrogen doesn't chage in pressure as much as standard air does - If you have 30 psi it will remain at 30 psi weather hot or cold, this is the reason they do it in NASCAR and other race vehicles.

I would do a full tune up - wires, plugs, fuel filter, air filter, etc. Also do you run gas with ethenol in it? If not, run a few tanks with 10% ethenol, standard E-10. Ethenol will clean the injectors and improve gas milage. The trade off is the ethenol gives a hair less gas milage.

So I would run the E-10 for about 5 tanks worth to help clean and then switch back to your normal gas.

Also if you have the means, do a compression test on each cylinder to see if you might be loosing power somewhere and needing more gas in the other cyclinders to remain at speed.

 

Ya I drive all city, about 130 miles per week and average about 25mpg. I try to keep most shifts under 2800 RPM. If you really want to increase mileage though I have found that letting it shift at about 2200 RPM helps alot. The problem with that for me is its just too slow. I think paying attention to your engine RPMs are the best way to achieve good fuel economy

 

Very good points, I forgot to mention also watch where you're getting gas. Some places might charge a few cents less per gallon, but their fuelcan contain less of the detergents and components that help keep the fuel system clean.Like 04-Intimidator saidethanol will reduce mileage, so aside from running it to help clean the system, if you can fill up on gas with no ethanol it could help as well.E85 cars usually suffer when using E85, up to 5-10 MPG highway!

From working at a gas station I can also tell you to watch the filler trucks too. Fueling during or shortly after (like 5 minutes) the tanker drops a load is bad, because the churning of the fuel allows more contaminates to be pumped. You shouldn't have to worry about waiting 5 minutes every time you fuel though, they have to leave a receipt, get a signature, etc.and almost always hang around for 5 minutes after the delivery just to get some coffee or whatever.

 

i get 300 miles to a tank on the highway. Everything you have said for me to fix, I already do. I have not tried any fuel injector cleaner, but I have filled up with gas with 10% ethanol for a couple fills ina row at one point. I have a hunchit is a dirty maf sensor or a dirty o2 sensor.

 

I do mixed driving and I'm averaging around 26.3mpg. What made the biggest difference for me was driving habbits. Its hard to not get into the car, but it gave me around 4mpg improvement when I drive like a granny.


Steve