Horrible gas mileage!!!

[keada714]

So I realized that my m42 gets horrible gas mileage. Seems worse than my cousin suburban!! I drive about 10 mile city and 25-30 mile hwy and my tank goes from the "3/4" mark to half!! I'm guessing im getting 8 miles to the gallon, which is horse shit for a 4 cylinder vehicle.

I noticed that this car been getting bad gas mileage since I bought it. First I thought it was a fuel line from the filter to the hard lines, which was cracked and leaked a little but it is still getting bad gas mileage after replacing it. The car isn't throwing any code and I've done the stomp test showing 1444. It feels like it is running good as well. This is sad because I bought the 318is thinking i'm going to be getting better gas mileage than my old car which i was pushing 17lb of boost through... Any suggestion on what I need to be doing in order to regain some of these lost miles..

[KenC]

Did you ever get your thermostat/temp issue fixed? I'm getting 3-4mpg better after replacing mine and getting it working correctly.

At 8-10mpg you should smell raw fuel at the tail pipe.

How old is your O2 sensor? Running rich like you are will kill your cat soon too.

[keada714]

I fixed the temp. It is right at the middle mark. I dont smell raw fuel at the tail pipe, this makes me really confuse. I'm not sure of how old the o2 sensor is but wouldn't it throw a code if it was bad?

[KenC]

If your cooling system is functioning properly, then the engine should run at its optimal temperature. I suspect either a faulty AFM or a bad O2 sensor... leaning toward the latter.

[keada714]

Going to replace the o2 sensor with a 95 mustang 5.0 this weekend. Going to see if I can find a affordable AFM. Thanks for your help. I was also thinking about dropping the gas tank to change out all the lines. What do you think about that? Could those old line be culprit for the bad gas mileage?

[///digitalme]

Is your sending unit working? Fuel gauge?

[keada714]

yes. I believe the gauge is working fine. When I filled it up about 10 gallon it went from having the light on to the 3/4 mark. and then after driving the 40ish miles. It went down to the half mark.

[bmwm42]

yes. I believe the gauge is working fine. When I filled it up about 10 gallon it went from having the light on to the 3/4 mark. and then after driving the 40ish miles. It went down to the half mark.

i hope your not using that as a way to try an figure out how much mpgs your getting.

[AndrewBird]

Yeah, the gauge will tend to jump large gaps for small amounts of used fuel, then not move much for large amounts of fuel. It isn't very linear.

Fill the tank, reset the odometer, drive a bit, then refill and see how much gas you used. Then take the miles you drove and divide it by the number of gallons it took to fill it back up. Much more accurate way of calculating mileage.

[///digitalme]

Yeah, the gauge will tend to jump large gaps for small amounts of used fuel, then not move much for large amounts of fuel. It isn't very linear.

Fill the tank, reset the odometer, drive a bit, then refill and see how much gas you used. Then take the miles you drove and divide it by the number of gallons it took to fill it back up. Much more accurate way of calculating mileage.

This is what I did when I had fuel gauge problems. It turnedto be the sending unit and fuel gauge. I used to fill my tank and it would show full and then in a day it would show close to half and I would put one gallon and it would go full. I happened to notice since I overfilled it 3 times and decided to tackle it. I have 2 extra gauges if you ever need one.

[keada714]

that is how i usually calculate my gas mileage, however, I thought it was really odd that it jump from 3/4 to the half mark within 40ish miles. I'll pass on the gauge as i'm trying to find a clean cluster that works. My tach isn't working at the moment. Thanks guys.. I think i'm going to go ahead and change the o2 sensor though.

[keada714]

So I took the car for its longest trip yet about a 100 mile trip today. She doesn't over heat or anything. Runs like a champ. However, before leaving I filled the tank until it clicked and filled again when I got home. The car is getting 21 miles to the gallon. All 100 miles were driven on the freeway going roughly 65-70.

I also smogged the car today and it passed with no signs of a leaky fuel system. So my guess is the o2 sensor. Any other suggestions before I start ordering parts from pelican parts..

[twistednut]

I had the same problem when I first bought mine. Replaced the o2 sensor and nothing changed. Replaced all the vac lines and my mileage went from 22 to 29 mpg.

[bmwm42]

Order from blunt for one two yes those vac lines are a gas killer if they are leaking.

[keada714]

I've done the vaccum hose delete under the intake and replace them with new lines. Some heater house (larger one) and vac lines. I just remembered when I removed the lower intake it required me to remove some fuel lines. I believe there is two fuel line coming up form the chassis to the fuel rail.. Would it matter if I swapped those two line around? I forgot which line goes where so I just made a educated guess and left it. I was wondering if anyone have a picture of can direct me in the right direction and would this effect my gas mileage..