Fuel mileage is too low, even for a V8 mustang!

50specialist · Apr 14, 2008

There's something weird. My car runs excellent, but is chugging fuel like crazy. 10 to 11 miles per gallon in city. In highway it barely waists any fuel, but in stop and go traffic, it sucks. I floored the car, no black smoke, no engine miss, checked it with timing light and it was perfect at 10 degrees, no check engine light. My dad's old 89' AOD 5.0 bronco waisted two miles per gallon less in the city with 35 inch tires and 4 inch lift kit and 410 gears. Either my fuel guage is not reading perfectly, or my car is running too rich. Now I took it on the expressway and the fuel guage needle didn't move much. 34 miles and it was still at or above full. Does it have to do with the after market Pro-M 75mm mass air meter sensor?

BlownFiveLiter · Apr 14, 2008

I'd pull codes for a start. The CEL doesn't need to be illuminated for something to be amiss. I get 13-15ish around town with the mods in my signature. How old are your O2 sensors?

Mr. Rustypwnz · Apr 14, 2008

it could be the pro-m make sure its calibrated for the right injectors, advance the timing a little and that should help, and to the post above mine check the o2's...

LiquidGT · Apr 14, 2008

+1
What kind or gears do you have? 2.73's? My gauge doesnt move from full untll 35-40 miles and the Mustangs fuel gauge isnt the best, the mark below half a tank is exactly a half tank on my gauge. With the mods I have I get 15-16 mpg in cold weather, now I'm getting 17ish now that its warmer.

50specialist · Apr 14, 2008

I have 3.27 gears. I will do the oil change this weekend, so I will be buy new O2 sensors and an OBD I decoder.

50specialist · Apr 14, 2008

slow95gt said:
it could be the pro-m make sure its calibrated for the right injectors, advance the timing a little and that should help, and to the post above mine check the o2's...

The pro-m is calibrated for my stock injectors. But I don't know how old the o2 sensors are.

svtpower · Apr 14, 2008

tune up

Do a tune up if you haven't done one for awhile.

Fresh plugs, wires, cap and rotor can really do a lot.

Also what temp t-stat are you running? If you do a lot of short trips/city driving I recommend a 192deg. If you run a 160 or possibly even a 180 your car may never get up to temp on the short trips and will run rich.

Mustang5L5 · Apr 14, 2008

Driving habits??

My '03 GT can get 300 miles to a tank easy on the highway.

However if I do all city driving, i'm lucky to do 150 miles to a tank of gas. I just tend to wind the gears out and get on the throttle and the gas just gets used up

mustangfan1990 · Apr 14, 2008

my car gets 12 on the interstate I would be happy to see 12 in the city lol.

HISSIN50 · Apr 14, 2008

50specialist said:
There's something weird. My car runs excellent, but is chugging fuel like crazy. 10 to 11 miles per gallon in city. In highway it barely waists any fuel, but in stop and go traffic, it sucks. I floored the car, no black smoke, no engine miss, checked it with timing light and it was perfect at 10 degrees, no check engine light. My dad's old 89' AOD 5.0 bronco waisted two miles per gallon less in the city with 35 inch tires and 4 inch lift kit and 410 gears. Either my fuel guage is not reading perfectly, or my car is running too rich. Now I took it on the expressway and the fuel guage needle didn't move much. 34 miles and it was still at or above full. Does it have to do with the after market Pro-M 75mm mass air meter sensor?

Are you actually calculating MPG or just going off of fill-ups vs needle position on the gauge?

mike93lx · Apr 15, 2008

forget the fuel gauge. fill her up, drive a tank, and fill her back up. that is the amount that use use for the calculation. try to get as far through the tank as possible to get an accurate average.

stykthyn · Apr 15, 2008

possibly a hole in your gas tank letting moisture in? the gasket in my 02 mustang my mileage dropped in half. replaced the gasket and I am back to getting my normal mileage.

battyice · Apr 15, 2008

mike93lx said:
forget the fuel gauge. fill her up, drive a tank, and fill her back up. that is the amount that use use for the calculation. try to get as far through the tank as possible to get an accurate average.

Thank you. As he said, forget the fuel guage when you are calculating fuel economy.

MY 85 GT · Apr 15, 2008

My 85 Gt i think gets poor mileage too..i get 14.0-14.5 highway i think thats terrible...i have all new tune parts....i have timing set a little higher like 16 degress....i have a new carb...i wish i knew why i get poor gas mileage... it has 3.08's and its a 5spd...i do about 60-65 mph doing about 1900 rpm's ....

battyice · Apr 15, 2008

MY 85 GT said:
My 85 Gt i think gets poor mileage too..i get 14.0-14.5 highway i think thats terrible...i have all new tune parts....i have timing set a little higher like 16 degress....i have a new carb...i wish i knew why i get poor gas mileage... it has 3.08's and its a 5spd...i do about 60-65 mph doing about 1900 rpm's ....

You're running a 650 Edelbrock right? You may want to purchase a tuning kit for that carb and try leaning out the primaries. The edelbrocks usually run pretty good out of the box but require some tuning for optimal performance. If you aren't comfortable taking the carb apart, you can start by swapping the metering rods and see how the car behaves.

A few other questions, what are you running for a distributor? How much total advance do you run? Do you have vacuum advance on the distributor?

67coupe · Apr 15, 2008

Do what HISSIN50 suggests!

Do not buy anything until you check milage the proper way.

1) Fill up tank
2) Reset trip odometer
3) Drive until near empty
4) Fill up tank
5) Write down the amount it takes to fill the tank.
6) Write down milage on trip odometer
7) Divide step 6 by step 5. This is your mpg.

The gas gauge for these cars is not accurate at all. It errors on the side of caution.

According to the manual, the capacity is 15.4 gallons. I don't know about you, but if I fill up as soon as I get around an 1/8th tank. It only takes about 11.5 gallons to fill up. You can see how unaccurate this is.

Mustang5L5 · Apr 15, 2008

You can't go by the gauge at all. Ford gauges are actually a little odd in that they read more slowly when the tank is full. You can fill the tank and drive 75 miles and the needle will never drop. Then after a certain point, it will drop like a rock and drop more quickly as the tank empty's. Both my Mustangs are like this and every other Ford i've driven for a while has done it.

MY 85 GT · Apr 16, 2008

battyice said:
You're running a 650 Edelbrock right? You may want to purchase a tuning kit for that carb and try leaning out the primaries. The edelbrocks usually run pretty good out of the box but require some tuning for optimal performance. If you aren't comfortable taking the carb apart, you can start by swapping the metering rods and see how the car behaves.

A few other questions, what are you running for a distributor? How much total advance do you run? Do you have vacuum advance on the distributor?

I did do some tuning to the carb so far with set-up springs and metering rods...as for the Dist i have the intial set pretty hig like 16-18 degrees it doesnt seem to run good when i lower back to say 12-14 it just seems to run nice at a higher advance dont know why...lol also i bought that carb because down the road im going to be bolting on a B&M 144 blower so i thought a larger carb would be needed and the 600 cfm edelbrock was to lean in my opinion....i pulled the plugs and they were bone white...now they seem to be a more normal color.....so im guessing i will need to get an A/F gauge and do it the right way ...as far as tuning....

battyice · Apr 16, 2008

If my memory is correct, the timing on an '85 GT is controlled by the computer based on its feedback from other sensors. If the computer or some of the sensors are disconnected, the timing won't advance.

When you have the timing light on your car, move the throttle a few times to increase the engine speed and watch the timing marks. Does the timing change? If not, you found a big contributor to poor fuel economy.

MY 85 GT · Apr 16, 2008

battyice said:
If my memory is correct, the timing on an '85 GT is controlled by the computer based on its feedback from other sensors. If the computer or some of the sensors are disconnected, the timing won't advance.

When you have the timing light on your car, move the throttle a few times to increase the engine speed and watch the timing marks. Does the timing change? If not, you found a big contributor to poor fuel economy.

What computer???? it has a vac advance dist...like an older car if i disconnect the vac advance it stays were i set it when i hook it back up the mark moves only when i apply gas so i know that part is working ok....

Fuel mileage is too low, even for a V8 mustang!

50specialist

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BlownFiveLiter

have car, will race....wait, it doesn't run

Mr. Rustypwnz

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LiquidGT

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50specialist

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50specialist

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svtpower

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mustangfan1990

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"How long does it take to get help in here?

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stykthyn

I want to measure mine. It doesn't look that tall.

battyice

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MY 85 GT

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67coupe

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MY 85 GT

battyice

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MY 85 GT

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