crappy fuel mileage

[curtisparker82]

i got a 2002 zx5 automatic 106k new plugs, new wires, new coil, new air filter, new fuel filter,...it misses at idle in neutral, almost dies when you first start it when it's real cold out side...and no mater how i drive it it gets 18-19 mpg...plugs and wires are motocraft, coil is bwd, and i run 5w30 castrol full syn oil....any help is greatly appreciated thanks

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[zetecDon]

Moved to "General Technical Chat".

[Neptune15]

Over how many tanks of gas did you calculate 19 mpg?

[Magus2727]

Coil is bwd is that saying the coil pack is bad? Well you should fix that....

The the PCV tube and the connection on the coil pack.

[curtisparker82]

it's over 10-15 tanks...used reg gas and used 93 from sunoco mostly....no BWD is the brand of the coil....

[Magus2727]

Why are you using 93 octane? Have a tune or some other reason? Unless you have modified your car with a tune going with a higher grade fuel us just wasting money.

[whynotthinkwhynot]

What numbers are you using to figure fuel economy?

Usually when I see numbers this low, someone is filling up, and using gas tank capacity- 14 gal- to divide and figure fuel economy. The proper method is to fill up, hit the trip odo, then when you fill up again, divide the mileage on the trip odo by the number of gallons displayed on the gas pump.

Nearly every Focus we've asked about shows E (light comes on) when the tank has used about 10 gals leaving approximately 4 gals in reserve.

[tmittelstaedt]

I am going to guess that for some reason the engine is never moving to closed-loop operation. Drive it a while and get it nice and hot then take it to an auto parts store and have them scan it and look at all the sensor readouts and see if the engine is in closed-loop. If any of them look strange, then you may have a bad sensor.

The factory coil is going to be superior to any aftermarket coil. Get a factory coil from a wrecker and I'd bet the ilde miss goes away.

[curtisparker82]

Im running 93 cause it was getting better than 89....BEFORE WINTER I WAS GETTING 18 ON 89 AND 23-24 ON 93 THEN IT JUST DROPPED TO 18 NO MATTER HOW I DRIVE....I DROVE IT FOR A WEEK AND DIDNT LET IT REV PAST 3K AND IT ONLY GET'S 18MPG...I DRIVE THE GUTS OUT OF IT AND REV IT TO 6 BETWEEN SHIFTS AND IT GETS 18MPG...DONT MAKE SENSE ...i fill up the tank and use the miles i drove/the amount of fuel i put in the tank....

[Magus2727]

you use the same station, same pump, and let it auto kick off with out topping off?

going from 250 miles and putting in 11 gallons vs 250 and putting in 12 gallons is a difference between 22.72 and 20.8 basically a 2 MPG drop because you put a little more or less fuel on each fill up.

If you saw that much of a change in your fuel economy from going from a 89 to a 93 octane (my altitude I live has offset octane levels, 89 is still a mid grade right? what were you getting on 87?) then something is wrong. the motor it self does not run any differently as it can not tell the octane nor is it tuned to advance timing to make use of higher octane. So the only reason why you would see better fuel economy is that the octane is "fixing" another problem.

What could cause this? I am not sure. Another thing to note is that most fuels have detergents in them, some more than others. you can typical get better fuel economy from Costco gas because they typically have less additives like the Chevron or Shell gas.