Anyone have ideas where to start diagnosing the cause of low mileage?
I'm getting well under 20 mpg with a 94 Taurus 3.0 wagon that runs
fine, idles beautifully, starts every time, and drives straight and
60% in-town, 40% 65 mph highway driving.
-- EEC-IV code reader returns 1-1-1 (no problems)
-- D"O" is selected on the AT, and overdrive is definitely working
-- Moderate driver, no accelerator punching -- ok, not often, anyway
-- Regular gas, no pinging and no mpg change if I go to higher grades
-- Tires at recommnded inflation (Goodyear Aquatread -- but mileage
sucked before putting them on)
-- AT AXOD-E has usual '94 troubles (when warm, occasional slam shift
at slow down followed immediately by speed-up -- such as a Yield sign
or a turnpike tool booth -- and occasional shudder)
-- No obvious gas leaks at tank or engine and no raw gas smell
-- Litte or no chance that gas is being siphoned by local teen-age
Any ideas where to look?
Try new plugs and wires if you have not done so. Check all the little
hoses under the hood for leaks. Change the fuel filter and run a few cans
of injector cleaner though it. Take off the air plenum hose and look at
MAF sensor to see if its dirty or has crud on it.
YOu did not state specifically how bad your mileage was. I think our
wagon Ave. 16/18 in town. Its got as high as 29 MPG on the road under
conditions. 20 may not be far off if you d a lot of city driving.
I would start by looking at the timing. Borrow a timing light and set to 12
deg (factory is 10) with spout disconnected. Keep advancing till it shows a
ping then decrease by one. Occasional ping is okay. Remember to reconnect
How many cold starts do you make a day?
Miles per cold start
EGR function/flow... it's basically working or you'd have a code. But are
the passges clear?
Last, Gasoline brand. I use Speedway exclusively and get 22.5 60/40 Hwy/
suburbs/many starts in a 3.8 Bird 150mil/day, and 26 in 95 3.0 Taurus 90/10
Hwy/suburb few starts 100mil/day.
Knock off two mpg for the wagon. What is the NET weight.. do you carry a lot
Generally, I keep receipts of gas sales for quantity, recording
mileage, then zero out the trip odometer with each fill-up.
Actually -- working from Bob Urz's and Backyard Mechanic's replies
(thanks), I need to check the MAF. And I need to begin recording it
afresh. I just cleared up an EGR issue (nipple broken off
solenoid/control valve, gummy EGR and malfunctionion ERG sensor, all 3
See... now you see the value of providing ALL info!
WHILE the EGR system was going bad, the fuel map probably got ALL screwed up.
Did you reset the PCM by disconnecting battery for a half hour? IIRC, you
could have reset the codes by doing readout but NOT the mapping during open
loop (warmup, WOT) operation. Thomas will correct me if I'm wrong.
Once everything is fixed, you should always do a reset.
If you dont have pinging, probably is NOT the MAF.. dirty ones typically run
Of course, it helps to know everything that's relevant... :)
As for reset -- I disconnected the battery during the EGR sensor
replacement, but probably not for half an hour. Even with my 10
thumbs, it couldn't have taken that long to pop off one tiny hose, one
electrical connector, and wedge the old sensor up and out of its
spring holder, then reverse with new sensor.
Battery disconnect during the solenoid / control replacement was a lot
longer, but the Check Engine light still yapped at me, because I had
not yet replaced the sensor. That solenoid would most easily be
changed either by removing the engine or training a small monkey whose
arms had been broken in two places...
I also used my hand code reader per its instructions to reset the
codes after sensor replacement -- with my model, you flip from TEST to
HOLD while the computer is sending initial rapid pulses during key on,
engine off testing -- I don't know from reading / mapping / open loop
/ warmup / wide-open throttle operation. Wouldn't the latter damage
On Mon, 17 Nov 2003 00:05:36 GMT, Backyard Mechanic
Sounds like Dave G got everything covered. I used to have a '94 Taurus
GL and the mileage was a little above average. I used to get up to 22 city
mpg and 27 highway mpg by using Exxon/Mobil fuel. I now drive an '02 Ford
Taurus SEL Premnium and it runs very good. I switched to Shell fuel and I
get up to 32 mpg on the highway and about 24 city mpg. That is above
Exxon/Mobil are good fuel and are not the best. They burn a lot of gas
in your car. Sunoco fuel is pretty good, you save a little gas in your car
than using Exxon/Mobil fuel. Shell fuel is probably one of the best brand
name fuel on the market. They really do save a lot of gas in your car.
Independent fuel companies such as Speedway, Paciffic, Flying J and etc. are
pretty good. We don't have that many independent fuel franchise in Vermont.
Things that can affect MPG on an otherwise good running car.
amount of weight in car.
driver with a lead foot or excessive idling
wrong size tires on car affecting odometer / speedometer
speedometer gear and / or circuit
A/C on all the time
plugged exhaust (cat converter) or intake filter
high speed driving (driving significantly over interstate speeds when car is
optimized for lower speeds)
ignition and/or cam/valve timing
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You forgot cooling issues. My '92 SHO ran rich to compensate for higher
operating temps until I replaced the radiator. I'm still not getting the
26-28mpg that other SHO owners say they get and my driving is conservative
compared to some of them.
I don't pick tires for smoothness. I usually look for handling tires. Some
tire manufacturers use compounds and tread designs that they claim will
improve mpg. Michelin claims this for their rubber compounds for some
models. Cooper user to sell a narrow high pressure (40 psi) radial that they
said enhanced MPG. For these tradeoffs I doubt they would be smooth running
tires Look at tires websites for detailed information
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