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Car Fuel Economy Questions and Answers This
category contains featured questions as
examples. They relate to most vehicles.
Question: 1999 Ford Taurus LX Wagon mileage 90,000 .
I am a fellow licensed mechanic, up here in Alberta. This
car was given to me with blown head gaskets. I replaced them
and new head bolts, all plugs, wires, serpentine belt, put
in new Synthetic oil like previous owner had since new. It
does not use a drop of oil and runs like a charm. It had the
engine service light on when I first restarted it, probably
from antifreeze on the O2 sensor. Replaced them and light
went out. The previous owner claimed it only got 20 MPG
since new. I have driven it through 3 tanks of gas now, and
he is right. The last tank had a new air filter in it but no
difference. It has lots of power. I believe this car would
beat my 68 Mustang with a 302 auto in a race. What do I look
for to fix this mileage problem? It has no Codes at all and
I changed everything except the fuel filter as the previous
owner changed it a month ago.
Answer: Depending upon the type of driving that
you do, twenty miles per gallon (MPG) may not be too bad.
Check with other owners of similar cars and see what kind of
mileage they are getting. If the twenty MPG is low, check
the Mass Air Flow Sensor .
Question: 1999 Lincoln Mk VIII mileage:
128,000. I have just had the transmission rebuilt in this
car and now I have developed two problems that did not exist
prior to the rebuild. The first is that I get an
intermittent "check engine" light. This comes on usually
after 3 minutes and goes off and on with no pattern as to
engine/speed. The second is that my gas mileage has gone
from 22-24 mpg avg. to 16.5 or less. The error codes and the
computer have been reset but the light keeps coming on and
the mileage is horrible. The shop replaced one of my oxygen
sensors at their expense believing they had somehow damaged
it during the rebuild. My transmission shifts as if new and
there seems to be no problem with the rebuild. The engine is
running smoothly and has plenty of power and all normal
startup computer checks read OK. Any thoughts on where to
look/things to try would be helpful.
Answer: We think you have a Mass Air
Flow Sensor that is out of range and needs to be replaced.
Question: 2001 Ford Focus, miles :
79,000. My wife contends that operating the vehicle at low
Rpms, almost to the point of lugging, results in better fuel
economy. I have been under the impression that the smaller
vehicles were to be driven at the higher RPM's to maintain
performance and minimize long term maintenance problems,
(sludge, plugged injectors, etc.). Can you help us with this
impasse?
Answer: Lugging an engine at low speeds
is not particularly good for an engine. On the other hand,
high RPM can cause accelerated wear. The key here is
moderation with regular maintenance as recommended by the
manufacturer.
Question: 2004 Honda Accord. Does
running your A/C reduce your gas mileage?
Answer: Yes it does. The
air-conditioning system uses horsepower from the engine to
run the air conditioning compressor.
Question: 1999 Nissan Altima mileage:
134,000. Since March of this year, I am keeping records of
my car's mpg averages. I began to notice a significant drop
in fuel economy. In the city, the averages were between 22
and 24 mpg, and in the highway, the average was 26 without
reaching 27. All this with new aftermarket spark plugs,
wheel alignment in all four wheels, correct cold air
pressure (32 psi front, 29 psi rear), new set of spark plug
cables, a nearly new distributor cap and rotor, and an rpm
adjust made at a local dealer. I was using an oil that
wasn't energy conserving, 15w 50 synthetic, the one I was
using since the car was new, and I decided to use 10w 30
synthetic, so fuel economy improves, and it remained the
same. Here in Puerto Rico, heat is a problem and that is why
many mechanics including dealers, use oils that aren't
energy conserving. But, well, even with the 10w 30 oil, the
problem was there. I read on the Internet, that the oxygen
sensor is related to fuel efficiency and that the best
sensors are usually replaced at 100,000 miles. So I decided
to replace the oxygen sensor with an equal aftermarket
oxygen sensor, the same one my car had since new. And, the
result was good.
The highway mileage improved, but not exactly to the
34-35 mpg average, I obtained in the past. I obtained 31.4
mpg controlling the speed, the acceleration, and the braking
in a long trip. The problem is that I still obtain between
22.5 and less than 24 mpg in the city, using the car under
the same roads I used it when it was new. This car is
capable of delivering 26-27 mpg under these conditions
because I calculated its fuel efficiency when it was new.
Some people around me say that this is not a big problem,
due to the fact that the engine has nearly 134,000 miles and
there is wear, even after using synthetic oil since the car
was new. Also, this car is automatic not standard. In spite
of this, the fact is that I am running at least 20 miles
less with each and every fuel tank, having all of the above
checked, and this happens consistently. This means more fuel
expense, and I think that probably something can be done to
put the fuel efficiency of this 1993 Nissan Sentra
(automatic) closer to where it is suppose to be, which is 26
mpg in the city and 35 mpg in the highway.
I did something that two different local Nissan dealers
did not, which was replacing the oxygen sensor for an
exactly new oxygen sensor and it worked, so that was part of
the problem. But, the car is still below its average. One
more thing is that this car had its accelerator cable
adjusted by a local mechanic, not a dealer. Can this affect
its rpm? Sometimes, after driving and for example, stopping
at a parking lot, the car seems to remain at a higher rpm
than usual, instead of reaching a lower rpm level. This
happens, but not all the time, maybe 50 percent of the time.
Other thing is that in the mornings when the car is cold, I
heard a sound similar to the one you can hear on a blender
immediately after start up, and it disappears quickly,
happening only when the car is cold. In the past, the car
made a similar sound and the starter was replaced, but
somehow, this sound is different. The catalyst hasn't been
replaced, is running with the same one it has since new. The
other thing, are well. The car runs and accelerates well,
but the accelerator feels hard when I compared with the
past. This is since the accelerator was adjusted, what
mechanics here call the accelerator leg, and other call it
the accelerator cable. I don't know if that adjustment is
making a difference, but I am going to try with other spark
plugs I have, to see if there is a difference with the ones
my car is using right now. Since I am using these spark
plugs, I haven't heard the usual engine knock that this car
makes in heavy traffic, using premium fuel all the time.
And, because the owner's manual relates the small amount of
engine knock with fuel efficiency, maybe that is another
fact.
Also, I don't know about the rest of the sensors this car
uses, (if they are working well), but I do know that there
are many other sensors or parts related. (I have the big
manual also). I don't know about the new gasoline's that are
being sold, but here in Puerto Rico everybody uses premium
93 fuel all the time. Well, that is all the information I
have. Maybe others have bigger problems, but one of the
virtues of this car is its fuel efficiency, and if it looses
it, the car looses a great part of its value. This is not a
Porsche, or a BMW M3, or one of the other monsters around,
but is a reliable car, that requires little maintenance,
and, it usually delivers better fuel than the average by
far, which I read that for 1999 the mpg average was 23.8.
Pablo in Puerto Rico
Answer: First, we would replace your
aftermarket spark plugs with the same brand that was
original equipment from the factory. There is a good chance
that your catalytic converter is partially plugged if it has
not been changed in 134,000 miles. If the timing belt has
been replaced, verify that the cam timing is correct. We
have worked on cars brought into us with complaints similar
to yours and found that the timing belt had been installed
one notch off. Rather than correcting the problem some
mechanics take a short cut and adjust the distributor to
compensate for the incorrect belt timing. This works, but
mileage is compromised. Finally, do a compression and
leak-down test to find out the condition of your engine.
Question: 2002 Ford Thunderbird mileage:
71,000. Hi guys. I have a gas consumption problem with this
car that I have had since I purchased it a year ago with
55,000 miles on it. I only get 200 miles out of a tank of
gas. It has an 18-gallon tank. This is involving mostly
expressway driving, very little city. I average around 14
mpg, which is abysmal. Taken it to several Ford dealerships,
which test and say according to their diagnostic computer, I
should be getting 26.7 mpg. The car runs perfectly, except
for an occasional shudder coming from the transmission.
There are no gas leaks at all. The dealerships don't know
what's wrong with the car, so I am hoping you can steer me
in the right direction.
Answer: Try replacing the Mass Air Flow
Sensor and the fuel filter.
Question:
2003 Ford Pickup F-150 mileage: 70,000. My truck has
two gas tanks. Front tank is slightly larger than the back.
Noticed a drop in fuel economy lately (past few months).
Started checking, front tank gets the usual 17-mpg.
Back tank varies from 11 to 13. No fuel leaks (at
least not when it is sitting in garage). No fuel
smell. Runs good. Any suggestions? I
checked your previously answered questions but didn't see
anything quite the same. Thank you for your time!
Answer: Your problem with the fuel monitoring
system, check the oxygen sensors and the mass air flow
sensor.
Question:
2001 Nissan Fronteer 2WD mileage: 67,000. Help me Bob
and Ken! I am having a TERRIBLE gas mileage problem.
In the last 8 months, my fuel economy has dropped from 16
mpg to 12 mpg! I have spent over $600 having the
problem diagnosed to no avail. Repairs that were made
include Adjust throttle linkage, Scoped and set engine,
throttle body gasket repair, timing adjusted, tune-up, new
plugs, new O2 sensor, new catalytic converter, vacuum lines
tested, emissions tested, and exhaust system check and fuel
injector cleaning. After putting the truck on 2
different diagnostic computers, at 2 different places, 2
different mechanics have stated the engine was in great
shape to have so many miles. I know that with so
many miles that I'm not going to get the same gas mileage as
I did when I bought it (24 mpg), BUT 12 MPG IS CRAZY!
Please see what you guys can come up with.
Answer:
Several things should be checked; fuel pressure regulator
and mass air flow sensor. If you have not had the
computer scanned, you should do it now having all five modes
checked.
Question:
1999 Z28 Camaro mileage: 84,000. Hi, I have a
Z28 Camaro. When I first bought the car a few years
ago, I was getting great mileage (20-25) gal. My car
has a carburetor, but has all of that emission equipment for
California. I recently changed the o� sensor, set the
timing, and adjusted the carburetor, so I was wondering what
happened to my mileage (10 miles per gallon now). So
please answer my question, and give me some info on the
computer controlled q-jets.
Answer:
Your car is equipped with a computer controlled engine
management system. An independent auto service center
can scan your computer for fault or error codes. The
information should pinpoint the malfunctioning components.
The mileage problem you are having may indicate you are
ready for major tune up.
Question:
2002 Dodge Grand Caravan mileage: 60,000. On a resent
long trip, I experienced poor fuel mileage. Before the
trip I did a tune-up, new plugs, wires, air filter, PVC etc.
Once we started, I noticed that we were getting about 23 MPG
but after 20 miles, the mileage would drop to 12 to 14.
When the engine was cold after stopping for lunch or dinner
the mileage would start at 23 then again drop to 12-14 after
20 miles. I notice the tail pipe was black.
Doing a key on engine light test, I found the following
codes. 1-2, 5-1, 5-5. This said the O� sensor
(replaced at 82K) was detecting a lean mixture. After
coming home, I took the vehicle to my local repair shop
where they could not find any codes stored. The car is
still getting poor mileage. It must be a sensor, where
should I start? Thanks, Ben
Answer: You may have a faulty oxygen sensor or
coolant temperature sensor.
Question:
1996 Pontiac Bonneville mileage: 167,000. In the past
month and a half, my mileage has gone from 450 miles per
whole tank to 300-330 per whole tank. I believe it is
a 15-16 gallon tank. At first, I thought it was due to
colder weather when I started getting about 50 miles less
per tank. But now (mid December) I am suddenly
getting 100-130 less per tank. What can I check for
and what are some possible problems that might be causing
this? Thanks!
Answer:
If a major tune-up has not been done recently, this could be
the cause of your problem. Replace the spark plugs,
plug wires, fuel and air filters, etc. Also, replace
the oxygen sensor. In addition, service the fuel
injection system. Clean the carbon deposits from the
throttle bore and idle passages. Check the
catalytic converter to make sure it is not plugged or
restricted.
Question:
1999 Dodge Neon mileage: 115,000. 5 speed. Had this
engine rebuilt at 100,000 miles about 5 years ago.
This spring, the mileage dropped from 18-20 mpg around town
to 10 mpg. New 0� sensor last spring.
Computer/ECU 2 years ago. New coolant temp sensor this
summer. Why the drop in mileage?
Answer:
Several things should be
checked; fuel pressure regulator and mass air flow sensor.
Question:
1999 Chevrolet 1500, miles: 145,000 I have replaced
plugs, alternator, belts, changed oil, cleaned injection,
and replaced fuel sensor, and my car is consuming too much
gas. It uses almost 3/4 of a tank of gas to drive 50
miles. How can I repair my car so it doesn't use so
much gas?
Answer:
Check fuel pump and Mass Air Flow Sensor.
Question:
2001 Plymouth Neon mileage: 85,000. Gas mileage has
suddenly dropped from 250 to 125 or so per tank. Some
power loss when pull off from a stop but other than that
runs well. Dealership mechanic says it checks
out OK. Sounds OK.
Answer: Check the catalytic converter to make
sure it is not “plugged” or restricted. Your car is
equipped with a computer controlled engine management
system. An independent auto service center can scan
your computer for fault or error codes. The
information should pinpoint the malfunctioning components.
Question: 1997 Jeep Wrangler,
miles: 78,200 That gets between 18-20 miles per gallon. Is
there any way to improve the mileage?
Answer: Your Jeep is equipped with
a computer controlled engine management system. The fuel
mixture is constantly monitored and adjusted for optimum
mileage and performance. The only way to improve mileage is
change driving habits i.e., slow starts, constant speeds
etc. Keeping your Jeep in top running condition also helps. 
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