I have a 95 Camry with 130,000 miles on it, recently the gas mileage has been going downhill. The tank holds 15 gallons and the last fill up did barely 300 miles, about 20mpg.... Any suggestions as to where to start? Maybe a list of things to check? I searched this group and came up with some ideas: checking an Oxygen Sensor, checking for cracks the air intake tubing, other ideas anyone? A few bits of history that might help. Several months ago I fixed a leaking fuel line (vapor return I believe, much thanks to Ray O), recently I reinstalled the oil drain pan and had to remove various exhaust parts, I was a little questionable about how snuggly I got things back together, the car doesn't sound "louder" to me, but could a "leaky" exhaust system affect the fuel economy? The service records on the car shows the spark plugs, wires, rotor, and disrupter cap all replaced within the last year. I have no idea the quality or make of the wires/plugs that were used, what are some opinions on the type/ make of the wires/plugs that should have been used? I see such a range in prices for these items, is the price for the higher quality justified, I seem to be getting mixed signals.
4 cylinder or 6 cylinder engine? Automatic or manual transmission? What is your usual MPG? What kind of driving do you do, i.e., city, highway, hilly terrain, etc.
More comments below after pertinent sections...
Did you calculate mileage by dividing miles driven by gallons filled?
A leaky exhaust generally will not cause poor fuel mileage, although you run the risk of carbon monoxide poisoning, asphyxiation, and failing emissions tests with a leaky exhaust.
The service records
I believe in using OEM ignition parts - plugs, wires, rotor, distributor (not disrupter) cap to avoid drivability problems. Some aftermarket ignition parts work fine, some do not. I don't like experimenting, so I recommend OEM. I have not seen aftermarket ignition parts cause poor fuel mileage so I doubt if that is your car's problem.
OK, now for stuff to check in the order of likely cause of the problem and ease of checking:
Check the air pressure in the tires (now is a good time to check the spare while you are at it). I recommend inflating the tires about 3 to 5 PSI over the manufacturer's recommended tire pressure to improve tire tread life and fuel economy, with the tradeoff being a slightly harsher ride. I fill the spare to the maximum listed on the tire and keep a tire pressure gauge in the car. If I have to install the spare, I can use the gauge to let air out of the spare if necessary.
Check the air filter to make sure it is not dirty. If you hold the air filter element up to a light, you should be able to see the light clearly. If the light is dim or you cannot see any light, change the air filter.
Check the mass air flow (MAF) sensor. It is the only device with wires sticking out that is attached to the air filter housing. There is a tube that protrudes into the air flowing out of the air filter, and inside the tube is a fine wire. The MAF sensor is not supposed to be serviceable, but you can try gently cleaning it with carburetor cleaner. Do not break the wire inside the tube or you will be looking for a new MAF sensor for big $$. Spray the car cleaner, let it drip dry, or maybe you can GENTLY swab it out with a q-tip.
If the MAF sensor is really greasy or oily, change the PCV valve.
My guess is that low tire pressure, a dirty air filter, and a dirty MAF sensor are combining to give poor mileage.
Check the condition of the automatic transmission fluid. It should be red and translucent. If it is black or brown or smells burnt, think about getting it changed soon. Do not get it flushed if you elect to change the ATF.
Check the brakes to make sure they are not dragging.
Check ignition base timing.
Hope this helps, let us know how things work out. Good luck!
Emissions laws - Ask the gas stations what they are selling you. If they recently started adding a lot of Ethanol to the gasoline for emissions, that will drop the BTU content per gallon of fuel and therefore the fuel mileage you can get out of said gallon - a LOT.
California had it first with MTBE, and the mileage drop was dramatic. Thanks to the Environmentalists screaming "The Sky Is Falling!" it's being expanded to other areas, though they have moved to Ethanol and away from MTBE because it's a very persistent pollutant if it gets into water sources.
Ignition parts are critical for a proper running car, they have to handle 50,000 Volts Plus reliably, and that's not easy. Coil, cap, rotor and wires (and to a lesser extent the plugs) are critical to get OEM Quality, and the only place to be absolutely sure of that is at the Dealer parts counter.
There are so many cosmetically perfect knockoffs of the name brand parts out there (complete with exact copy packaging) that they outnumber the real ones. But cosmetics don't count in critical parts, they have to work properly.
I'd have someone check over the car, hook up an old-fashioned exhaust gas analyzer and see if the mixture is right or not. -->--
I usually calculate mpg by dividing the miles driven since the last fill up by the gallons I just put in. I was not quite as scientific this time, the previous tank went full to empty for 400 miles, this last one (same driving) went 300 miles. Maybe I'm off by a bit but it is still a pretty noticeable drop.
MAF - hmmmm. When I changed the air filter on my Corolla (different car) a few months ago I did notice a wire plugged in device connected to the upper portion of the casing that clamps on top of the air filter. I did notice that this "thing" was completely missing from my Camry (subject of this post)... Now I think I'm getting somewhere here.... is the MAF a simple looking plastic plug into the side of the top of the air filter casing? Does that make sense? Which means I'm off to buy one.
"disrupter" instead of distributer.....opps! bloody spell check!
If the MAF sensor is completely missing from the Camry, I would imagine that you would get a check engine light on the dashboard, and there would be an opening in the intake in the vicinity of the air filter housing.
I don't know when the air flow sensor was changed to MAF type. The previous system had a flap that would open as air flowed past it. The previous type of air flow meter is located between the air filter housing and the intake tube.
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