2002 Camry POOR MILEAGE

Automatic, 110k miles, well maintained, dealer yesterday verified O2 sensors etc are all working, and could find nothing wrong with the vehicle. Checked
just about everything, including plugs, air filter, ad infinitum, connections, PCV valve, etc, etc, etc., including brakes.
Poor mileage (17mpg) has been going on for about a month. Was at least mid-20's before the drop.
I'm thinking: change the O2 sensor behind the catalytic, and see what that does.
Totally at a loss here.
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Bob H wrote:

Why do you think this would make a difference?
It will your money, but little else.

If you're burning E10 (90% gasoline and 10 ethanol), that can cut your mileage down by 3% or so, which would be around 0.75 mpg. Other stuff added to the gasoline to cut down on smog might be hurting the mileage, too.
I can't help but wonder, now that summer is here, if your driving habits have changed.
Make sure tires are filled with gas (air), too.
Jeff
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Did you get new tires recently? Are you sure you were getting mid-20's before the "drop"? According to the EPA, a 2002 4 cylinder automatic Camry was rated 21/29. Mid-20's seems reasonable for mixed driving. Any chance you have a brake dragging? After a long drive, feel the wheel hubs (be careful) - if one is especially hot, suspect a dragging brake. Any chance they changed the gas formulation in your area (where are you)? Any changes in your driving pattern? Notice any changes in the transmission behavior? Any chance you have a teenager? Or maybe you park your car in a vulnerable area where someone can steal gas? How good are your gas mileage records? Basing fuel mileage on a single tank average can be very misleading. You need to compute an average over 3 or more tank fulls. If your check engine light is not on, it is unlikely the problem is your engine. Do you smell "gas" when you first get out of your car or when you are driving with the windows down? A leaking connection could explain everything. Are you in a rust prone area? I've heard stories of Camry tanks rusting out on top...could let some gas slosh out, but you should smell this.

Waste of time and money. The sensor behind the catalyst is there to verify the catalytic converter is working. It is not used to adjust the fuel mixture.

Well if nothing else comes up, I'd suspect a plugged exhaust system. The dealer should be able to measure exhaust back pressure.
Here are my thoughts about the cause - most likely to least likely -
1) Poor mileage computation 2) New tires 3) dragging brake(s) 4) plugged exhaust 5) changed driving habits 6) changed gas formulation 7) slipping transmission 8) engine mechanical problem 9) fuel system leak (you should smell this) 10) someone is stealing your gas
Ed
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Have you changed the fuel filter? Have you checked the timing? Are all the sparkplug wires in good condition?
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For a 2002 car with OBDII it is very unlikely that any of these potential problems would reduce the mileage by 39% without also turning on the check engine light. My experience has been that even minor, almost undetectable miss fires will turn on the CEL. A clogged fuel filter is more likely to affect performance than fuel economy. I suppose the timing could be off, but for a car without a distributor, the only way the timing is off enough to reduce mileage by 30% is for something major to have gone wrong, and the CEL should be on in this case.
Ed
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Clay wrote:

Fuel filter does not affect gas mileage.
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Many people ignore changing the fuel filter. I listed it more as a reminder than a cure to poor gas mileage. Are all the vacuum line in place? Even if they are in place, check them for cracks. Do you have a bad wheel bearing? Are the fluid levels at the proper level in the transmission and differential? Is the transmission slipping? Is the air filter dirty? Are the spark plugs out of dirty or out of spec? Is the correct oil in the engine?
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Are you driving in drive or overdrive? Are you doing a good deal of ideling? Have your driving habits changed?
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Google shows many people are complaining of poor mileage with the 2.4L. A powertrain defect somewhere probably.

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On Jul 8, 5:12 pm, snipped-for-privacy@hotmail.com wrote:

Timing retards as the belt stretches and can cost 4mpg, it did to me...old plugs, rotor cap wires can cost 1-2 mpg. change differential and trans and motor to synthetic 5-30 mobil 1, check brakes and how wheels spin on a lift, A bad 02 sensor, fuel leak, a bad battery needing the alternator to work constantly adds load. Id start with timing and oils
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wrote:

The OP's car has a timing chain instead of a belt so that is out as a possible cause of poor fuel economy.
I believe that the 2002 Camry uses one coil per cylinder so it does not have a distributor, cap, rotor, or high-tension wires.
The OP did not mention how many miles are on the current spark plugs, and if they have over 60,000 miles on them, then they are worth checking.
I don't think the OP defined what he or she thought as "poor" mileage, but changing differential, transmission, and motor oil to synthetic probably will not make a discernable difference in fuel economy.
Dragging brakes can cause poor fuel economy, but there are generally other symptoms that accompany dragging brakes, such as pulling or drifting, noise, rapid brake lining wear, or pulsation from rotor or drum deformation.
In an OBD II compliant vehicle, an O2 sensor that is bad enough to cause a discernable deterioration in fuel economy would probably also cause the malfunction indicator light to come on.
A fuel leak is a possibility, but I have not seen one in any late-model Toyotas.
If I were checking a car for poor fuel economy, I would make sure that the car is up-to-date with periodic maintenance, including air filter and spark plugs, check manifold vacuum, check for proper tire inflation, check for dragging wheels, check the condition of the ATF, and go for a ride with the customer to get an idea of driving conditions and driving habits.
--

Ray O
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On Jul 15, 10:25 am, "Ray O" <rokigawaATtristarassociatesDOTcom> wrote:

An 02 has a chain? Chains stretch, are you saying there is no way to set timing, I do not believe that.
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wrote:

According to the faq section at Toyota's web site, the 4 cylinder engine in the 2002 Camry has a timing chain. go to www.toyota.com, and under the "About Toyota" tab, click on "Search/Help." On the Help/Search page, click on the "Frequently Asked Questions" link, and when the FAQ page comes up, enter "timing chain" in the "Search Text" field and when the answers come up, click on the "Timing Belt and Timing Chain" article. The results will show that the 2002-2007 Camry 4 cylinder has a timing chain.
As far as whether or not there is a way to set cam timing, the way to set it is to align the match marks on the camshafts and crankshaft before installing the chain. Timing chain stretch should be negligible in a 5 year old Camry, at least negligible enough to make checking the chain very low on the list of possible causes of poor fuel economy.
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Ray O
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On Jul 15, 4:11 pm, "Ray O" <rokigawaATtristarassociatesDOTcom> wrote:

Something must rotate to give firing order, I would think that there would be a way to adjust timing easily
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wrote:

The crankshaft and camshafts rotate. The variable valve timing feature on the engine makes it difficult to determine when to ignite each spark plug, so the ECU uses signals from the crankshaft and camshaft position sensors to determine when to fire. Ignition timing is not adjustable as it is controlled by the ECU. There is a spec for base ignition timing, but if it is not within spec, then the check is to see if the crank and cam position sensor gap is set correctly.
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Ray O
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Ransley; it's time to leave the hay rack and threshing machine behind.
This is modern times, the ECM computer gets a signal from the crank position sensor and cam sensors and knows where every rotating part is. It also reads manifold pressure, throtle position, vehicle speed and sets the proper timing.
Slim
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C. E. White, 7/3/2007,9:58:02 AM, wrote:

Why would this be the cause of lowered MPG?
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A change in size can throw off the odometer (it would take a major change to reduce apparent mileage by 30%). A change in type can increase rolling resistance (and decrease mileage, although not by 30%). Improper inflation of new tires can reduce mileage (but again, probably not by 30%).
I doubt new and different tires could account for a 30% change in apparent fuel economy, but it is a possibility. And just the act of subjecting your car to a tire store could indicate a cause - like for instance, while lifting your car to install the new tires they managed to crimp an exhaust pipe (and increase back pressure), or they "inspected" your brakes while installing new tires and managed to screw something up so the brakes are dragging.
Something has changed. Asking about tires is one way of smoking out what changed.
Ed
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Changing the sensor behind the cat will have zero effect on mileage. The rear sensor is not an input to the engine, its only used as a reference for converter efficiency. Did you check tire pressure? Change gas stations recently?
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Your service station could have rigged the pumps to cheat you. Happened in SoCal, about 100 stations in a chain. Pumps delivered accurate 5 and 10 gallon quantities so escaped the attention of inspectors. Any other quantity, pump indicated and customer paid for quite a bit more gas than he or she actually rec'd. Got away with it for two or three years, IIRC.
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