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Old 02-01-2011, 11:10 AM
 
Location: Bothell, Washington
2,813 posts, read 5,600,072 times
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My wife has a 2001 Chevy Prizm, which as you probably know is just a Chevy branded Toyota Corolla.
Anyway, it has the 3 speed automatic, generally gets close to 35 MPG on the highway and about 27 MPG in town. She has 120K miles on it, and has been pretty consistent with that mileage until just the last couple of months. Now in town she is seeing only around 20-22 MPG, which seems jsut ridiculous for a car this small. Her driving habits are no different, all she does is drive the same route to and from work. It seems to run fine, no hesitation or lack of power, so I wouldn't think there was any problem with the injectors. Any ideas what would cause this? Would it be a good idea to have the spark plugs and wires replaced? The plugs were replaced 3 years ago (which for her light driving was only about 15K miles ago), if that matters.
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Old 02-01-2011, 11:28 AM
 
Location: Pomona
1,955 posts, read 10,948,301 times
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How long does it take to warm up? When cold, fuel consumption increases for better drivability. If the engine stays cold (possibly stuck thermostat), that would explain the drop in MPGs.

If you have a code scanner, run a scan too. There may be codes set for aspects that can relate to this, even though the check-engine light isn't on, ie. when a sensor is still functional but "lazy".
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Old 02-01-2011, 12:48 PM
 
Location: Bothell, Washington
2,813 posts, read 5,600,072 times
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Quote:
Originally Posted by Narfcake View Post
How long does it take to warm up? When cold, fuel consumption increases for better drivability. If the engine stays cold (possibly stuck thermostat), that would explain the drop in MPGs.

If you have a code scanner, run a scan too. There may be codes set for aspects that can relate to this, even though the check-engine light isn't on, ie. when a sensor is still functional but "lazy".
Good question- she starts the car and only drives about 8 or 9 minutes to work, so the car doesn't really warm up much. I mean the temperature guage does get up to normal operating range pretty quickly, and the heater warms up pretty quick as normal, so I wouldn't think there is really a thermostat issue.
And regarding the scan- I'm mostly a car idiot, so I don't have any of these tools or much troubleshooting prowess, unfortunately. Good point about a possible lazy sensor, though- that is something I may have to check out.
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Old 02-01-2011, 01:22 PM
 
Location: Eastern Washington
17,114 posts, read 56,745,308 times
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Quote:
Originally Posted by jm31828 View Post
Good question- she starts the car and only drives about 8 or 9 minutes to work, so the car doesn't really warm up much. I mean the temperature guage does get up to normal operating range pretty quickly, and the heater warms up pretty quick as normal, so I wouldn't think there is really a thermostat issue.
And regarding the scan- I'm mostly a car idiot, so I don't have any of these tools or much troubleshooting prowess, unfortunately. Good point about a possible lazy sensor, though- that is something I may have to check out.
This is very abusive service for any car. You probably have considerable sludge buildup in the engine, although that's not likely to be the main problem here. Something to think about beyond the state of tune of the engine would be dragging brakes. Does the car coast freely when in neutral? Assuming the brakes don't drag, I agree with Narfcake that this bad mileage would probably mean the ECU is "seeing" a cold engine. How old is your fuel filter? A decently clean fuel filter helps MPG. This could just be a combination of old tuneup parts - fuel filter, plugs, O2 sensor, etc.
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Old 02-01-2011, 01:28 PM
 
Location: Bothell, Washington
2,813 posts, read 5,600,072 times
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Quote:
Originally Posted by M3 Mitch View Post
This is very abusive service for any car. You probably have considerable sludge buildup in the engine, although that's not likely to be the main problem here. Something to think about beyond the state of tune of the engine would be dragging brakes. Does the car coast freely when in neutral? Assuming the brakes don't drag, I agree with Narfcake that this bad mileage would probably mean the ECU is "seeing" a cold engine. How old is your fuel filter? A decently clean fuel filter helps MPG. This could just be a combination of old tuneup parts - fuel filter, plugs, O2 sensor, etc.
The car does seem to coast freely when in neutral, so I haven't noticed any signs of dragging brakes. And for the fuel filter- I had the car into a shop about 4 years ago and asked about checking the fuel filter- they said on this particular car the filter is actually inside the gas tank, and cannot be replaced. Seems odd to me, not sure what you'd do if it does start to get clogged.
Great points, I think I will take it in and have a few of these things checked out.
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Old 02-01-2011, 01:33 PM
 
Location: Eastern Washington
17,114 posts, read 56,745,308 times
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Quote:
Originally Posted by jm31828 View Post
The car does seem to coast freely when in neutral, so I haven't noticed any signs of dragging brakes. And for the fuel filter- I had the car into a shop about 4 years ago and asked about checking the fuel filter- they said on this particular car the filter is actually inside the gas tank, and cannot be replaced. Seems odd to me, not sure what you'd do if it does start to get clogged.
Great points, I think I will take it in and have a few of these things checked out.
Certain BMW "PZEV" cars have this integrated fuel tank, pump, and filter, the whole thing has to be changed when the filter finally clogs up to the tune of several thousand bucks for the parts. I hope that's not what you are up against, from what I have read the BMW PZEV cars are to be avoided because of this, but the Subaru PZEV cars are not more expensive to service. Offhand if you can't/won't DIY, Car Tender is a shop with a good reputation in the Seattle area.
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Old 02-01-2011, 01:42 PM
 
Location: Butler County Ohio and Winters in Florida
928 posts, read 2,706,261 times
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I think the fuel we are buying has something to do with it.
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Old 02-01-2011, 01:45 PM
 
Location: Bothell, Washington
2,813 posts, read 5,600,072 times
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Quote:
Originally Posted by M3 Mitch View Post
Certain BMW "PZEV" cars have this integrated fuel tank, pump, and filter, the whole thing has to be changed when the filter finally clogs up to the tune of several thousand bucks for the parts. I hope that's not what you are up against, from what I have read the BMW PZEV cars are to be avoided because of this, but the Subaru PZEV cars are not more expensive to service. Offhand if you can't/won't DIY, Car Tender is a shop with a good reputation in the Seattle area.
Thanks for the info! This car is only worth about 3-4K at this point, so I won't sweat it with the lower mileage if the only solution were to end up being a replacement of the very expensive fuel tank/filter. But I think I will get a few of the more minor things checked out to see if we can narrow it down.
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Old 02-01-2011, 01:47 PM
 
Location: Bothell, Washington
2,813 posts, read 5,600,072 times
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Quote:
Originally Posted by ghostrider7811 View Post
I think the fuel we are buying has something to do with it.
Could very well be. We buy gas wherever it is cheap- and I must admit it often ends up being at the discount places like the Fred Meyer store, 7-11, and on occasion Arco. I always figured that gas all came from the same place, but for all I know these places are watering down their gas literally.
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Old 02-01-2011, 02:11 PM
 
11,550 posts, read 52,928,448 times
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At this mileage, you're looking at the liklihood of several systems and/or sensors not functioning as well as they used to ...

1) The EGR valve may be stuck, should be replaced.

2) Oxygen sensors may be "lazy" or failing, but still giving adequate signals to the computer which doesn't trigger a fault. The system is designed to trigger "faults" which could adversely affect emissions, but not so sensitive as to trigger codes when it's simply fuel economy at risk.

3) Air filter could be restricted, should be replaced.

4) While the spark plugs are pretty new, the rest of the ignition system may be getting weak. Spark plug wires wouldn't be unusual at this mileage and age.

5) If you haven't run a fuel system cleaner through this car for a long time (if at all), then do so. I'd use a can of BG44K or Lucas Fuel system conditioner (per their dilution rate) in a full tank of gas.

6) Fuel quality will certainly affect your economy. We see a lot of fuel samples with higher than mandated alcohol blends, which adversely affect the fuel mileage of your car. Not much you can do about this except to try a different fuel supplier in your area ... you may spend a few cents more per gallon but achieve much better fuel mileage to capture a net savings per mile. Essentially, all of your gasoline comes from the same distributors, but the blend of low octane and high octane fuel with alcohol, along with the additives, can vary greatly depending upon what the retailer specifies for their product.
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