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Old 04-04-2012, 02:32 AM   #1
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Default Bad gas mileage

I have a 2001 Pontiac Grand Prix and I just started having bad gas milage and the engine light comes on. So I took it to Auto Zone and there tester they hook up to the car says it has to so with the gas cap. Its a new cap, and I dont see or smell any gas from my car. Are there any things I can try to start getting better gas milage again. I used to be able to get 250 miles per tank of gas, and lately Ive only been getting around 180 miles per tank of gas..
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Old 04-04-2012, 07:22 AM   #2
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which engine? the specific code would be helpful too there are many evap codes. sometimes the lack of mileage isnt related to the evap code, how old are your plugs, air filter and fuel filter?
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Old 04-04-2012, 09:24 AM   #3
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They probably pulled a P044X code (X can run from 0 to 9). With having just bought a new gas cap (which is probably after market, not OEM) there is a good chance the code is being thrown because your gas cap does not seal properly, but there are a number of other issues that can throw this code.
  • The gas cap is not installed or working properly
  • The purge solenoid has failed
  • The canister is plugged and not working properly
  • Damaged vacuum line
  • Damaged fuel tank pressure sensor
If you tell us the exact code they pulled, we can be more specific.

This code is not likely the cause of your fuel consumption issue. Tell us more about your car (engine, mileage, recent repairs, and operating issues) and we might be able to help you narrow it down. For example, have you ever replaced the O2 sensor?
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Old 04-05-2012, 12:58 AM   #4
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Thank you for the quick response Jwfirebird and 2kg4u.
I have a 2001 Pontiac Grand Prix, V6,3800 Series.
I changed the gas filter at the beginning of last summer, changed the fuel pump at the end of last summer, I bought a locking gas cap at the parts store last summer and the engine light never came on untill just a couple weeks ago. My cousin has the machine that Auto Zone uses, but his is a little more advanced and he was able to get the engine light to go off but then it came back on the next day. He looked under the hood and didnt see anything unusual he said..

I went back to Auto Zone tonight and had them hook up there machine and it pulled up the code P0440.
Definition: Evap (evaporative emission system) small leak/no flow condition.

Explanation: The evaporative emission system is monitored for it'* ability to hold vacuum.

Probable cause:
1. Defective or loose fuel cap
2. EVAP canister or hose cracked-not connected
3. Purge or vent solenoid defective
4. Vacuum leak at engine

1.Im not sure if it would be a loose fuel cap sence I put a new one on last year.
2. Where would I look to find the EVAP canister and where to look to see if it'* hose is cracked or not connected?
3. How to tell if the Purge or vent solenoid is defective?
4. Where would I look to see if there is a vacuum leak at engine?

Also, I changed the spark plugs last summer and my cousin said the plug wires looked ok to keep using. I changed the air filter and the oil a couple weeks ago. The engine light was already on before i changed the air filter and oil. The car has 148000 miles on it. ANd I havent never changed the O2 Sensor. My sister inlaw bought this car new and she always kept up with any maintance on it.
Any help will be appreciated....Thanks,Rob
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Old 04-05-2012, 12:59 AM   #5
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--------------------------------------------------------------------------------

Thank you for the quick response Jwfirebird and 2kg4u.
I have a 2001 Pontiac Grand Prix, V6,3800 Series.
I changed the gas filter at the beginning of last summer, changed the fuel pump at the end of last summer, I bought a locking gas cap at the parts store last summer and the engine light never came on untill just a couple weeks ago. My cousin has the machine that Auto Zone uses, but his is a little more advanced and he was able to get the engine light to go off but then it came back on the next day. He looked under the hood and didnt see anything unusual he said..

I went back to Auto Zone tonight and had them hook up there machine and it pulled up the code P0440.
Definition: Evap (evaporative emission system) small leak/no flow condition.

Explanation: The evaporative emission system is monitored for it'* ability to hold vacuum.

Probable cause:
1. Defective or loose fuel cap
2. EVAP canister or hose cracked-not connected
3. Purge or vent solenoid defective
4. Vacuum leak at engine

1.Im not sure if it would be a loose fuel cap sence I put a new one on last year.
2. Where would I look to find the EVAP canister and where to look to see if it'* hose is cracked or not connected?
3. How to tell if the Purge or vent solenoid is defective?
4. Where would I look to see if there is a vacuum leak at engine?

Also, I changed the spark plugs last summer and my cousin said the plug wires looked ok to keep using. I changed the air filter and the oil a couple weeks ago. The engine light was already on before i changed the air filter and oil. The car has 148000 miles on it. ANd I havent never changed the O2 Sensor. My sister inlaw bought this car new and she always kept up with any maintance on it.
Any help will be appreciated....Thanks,Rob
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Old 04-05-2012, 07:32 AM   #6
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assuming the car is like my 03 monte was, the canister was on top of the tank. and there was an access panel in the trunk to be able to see some stuff. but i got the code on mine twice when i owned it once was the cap gasket was bad. the other was the vent valve which is on the inside of the fender kind of behind the gas filler. you can take it out and test it. take it apart and hook up some jumper wires to the battery when you have it right voltage will close it i think you wont be able to blow through it and no voltage opens it. not real sure on that but if it sticks or doesnt work at all you know thats your issue. i went and got a new one from the dealer and it didnt last a year, took it back apart and soaked it with wd40 actuated it a dozen times and never had another issue. if its not that post back and we'll try something different
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Old 04-05-2012, 09:20 AM   #7
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Those after market locking gas caps often do not seal well to the tank. Do you have your old cap? If so, put it back on for a week to see if the code goes away.
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Old 04-05-2012, 08:23 PM   #8
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I went to Auto Zone today and they swaped me out a new standard gas cap for my locking gas cap. I went with the standard gas cap because I have a hard time unlocking the locked gas cap. After putting it on the Engine Light was still on. So I went back in to Auto Zone to ask if there machine can delete the Engine Light so I turns off so I can see if changing the gas cap was the problem. The worker in Auto Zone said that if the cas cap was the problem that the Engine Light would turn off by its self.
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Old 04-05-2012, 08:27 PM   #9
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Im not sure what your talking about with the vent valve,,, Would that be the next step on trying to pin point the problem sence the gas cap didnt make the engine light go off?? Is there a way to delete the Engine Light without using the machine like Auto Zone uses or the more better ones?
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Old 04-05-2012, 08:45 PM   #10
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The engine light won't go off immediatley. The PCM has to see it working correctly a specific number of times before it will shut the light off.
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