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Old 08-28-2013, 01:46 PM   #1
blondiez24gt
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Doing a tune-up. Couple questions.

Well I am going to be doing a tune-up on my car. Here is a list of what I am going to do. I have a question though. About a year ago I was getting 25 mpg every tank driving to and from work everyday. Recently my car has dropped to about 20-21 mpg per tank. So someone told me my O2 sensors could be causing that even though they are not popping a check engine light. So any thoughts on that would be great. Here is what I am planning on doing.

1. Denso Iridium spark plugs

2. New plug wires

3. Clean K&N air filter

4. Clean MAF sensor

5. Change oil, and filter with mobil 1 0w-30w advanced fuel economy

6. Change transmission filter, and fluid with dexron VI

7. New fuel filter

8. Maybe change O2 sensors depending on what I find out.

9. I was also thinking about getting a high flow cat......Thoughts?
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Old 08-28-2013, 02:45 PM   #2
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You have a good list, im sure you will see a MPG gain.

High flow cat wont really do much, might as well delete it if you want high flow.

As for o2, yeah it can cause mpg drop. They arent cheap, but its worth a shot to have fresh ones.
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Old 08-28-2013, 06:23 PM   #3
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The upstream O2 sensor is what effects your gas mileage. DO NOT buy a Bosch unit, they suck. Denso is your best bet.

Also: change your PCV valve while you're at it. It's a simple yet very overlooked replacement item for a tune up.
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Old 08-28-2013, 07:27 PM   #4
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Quote:
Originally Posted by [ChaosweaveR] View Post
The upstream O2 sensor is what effects your gas mileage. DO NOT buy a Bosch unit, they suck. Denso is your best bet.

Also: change your PCV valve while you're at it. It's a simple yet very overlooked replacement item for a tune up.
X2 I replaced both of mine a couple months ago when I got HORRIBLE mileage. I dont know if that was the cause or if someone possibly "borrowed" gas but I had gotten like 15 mpg that time. My mpg's have been normal ever since around 20-25 (depending on who is driving me or my wife).

It was very inexspensive and easy to do. I got my upstream O2 sensor and the PCV from rockauto as well as a few other items. They had pretty good prices and great service.
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Old 08-29-2013, 06:55 AM   #5
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So should I just replace the upstream o2 sensor then? If I were to delete the cat would that cause a check engine light?
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Old 08-29-2013, 07:10 AM   #6
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Oh, and also. I was looking at the denso Iridium spark plugs, and they say pre gapped, and they are pre gapped for .044?? I thought the grand ams were suppose to have a .060 gap?
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Old 08-29-2013, 08:15 AM   #7
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Don't remove the cat. No beneficial gains and it throws the SES light on.
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Old 08-29-2013, 09:01 AM   #8
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I agree with Chris, don't remove the cat. Not worth it for what you are trying to accomplish.
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Old 08-29-2013, 11:20 AM   #9
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Yea, I didnt have plans on removing the cat. I was planning on a high flow cat, but not right now. I am just doing a tune-up right now. Anyways. The upstream o2 is all I really have to worry about changing? Also should I gap the denso Iridium plugs to .060? They are currently .044. They said they come pre gapped.....so not sure if that is what they should be, or if they should be gapped to .060??
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Old 08-29-2013, 01:01 PM   #10
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Yes you can gap them to the specific range.
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