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Terrible MPG.. Any suggestions?

ddrum

ddrum

New member
-I have a 2002 GP GT and its getting 13.3 MPG :mad:
-The only thing ive done to the car to affect fuel economy
would be my rims. They are 17's with 2 inches of rubber. I know I wont get alot with those, but i would think it would be higher than 13.3 . Every 3 mile trip the fuel meter goes down a nick.

-To filter out 50% of everybodys first answers, no I dont go WOT at every light. I do drive "economically"
-I do mostly city driving
-have new air filter, and other regular maintnence
 


Yes. I reset it when i put the rims on about a month ago.
I know people who run 20's and get better gas milage.
im puzzled
 
If you are really getting 13 mpg that is awful.:( Be aware that changing your rims ( wheel OD) will change the DIC reading without properly adjusting the PCM.

That being said, here is a list of tune up items.

1) Front O2 sensor replacement
2) Spark plug replacement
3) MAF cleaning
4) Proper tire inflation (30psi bare minimum, I personally recommend about 34 psi when checking a warm tire)

If you address these areas without a change, the problem becomes a lot harder to find. Because then it could be any of a long list of insidious problems.

Good luck
 


Im getting horrible mileage to, its down to like 11.6! I tried changing my plugs,maf,font o2 and its still bad. Are you running no cat? I dono if that could have anything to do with it because its after the front o2, but I finally just threw the code for it.
 
Ricky21 said:
Im getting horrible mileage to, its down to like 11.6! I tried changing my plugs,maf,font o2 and its still bad. Are you running no cat? I dono if that could have anything to do with it because its after the front o2, but I finally just threw the code for it.
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Just a SWAG but I’d bet your problem is your spark plugs. For optimal mpg you need to run stock heat range spark plugs and T-stat. If you’re running a smaller pulley you might want to try AL605s, otherwise stick to AL606s.:th_thumbsup-wink:
 
I was thinking that, the reason I have 104s is because i plan on dropping pulleys soon and was under the impression that it wouldnt hurt for a short time
 
Ricky21 said:
I was thinking that, the reason I have 104s is because i plan on dropping pulleys soon and was under the impression that it wouldnt hurt for a short time
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:th_laugh-lol3: I knew it :th_winking:
In just going out on a limb here and am assuming you are a little mis-informed on spark plugs.
IMHO many ppl believe colder and smaller gapped plugs some how make the engine run better or have more HP. The reality is the opposite is true; you want to run the warmest and widest gap plug you can. I’m not going it the complexities of this ATM (just to add this KR ya ya blah blah spark blow out yad yad). However, at 11mpg I’d go get a set of AL606s tonight. Recovering that 12 bucks won’t take very long, so why not just do it.:th_thumbsup-wink:
 


Ricky21 said:
So those will also run fine with a smaller pulley?
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Well, if you are going to run a smaller pulley soon I would install AL605s. They will only minimally affect your MPGs, and should allow a mild pulley drop. Every engine is different, so you’re going to want to monitor your KR just as you would for any pulley drop. But man why sweat it, plugs are cheap and easy to change. Definitely keep your 104s, but also definitely change to 606/605s for time being.
 
Yea thats what Im thnking Im going pick some up right now its not like its hard to switch em out anyway thanks for the help :th_thumbsup-wink:
 
ddrum said:
other regular maintnence
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So, this means you have a fresh fuel filter; fresh, appropriate spark plugs; a recently-cleaned and functioning MAF; clean throttle body; appropriate tire pressure; properly-functioning [read: not stuck] brakes; full, happy coolant; and happy transmission fluid with a functioning 4th gear.

The only thing left would be... vacuum leak?
 
The only thing I can think of is when I had a similar issue last year in my 2000 GTP. I had no idea why I was losing mpg's but it dropped to around 14-15 average without altering anything. Turned out my thermostat died and was constantly sending a too hot signal, forcing the water pump and fans to run continuously. Once I replaced the thermostat, my MPG's went back to normal.

This was likely a unique problem, but it's worth checking.
 


i have a 2000 pontiac and i had this problem.. about 12mpg and it was because my thermostat was broken and my car wouldnt heat up, and my CAT was clogged so i had to get a new one and my problems were solved
 
With heavier rims and city driving that can badly hurt MPGs others might not get as bad of MPGs but they are doing a different drive than you. With heavier rims increasing speed is harder but maintaining speed is easy so in stop and go traffic they will hurt the most.

You said that every 3mi trip the mpgs go down, if you are doing 3mi trips the car will not fully heat up and will use more fuel.
 
Phantom said:
With heavier rims and city driving that can badly hurt MPGs others might not get as bad of MPGs but they are doing a different drive than you. With heavier rims increasing speed is harder but maintaining speed is easy so in stop and go traffic they will hurt the most.

You said that every 3mi trip the mpgs go down, if you are doing 3mi trips the car will not fully heat up and will use more fuel.
Click to expand...

This didn't make any sense. There's no excuse for a healthy NA 3800 to make 13mpg, ever. Something is broken.
 
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