Thread: horrible gas mileage!

I have been recently been getting bad gas mileage on my 2003 gtp. I have changed the fuel filter and fuel pump a year in half ago. I just got done changing the spark plugs from Tr8 ngks which were to cold for my setup to a hotter TR6 plugs and I changed the O2 sensors today. It still is get around 10 to 12 mpg in town on normal driving. I don't know what else to check. Thank you!

o2 sensor possibly.

i have headers and open cone intake and get up to 30mpgs on highway... 24-25 in town driving.

You can find my build thread somewhere...but I have a huge cam/heads setup with 3.29 gearing...I get over 30 mpg's quite often on the highway. Also...TR8's?

TR6's are too cold...those are for 3.2"-ish setups. Get Autolite 104's and gap em at .050". The end. See how that helps. Also...if you have headers, do you have a rear o2? If not...there is your issue.

I just put in an oxygen sensor yesterday But it did not help with any.

I'm talking rear o2

I do have a rear o2 sensor on my my headers

Thats your problem. Your car is drowning its self with fuel to try and test the cat and is seeing no response from the rear 02. Put one in and use the sparkplug non fouler trick. Also thanks for the tech tip.

Originally Posted by 01GTP

Thats your problem. Your car is drowning its self with fuel to try and test the cat and is seeing no response from the rear 02. Put one in and use the sparkplug non fouler trick. Also thanks for the tech tip.

He can't do that without a custom tune...since its an '03. He can have no cat...but NEEDS the rear o2...not a sim or fouler.

Originally Posted by bluegtp91

He can't do that without a custom tune...since its an '03. He can have no cat...but NEEDS the rear o2...not a sim or fouler.

You use the 02 with the fouler, it just pushes it out of the exhaust path more so it will see more oxygen and when the computer runs the test it will also switch to rich, it will work fine. Also this should be in the gen tech section mr. mom.... i mean mod.

I've tried the o2 with both the fouler and the sim. From my experience...it runs best with sittin' in the factory position Amsoilmang

Originally Posted by footballplaya3k

So having no cat doesn't help gas mileage on these cars? I've been running no rear o2 with no car since June on my 98, I get 16-18 city and about 30 highway.

Because you have a '98...they don't care about rear o2's, problem in question is a newer year car which the rear o2 WILL affect the MPG's.

Originally Posted by matt5112

headers will net you more.

So will a huge cam, and a huge throttle body, and bigger injectors, and ported heads, and a custom tune, and a higher gear ratio.

BAM.

Originally Posted by matt5112

Stop being sarcastic.

you know simple flow mods improve gas mileage.

You stop being serious on this imporant thing called the interwebz...but troof...headers will net you more MPG's...along with an intake and probably a pulley to boot. Problem is...your MPG's are gonna blow because your gonna be in the throttle too much listening to the M90 scream.

thats my problem

Originally Posted by bluegtp91

I've tried the o2 with both the fouler and the sim. From my experience...it runs best with sittin' in the factory position Amsoilmang

So your saying the non fouler "trick" really doenst work? I have the non-foulers on (getting about 15-16mpg city) and been debating just taking them off.