Thread: Need more MPG

Alright folks, ive had my 3.8 NA GT for almost 3 years now and i still have not found out why im getting such low mpg compared to everyone else. I average about 21 mpg during the summer, (19 with winter blend) which is alot of urban driving. And that is no matter how hard i drive it. The few times ive gone on the thruway, i figure i get about 26 mpg. I feel like ive gone through everything possible. Heres a list:

- Newer Cooper Tires with about 32psi in them.
- New struts/springs
- Aligned twice in the 3 years
- Seems to be no drag & every tire spins freely
- Cleaned lim with new gaskets and new uim plenum
- Cleaned throttle body, EGR system, MAF & MAP
- New upper o2 sensor; oscillates like it should.
- i believe its a 195 thermostat that was replaced when i bought it; runs at about that
- Runs at about 1500 RPMs at 45 mph


Things ive checked:
- No CEL
- Torque shows both short and long fuel trims hovering right around 0.
- Barely no knock ever.
- Timing while cruising is about 30-35.
- Torque Converter does lockup
- EGR (Duty Cycle) opens about 50% at most when accelerating and cruising.
- Manifold Pressure is at about 5 psi at idle
- MAF is at about 5 g/s when idling

I am sure i am over analysing but just somethings not right and you guys are some smart fellows.

Thank you

Originally Posted by hockeybawler

21 urban driving and 26 on the highway is bad gas mileage? That seems perfectly normal to me.

This

It's not a Honda don't expect Honda mpg. Your lead foot is gonna make the biggest difference


Sent from my iPhone using Tapatalk

Fuel pressure and regulator seemed normal when i checked that too. Sometimes it does crank longer than normal. Itll also start sometimes and the rpms bounce and even out..

A 2002 GP GT is rated 20/29. And usually those numbers are low. Everyone else appears to be always getting around 25 on here. Maybe its more of the Supercharged guys? I know someone with an 05 Impala that has the 3400 in it that gets 25 mpg easily.

If it is normal, What would you guys recommend as a mod to improve it? I was looking into a plog. There also was a guy on Facebook that was doing $75 tunes. He said he'd do alot of the basics with adjusting the timing and even shift points.

Dude you totally need to use the Ogle carburetor

my local mpg suck bad, no hwy at all, stop and go all day long, 35 mph tops for maybe a few minutes at a time. i net 14's avg on the dic.

heres the kicker, not one single mod has made them better. not even after blowing up the l67, and now running a top swapped ic'ed 3.2 pulley headers ported heads and 1.95 roller rockers.

if i hit the hwy im mid 20's all day long. local is just crap.


pull your fpr vac line, see if it smells like gas.

old o2 sensor can also hurt your mpg, some say if its got 80,000 miles or more on it to just change it as maint.

Ogle carburetor lol. Nice nice.

It does smell like gas a little. Not wet or anything though. When i checked the fuel pressure, it idles at about 42psi and increases with more throttle if i remember correctly.

It'll have a faint smell just because fuel runs through it, but if it was wet or had a strong raw fuel smell thats when it's really bad.