HELP V6 Gas mileage sucks!

Ramrod28 · #1 05-02-2009, 01:48 AM

I've go a 97 dakota 4x4 with the 3.9 in it.
I get 11.5- 12 mpg city

So far I have a CAI, throttle body spacer, fresh tune up, MSD ingnition blaster coil and a flowmaster super 44 series. I have had the whole fuel system cleaned to. There is no Cat or resonator on the truck. I keep my foot out of the skinny peddle and still get bad gas mileage. What else can I do? I'm afraid that if I replace the O2 sensors it may through a code because there is no cat.

Any help would be appreciated.

Thanks, Ramrod

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magnethead · #2 05-02-2009, 04:07 AM

those are perfectly normal numbers. stock, I'm lucky for 15.5 highway in a 4x2.

jar1zx · #3 05-02-2009, 04:08 AM

Quote:

Originally Posted by Ramrod28

I've go a 97 dakota 4x4 with the 3.9 in it.
I get 11.5- 12 mpg city

So far I have a CAI, throttle body spacer, fresh tune up, MSD ingnition blaster coil and a flowmaster super 44 series. I have had the whole fuel system cleaned to. There is no Cat or resonator on the truck. I keep my foot out of the skinny peddle and still get bad gas mileage. What else can I do? I'm afraid that if I replace the O2 sensors it may through a code because there is no cat.

Any help would be appreciated.

Thanks, Ramrod

is the 02 sensor behind the cat? if so that might be it.
i had a 94 v6 dakota that went from 17-20mpg to 10-12. lucky at same time i got this 2000 dakota and sold the old one.

f0x672 · #4 05-02-2009, 01:48 PM

3.9 v6 - small engine in a fat truck... either you love it for the reliable engine or you hate it for the piss poor fuel mileage.. cant love it and hate it at the same time.. id put the resonators and cat back on then replace the o2 sensors... these engine rely on low end torque and with a straight piped exhaust.. well you lost that low end... improves higher end torque though..

big.bryant · #5 05-02-2009, 04:13 PM

yeah straight pipes and/or catless/resenator less exhaust setups don't give the engine enough back pressure.... back pressure is what allows the o2 censors to read correctly, if the truck has straight pipes, then the exhaust is running by the sensor too quickly and causes it to think that its running wrong. the sensor then tells the computer to dump more fuel into the engine, causing it to get bad gas mileage regardless of how nice you are on the skinny pedal.

my buddy has a 4.7 in his durango with true duals. i have a muffler and still have cats. basically if we drive the same way, i get around 15-16 he gets around 10-11. this is due mainly to the o2 sensors going ape-sh*t

dodgerules86 · #6 05-02-2009, 04:54 PM

Yup, 12-13 is what my truck would get in the city. Stock '96 4x4.
It's a Dodge truck, everyone knows they aren't good on gas.

Ramrod28 · #7 05-03-2009, 03:37 AM

so pretty much through the cat and resonator back on it, replace the 02 sensors and i should see better numbers right? now what if I buy a performance cat such as a magnaflow? Would that be better than OEM?

f0x672 · #8 05-03-2009, 11:45 AM

if i were going to replace my cat, id get a high flow from magnaflow... its more free flowing but still gives some resistance in the system to give you some low end torque

Jam1982 · #9 05-08-2009, 01:06 AM

I am not sure if this applys to the thread but.. I have 2003 Dakota 3.9l With Stock Engine I want to know if the truck runs with out the CAT?

dodgerules86 · #10 05-08-2009, 03:02 AM

Quote:

Originally Posted by Jam1982

I am not sure if this applys to the thread but.. I have 2003 Dakota 3.9l With Stock Engine I want to know if the truck runs with out the CAT?

It will run without a catalytic converter. It will probably throw a CEL.
As said above, you can get an aftermarket hi-flow CAT.

It's worth noting that it's illegal to run without a CAT.