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DeckRSQDakota
Dodge Dakota
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9/25/2003
14:34:36

Subject: Better MPG from a 3.9L?
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Anyone have any tips on how to get better MPG from the 3.9? I've seen aftermarket air intakes on eBay, but most of 'em seem like a joke. Does a REAL cold-air intake help at all? Are there any other mods to boost the gas mileage. The truck is a '98 regular cab, 2wd, auto, 3.55 rear.

Thanks,
Eugene
1966 Chrysler NYer (fully loaded)
1973 Dodge Dart sedan /6
1998 Dakota 3.9L

www.double-yellow.com



S. Hardy
Dodge Dakota
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9/25/2003
16:21:06

RE: Better MPG from a 3.9L?
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I'm on the same quest you are.

I don't know what it is right at the moment but I'm sure it's better. The reason I don't know is the wife drove it early in the week and put gas in it and didn't write down the mileage, so now I have to go another tank full.

My starting mileage was 17.8 mpg, before any mods.

I've done a few of the simple mods so far.

General tune-up (plugs - tranny fluid and filter)
Open Air cleaner with K&N filter
Relocate AIT sensor
TPS sensor adjustment
Removed and cleaned TB

This weekend I'm going to be changing the thermostat to 180 degrees.

Just those few things have had a large impact on the performance of the truck, and I expect to see an increase in gas mileage, if the wife doesn't take the truck again.

One of the things I'm sure will get better mileage will be a bed cover. So that's on my to do list.




Demon
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9/25/2003
17:25:16

RE: Better MPG from a 3.9L?
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I have a 2000 Dakota Sport 3.9. Get 17-19 MPG regularly with in town driving. Got as much as 24 MPG on highway. I have opened up my air cleaner also and saw no change. I have done a few things that have the engine running about 5 degrees cooler, but also saw no change. Increased air intake and colder air intake improving mileage is a myth. The intake sensor will actually richen the fuel mixture to keep it consitent with the increased air flow thus reducing mileage. My mileage fluctuates continously from 17 - 19 MPG with virtually no change in my driving habits. Minor fluctations as I see are normal, and the small change will not be noticeable (depending on the amount of air intake) due to other factors that affect mileage (driving habits, weather, etc).



jeremy
Dodge Dakota
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9/25/2003
19:56:55

RE: Better MPG from a 3.9L?
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the things s hardy mentioned are pretty much it. There are more mods that will increase mpg, such as a new TB, 1.7 rockers, maybe a muffler, but if your sole purpose for buying these things is to improve mileage, then it pointless. You won't cover the cost of these things within the life of your truck. They are however a lot of fun.



Aden
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9/25/2003
20:56:14

RE: Better MPG from a 3.9L?
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tried all of these but the best so far came from
larry and krc advance timing mod
will probably net you 2mpg +some horsepower
and drivability for 1 hrs work n slashed
wrists worth the effort

01 clubcab



John M
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9/26/2003
12:19:07

RE: Better MPG from a 3.9L?
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I'd be happy to get 17 mpg. I have a 2000 Dak Sport Plus 4x4 V6 with the optional lower gear ratio. I get between 13 and 15 mpg. If I put it in 4x4, it's worse. I'm assuming it is because of the lower ratio and large tires. I have a bed cover but really didn't notice a significant improvement. Does this sound like there is a problem with my truck? Or are my conclusions about the gear ratios and tires correct? Thanks.



daveo
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9/26/2003
19:31:49

RE: Better MPG from a 3.9L?
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I have a '96 xtended cab and always get between 19-21.The only thing I've done is add a K&N drop in filter. The only thing I can figure is that I'm running 215/70-15's.
Maybe the tire size helps.(?)

Later,
Daveo.



97 V6 Dakota
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9/27/2003
22:55:05

Performance ideas?
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I have a 97 Dakota 3.9. I have just started doing some small things to it to improve performance. So far I have put a throttle body spacer on it and an intake. I am hoping to find someone that will put dual exhaust on it for me(a pipe straight from each header). I only have the stock exhaust manifolds on it now. Does anyone know a company that sells headers for the 3.9? What would be a good brand muffler to put on each exhaust pipe? I keep seeing 1.7 Rockers here in the dakota forum. What are they? (Just different rockers?) And what does the 1.7 mean? Also, what else should I do to improve performance that won't put a permanent hole in my wallet? Thanks for any feedback on my numerous questions!



nopennies
Dodge Dakota
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9/28/2003
14:40:29

RE: Better MPG from a 3.9L?
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For better gas mileage, pull the V6 and drop in a four banger.
Or strip it down to the weight of a civic.

OR get a better paying job and don't worry about it.



S. Hardy
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9/29/2003
17:58:42

RE: Better MPG from a 3.9L?
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I finally ran a tank of gas out and checked it.

I went from 17.9 before mods to 18.3 after mods.

No improvemnt there except I have a truck that runs a little stronger than when I got it.

Not done fiddling with it yet.

99 SLT V-6 Auto.
Open air cleaner with a K&N filter (S-bolt)
TPS ajusted (.73 volts)
AIT mod
180 thermostat
TB cleaning
General tune up.



jstdume
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9/30/2003
10:06:26

RE: Better MPG from a 3.9L?
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When you drop in that 180 t-stat let me know how much your gas mileage goes down due to the fact that the engine will be operating at a lower temperature and the computer will richen up the mixture and thus decrease your fuel mileage



v6Dakota
Dodge Dakota
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9/30/2003
10:44:53

RE: Better MPG from a 3.9L?
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jstdume, why would the computer richen the air/fuel mixture just because it runs a few degrees cooler?



J and J Auto
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9/30/2003
11:12:59

RE: Better MPG from a 3.9L?
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That is the nature of the beast.

Cooler engine temp or incoming air temp will
richen the mixture and advance the timing.

That is why your engine will run fast when cold

Some trucks will show an increase in mileage and
some a loss. colder plugs on a stock motor will
also drop the gas mileage.

My last check on my 95 3.9 4X4 was 22.36mpg any
way you can improve the efficiency of the motor
you will gain mileage.

Moding the crank sensor will give you better
mileage from the timing advance 1.7 rockers
will give you better mileage because you get
more air and fuel and increase efficiency. also
a bigger TB will help

once you have the intake side done the headers
will than give you more benefit and a good set
of injectors like FMS matched within 2% will
give you better mileage than the 1 hole wonders
matched within 15%

A jet stage 2 will improve gas milage by about
2 mpg

setting the injector sync to the + side will also
give you better milage.

When my truck was stock it got 17 18 mpg after
all the mods it improved a lot. Stroking the
motor will also give you better mileage

A MSD ignition will also help but you need to
open the plug gap to propogate a bigger flam front
and get more power from the same charge of
air and fuel.

Hell my built 69 road runner pulls 21 on the highway

Larry
J&J Auto

S. Hardy
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9/30/2003
17:58:26

RE: Better MPG from a 3.9L?
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Well considering everything I have done.
Knowing that a 180 degree thermostat and AIT mod would increases the fuel mixture.
My gas milage has stayed the same, but the engine runs alittle stronger.
I would say that puts me on the plus side.
And like I said, I'm not done yet.



xenon
Dodge Dakota
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10/05/2003
03:55:41

RE: Better MPG from a 3.9L?
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Hey john m. your right about the lower gear ratio and larger tires making you loose gas milage.



DL
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10/05/2003
23:42:01

RE: Better MPG from a 3.9L?
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17-19mpg I wish! I have a 95 and a 99 3.9L and both get 14mpg on the highway and always have. I burn low grade reg gas. What are the 20 mpg trucks burning?



GB2000
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10/06/2003
00:29:18

RE: Better MPG from a 3.9L?
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Vegetable oil! :)



Lou
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10/06/2003
00:34:18

RE: Better MPG from a 3.9L?
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i tried true duals on my 99 sport. dual 2 inch pipes with magnaflows and no convertors, in fact. performance went to hell along with mileage. ended up going back to the 2 1/2 single exhaust with 1 flowmaster. and yes i had the 02 simmulator on with the duals in case anyone was wondering.



John M
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10/06/2003
07:54:24

RE: Better MPG from a 3.9L?
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Thanks for your reply Xenon. I guess there isn't too much I can do about the lower gears - but the tires do need to be replaced soon. I'm seriously thinking of getting something that is designed more for highway use and less off-road. Hopefully it will offer less rolling resistance on the road. I love this trucks hauling and towing capabilities but hate the lack of gas-mileage!!



DakDude
Dodge Dakota
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10/06/2003
10:35:11

RE: Better MPG from a 3.9L?
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I bought an 01 3.9 QC 4x4 4 months ago and had been getting 16-18mpg reliably with it. Tried the cold air route and didn't notice any difference. I removed it and went back to stock to see if I could notice a difference going the other way. None. Just had all the fluids changed in it, oil, differential, transfer case, etc. and it now gets 18-20 mpg. Yee-Haw.



J and J Auto
GenII
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10/06/2003
14:37:33

RE: Better MPG from a 3.9L?
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On my truck I have no option but 92 93 fuel.

Mopar PCM 3 degrees advance on crank sensor and
10 to 1 comp with the stroker crank.

And I still get a little ping on hot days, if I
back off on the crank sensor the ping goes away
but my mileage and low end power drops off

I just don't get to wild when its 80 and above
and I am fine.

Changing to all synthetic fluids will also help
gas mileage

Larry
J&J Auto

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