I have a 2003 Ram that has the 3.7L in it. I drive 40 miles round trip to work and am very easy on the throttle. My old 2003 QC with the 4.7 got 2/mpg in these driving conditions, but I cant squeeze more than 13, sometimes 14, out of this truck. So far I've replaced the O2 sensor and spark plugs, need some advice. Only CEL that is on is the evap system code.

 

The 4.7 got 20 mpg I meant to say

 

How are you determining the mileage?

 

Run some Seafoam or Startron through your fuel tank on the next fillup

 

I second the fuel system cleaner, try techron concentrate. Is your truck a manual or auto and how is it running? I'm chasing crappy mileage on my 3.7 as well, I used to be able to get 20-21 mpg and now I'm down to a consistent 15-16. I'm about to try O2 sensors on mine as well.

 

If you consider the curb weight of the truck to engine size it should be rather obvious. Also take a look at where the rpm range where the 3.7L makes it's power and torque as compared to the 4.7L. Heavy truck with small engine = poor mpg.

3.7L - Producing 210 horsepower at 5,200 rpm, with 235 lb-ft of torque at 4,000 rpm

4.7L - Horsepower: 235 hp @ 4800 rpm - Torque: 295 ft-lbs. @ 3200 rpm

 

Not at all true, I used to consistently get 18-21 mpg from my 3.7 ram. There is an issue here, my mileage has dropped to 15-16mpg and I've tried almost everything I can think of to fix it. OP I hope you find the answer b/c you're not the only one w/ this issue.

 

Honestly, you will get far WORSE fuel economy with an underpowered vehicle than an overpowered one.
I had a company owned truck with a job I had in the mid '90s that was a Ford Ranger extended cab with a paltry 2.3L 4 banger in it. Only thing added was a light aluminum bed cap. At least Furd was smart enough not to even offer an auto tranny with the 4 cylinder, but I NEVER got more than 15 mpg out of it! Only about 200 lbs in repair parts in the bed (about the weight of a passenger) and I'd watch it go down to 13 mpg.

Evap leak could sap a mpg or two, but not a lot. Short of keeping up with maintenance the only thing I could suggest would be to pull the parasitic clutch fan and install an e-fan, should give you a couple of MPGs in town anyway. The clutch fan pulls about 14-18 HP from the engine, not a lot for a big V8, but might be the difference between poor and halfway decent fuel economy on a V6...

 

I'll run seafoam through it tomorrow and see what happens, it's an automatic and runs great!! Gets up and goes when needed, no misfiring, etc.

 

I looked at your cardomain and noticed you have 20's on the truck, that can account for some of you mpg loss. I'm not sure how much, I've only run 17's on mine. I assume you replaced the precat sensor on your truck, correct?