I have a 01 Ram 1500 with 5.9 and have recently noticed my mileage down to 10 mpg from my usual 13. I replaced spark plugs, cap and rotor and cleaned K&N air cleaner (wasn't really dirty). I tested the wires and they are ok. Truck has approximately 34,000 mile in it and I have always changed the oil and filter every three months regardless of mileage. Tire pressure is 35 and I have also used Lucas injector cleaner in fuel. I check the MPG everytime I get a full tank. The "check engine" light is not on. I am thinking it might be a oxygen sensor, but wouldn't the "check engine" be on if a sensor is bad? Besides, should these sensors not last longer? Oh, I have not noticed any miss or hesitation at all. The truck runs just as good as when I bought it. Any suggestions are appreciated.

 

My bet is you got some of the blended gasoline - like E85 , some of the blends are up to 15 % methanol- I put some in my `06 Charger and I lost milage , still had the pep and all just worse milage.

 

I just got my 98 out of th shop, the o2 sensor was bad and the light was not on, I was getting 175 miles per tank with the 5.2, it even burned up a brand new dual inlet dual outlet cat. I had it replaced and took it to the dealer now she's running good

 

I inquired about the blends being offered locally and the only blend used is the oxyginated gas blend. But, this blend has been used here during the winter months for some years now and has never been a problem, except for a few more cents per gallon. 2005titan's post confirm that the "engine check" light does not necessarily need to be on for the O2 sensor to be bad. I will replace the sensor this weekend and fill the tank again (I just filled it yesterday) and will let you all know in a week or so if the mileage has improved. This might not correct the problem, but it sure sounds encouraging. In the mean time I am open to more suggestions just in case.

This question is for 2005titan. My mileage dropped from 13 mpg to 10 in one dip and had been there for almost two months, by yesterdays calculations it was down to 9.7 mpg. I did not mention it in my initial post because I thought might not be that relevant. But I now wondering if you might have experience some type of gradual mpg loss pattern. Did you notice any pattern on mpg gradual loss. Also, did you replace the before cat sensor or the after cat sensor?

 

Well, I added the k&n intake MSD wires, MSD coil, new plugs, Optima yellow top battery, true duals with an H pipe, then I had a new 318 put in and thats when everything went to hell...lol.....I started noticing that I was not getting above 200 miles per tank and one day while towing 2 4wheelers the cat went bad(which was a $200 cat)so I had it replaced and nothing changed so finally I took it to the shop and they replaced the sensor and so far I haven't driven it but 100 miles maybe, but the power is a lot better so I'm sure the mileage will go up. It was using so much fuel that it literally burnt the cat up with unburnt fuel.....the o2 sensor was put into the H pipe right after the cat, hope this helps and you are able to figure out whats wrong...

 

the 5.2 and 5.9 motors are tricky son of a guns. my 5.2 fluctuates big time in mileage. where do you live gabriel? it could be winter gas.

 

I live in West Texas and I have been using winter gas for years without a problem.

 

check your plenum for a leak... yank off the TB and look down into the bottom of the intake, look at all the corners and see if there is any oil pooling. a light film is normal, pooling is not. if its leaking you need to replace your plenum gasket. get a felpro one... it is the best and most sucessful gasket to use.

 

I agree with Steve. A plenum leak will cause your MPG to drop like a rock. The leak will cause your internal engine vacuum to decrease and this wil lcause the MAP sensor ( Manifold air pressure ) to send lower readings to the computer which will cause the computer to make adjustments to how it makes the engine run, including length of injector fuel spray.