I am running a 2010 Ram 1500, 5.7l, 5 speed auto, 3.92 gearing. Not the mist efficient truck right from the factory I know but I have had this truck since new andit now has 153000km on it. I am finding lately my fuel economy has dropped significantly. Just trying to find out if anyone else has experienced this issue or maybe has any idea why it has dropped.

 

Replace the front O2 sensors. I think they are maintenance items at 60K or so?

 

Bigger or just heavier tires or wheels will do that. Other than that maybe the spark plugs, most anything else would throw a CEL. I'm pretty sure the o2 sensors are within calibrated ranges or they would throw a CEL. Maybe something mechanical, like the rear axle is Fd up. need more info.

 

Winter blend fuel tends to reduce mileage as well.

 

it's not the tires, they have been on the truck for about 65000km and while they did have an effect on mileage it Wasn't this bad. Was thinking I will pull the O2 sensors and see if they look fouled but I agree there is no CEL so I don't imagine that is it. As far as spark plugs I have changed them every 50 000km like the manual says.

 

O2 sensor have many failure modes that won't set a code. The PCM doesn't have the ability to 'fact check' the data it gets from them. So, if your O2s are getting old, lazy, or simply inaccurate, the PCM has no way to know that.

 

there are 2 o2 sensors per side. Pre CAT and post CAT. If one sensor is out of whack and the PCM starts commanding a richer mixture based on on that, the other 3 will read too rich and the system should flag a CEL.

 

The rear O2's only monitor catalyst efficiency. They want to see more oxygen in the exhaust stream than the pre-cat sensors. That's all they really care about. If you are running too rich, the excess fuel will be burned off in the cat, (generating a fair bit of heat....) and the rear O2 won't have a clue. If things are only a bit out of whack, the PCM won't be able to tell. If both sensors are old, slow, and inaccurate, the PCM has no way to tell, and will run the engine according to the data it is getting. There has to be a pretty significant imbalance between banks before the PCM will get the idea that something isn't quite right.....

Then sensors that are in there are 7 years old, and have over 100K miles on them. It's time for new ones.

 

I have ordered 2 new O2 sensors. I will install them when Inget them and see if it makes a difference. My assumption was that a faulty sensor would trip a code so I assumed they were good but if that is not the case then hopefully that is the gremlin and they pay for themselves with improved mileage.

 

Brand of the O2 sensors matters as well. At least, it does on the older trucks.... NTK used to be the OEM piece, and Denso worked good as well. (may have that backwards...) But, the bosch sensors, while generally cheaper than either of the other two brands, just would run right. Fuel economy was actually WORSE. No idea why, but, several trucks have seen issues with the Bosch sensors, that was eliminated by using a better brand sensor.