I know there has been previous threads regarding the low MPG on these Rams. I have just done an MPG test on my 02 5.9 Ram and it's averaging 8.5 MPG!!!!!! It only averages 12MPG on the freeway!!!! I have just serviced this truck so it has new plugs, clean K&N in stock airbox, fresh Mobil 1 10w 30 and a new PCV valve. It has been probed, scanned, leak down tested, compression checked, vacuum leak checked and emission checked! I'm at a loss here! It's not that I can't afford to drive it or put fuel in it, it's just that I have better things to spend my cash on then fueling the bonuses of the oil companies chairman! When I compare it to my friends 3500 Chevy big block 4x4 truck, his truck averages 5mpg more then mine that really pisses me off!!! What the hell is going on? What else can I do to this truck? I do like the truck as it's the best looking truck on the market but something has got to give. I'm not looking for Prius (I'm not a tree hugging lesbian) fuel economy but at least let my truck be in the same field as a big block truck? After all I'm driving a small block 4x4 not a Mack!


Any ideas anyone?

 

Sounds like you pretty much covered your bases. Have you checked for a plenum leak?

I had a 5.9 in my '98 1500 4x4 RCSB and averaged about what you do, maybe a hair better, but with a lift and 35" tires. Is funny, but the Hemi has 100+ more HP and gets about 35-30% better fuel economy. I guess that's the difference 'tween an engine with currently technology it vs. one that came on the market in the early '70s...

 

No plenum leak, I looked down with a bore scope and all is good. I have a dealer sticker on the ECU that says Authorised update could this be the 'death flash'? It was done before I owned the truck. It's only in the last year that the mpg has gone down dramtically.

 

Have you tried disconnecting the battery so the ECU resets?

Also are your oxygen sensors getting coked up, or are they on their way out?

 

I'd pull of the EGR and run some cleaner through it. Also, do the seafoam trick with the pcv valve.
I'd also say the Catalytic could be getting plugged but that should set off a code.
Where are you located...NEPA???? is that North east PA?...lol??

The gas in the winter time may have more concentration of ethanol in it and that will make your mpg's suffer a little.
However, the 5.9L magnum motors are known for being very thirsty. maybe it's time to sell and buy something else? Look at it as an upgrade in both mpg's and performance!

 

I have replaced the PCV valve, no codes are being thrown up, NEPA is North East Pennsylvania and I like the 5.9 because I know the engine well and they are extremely difficult to blow up or wear out! Last winter my truck was averaging 10.5mpg this year it's 8.5mpg! I wasn't looking for speed when I bought my truck so the stock 5.9 power is more then adequate for me.

 

I never said for you to replace the pcv valve. Did you not understand what I was saying? HERE same deal for Magnum, hemi..doesn't matter

I wanted to also add that fuel injector cleaner should be done every so often as well. if your injectors have a crappy pattern, they will waste tons of gas.

 

Yes I did understand. I replaced the PCV valve two weeks ago as the old one was worn out.

 

Replacing the pcv valve is not the same as doing the Seafoam trick!

Also read above where i added.

 

My 07 hemi gets only 10.5. Sometimes i go to 9.5mpg and Im not heavy on the pedeal. And i put the highest rated gas. I feel your pain.