Took the tech for a drive said feels normal. Service manager said getting 12 highway w a 4.7 is good. And i am a mechanic have been for 15 years. Its not normal and its not that they are lazy they just wont properly try to diag the problem.

 

4.7 in something that weighs almost 3 tons is going to feel like a dog and get crappy mileage. Add 20" wheels and bigger tires and it'll be worse.

Might want to look at this thread and see what people with that motor are getting for mileage, it isn't good: http://bit.ly/OGEAVo

 

Wrong - more rim = more weight. 33" tire 17" rim combo weighs much less than a 33" tire 20" rim combo. Same reason people complain about how much their brakes suck when they go to bigger rims with the same overall diameter tire

 

Go to Ford, GM, or any other dealer for that matter, your gonna get the same service. As another poster touched on, we don't have mechanics anymore. We have "computer techs" now, which relay instructions on what to do. Its not a dodge thing, in fact its not even a north american car thing. Go to a Mitsubishi dealer, or even audi, they are gonna do the same thing. Sorry to say it, but its what the world is coming to.

Now you did upgrade rims and tires, it will affect it. Maybe not much but it would be noticeable. As another poster said, its not the size that always matters its the weight, which you have added more of. I know a few guys with lifts and those that run a huge ( like 34") with a low profile tire ALWAYS complain about SUPER low mileage. Those that are the opposite don't see it as much. As I said it might make a little difference, but probably only 1mpg. I will say tho that I have driven a 4.7, and I have owned a hemi for 5 years. Night and day difference. I will never own a 4.7 in my life, IMO those motors should go out to the back 40 and rust. The 5.7 is WAY better.

My advice is go out to another dealer, or even the same one. And take a stock 4.7 out for a spin. See if there is an actual difference, but I think you will be dissapointed. If there is that much of a difference, prove it the the service mechanic. If its that substantial they will do something about it, because they have a reference.

If not, i'm sorry but I think you might be SOL with the dealers...

 

May want to check the fuel flow and pressure under load, maybe on a dyno? I had issues with my C5 corvette and no CEL. The dealer said it was normal and I even went for a test drive with the tech and he said it was normal. They said I expected too much and wasn't used to the drive-by-wire lag. I said it was BS. I replaced the fuel filter/pressure regulator (it's one component on my year model) and the symptoms went away - night and day difference. Turns out that the closed loop computer systems can compensate a lot for low fuel flow/pressure without flagging a fault.

 

Given different reaction when cold, different fuel levels, ect should help.

Did you replace the gas cap at some point with an after market? When you have the issue, for the hell of it, remove the cap, jump in the truck and see if it has an impact.

 

Old jeep.

The tires and wheels are not the issue, as i said before ive had this problem well before i changed the whees and tires. Further, the difference in weight is a couple pounds as my wheels are aluminum. Get off the tire thing. Thats a easy out bs excuse.

I have driven another 4.7, same year identical truck. It smoked mine before i changed the wheels. Like i said before, it is a noticeable difference that happened suddenly. Not something im thinking should be better just to think it. I test drove both the hemi and mine and felt like the 4.7 had plenty of power, and i dint like the mds.

I agree, i think its dbw or fuel or tranny related. I removed the cap today and no difference. Btw some days it will run as it should, then others not.

Im taking it to a dyno tomorrow, had thought that as well. U cant argue with numbers.

 

Also. I was getting 19 mpg when it was running right. Not 10. So thats a moot point.

 

I would go with a problem with the fuel system. Your descriptions do point to this. Fuel pump, a crimp in the line, regulator, filter could cause this problem. I would pull the fuel tank and check the internal system, ( runs bad with a full tank). Check all lines and filters, make sure any electronic connections have a good contact and clean any electronic ground connections if appropriate. A fuel pump replacement might be a good shot.

Sometimes you have to shot gun the system to get to the problem.

Good luck and keep us infomed.

 

Had a friend with an '06 Hemi kinda the same issue. Tried a few things in the driveway that were either cheap or free fixes for him just to see if we could dial in the problem in before he spent money he didn't have on a mechanic. One of the things I tried was to ground the throttle body (as I've done on my own, not to fix an issue but to steady my idle and improve throttle response). Low and behold it fixed his issue.

If I'm not mistaken, the new ('08+) 4.7s are fly-by-wire too. It's a free fix if you have an 18" piece of about 12 gauge or thicker wire laying around. Worth a try anyway, can't hurt...

Here is a pic of mine, I'm using 6 gauge only because I had a pre-made one for a riding mower laying around in an un-opened bag. You don't need one that big though. Ground it to either the negative post on the battery or one of the chassis ground bolts on the side...