Bad fuel mileage 5.7 hemi

[Conch007]

Anyone else getting less than 14mpg? My 4th gen got way better economy. I know it’s a truck and I don’t expect amazing economy, but i do expect to get what I got out of my 4th gen which was 16-17, and also does anyone have a vibration coming from the drivetrain when In 4wd hi or auto?

Yes I was getting less than 14mpg on the interstate mine has been in the shop to fix this when I get it back this week I will post the flashes that were done. It’s a known issue if your truck was built before oct 18 there’s a flash for the ecm for fuel economy as well as one for the transmission which was running at 2000 rpms at 75 it should have been around 1500 1600 rpms at that speed. As well as a flash for the noise cancellation system for lowering the base when plugged into CarPlay. Currently waiting on calipers to arrive tomarrow. So I can get my truck back. All other parts have come in they are waiting on the calipers to finish. I ordered the cab protector bed lights and off road light kit as well. I’m anxious to get it back and see if the flashes worked. My 17 with same engine same transmission same rear diff and fuel tank got 100 miles more out of a tank.

 

[Kungfubhuda]

Yes I was getting less than 14mpg on the interstate mine has been in the shop to fix this when I get it back this week I will post the flashes that were done. It’s a known issue if your truck was built before oct 18 there’s a flash for the ecm for fuel economy as well as one for the transmission which was running at 2000 rpms at 75 it should have been around 1500 1600 rpms at that speed. As well as a flash for the noise cancellation system for lowering the base when plugged into CarPlay. Currently waiting on calipers to arrive tomarrow. So I can get my truck back. All other parts have come in they are waiting on the calipers to finish. I ordered the cab protector bed lights and off road light kit as well. I’m anxious to get it back and see if the flashes worked. My 17 with same engine same transmission same rear diff and fuel tank got 100 miles more out of a tank.

My build date is exactly 10/18... so it should be up to date? Anyway to verify?

 

[Jackham]

The reason for example that none of this is helpful is some folks don't use their cruise control. Some people just bury it when accelerating. Some like the luxury of having their truck warm when they get in. If there is anything FCA would have dialed in it would be best mileage. My 2003hemi 2500 always got a consistent 14.8 mpg at 80 mph in Montana. My F150 SC ecoboost long box half ton heavy duty got just under 21 mpg on rolling hills at 68 mph. However full out at 80 mph on the interstate it gets 16.5 with its 3.73. In short. There is nothing wrong with this truck. The variation......is you.

 

[DharmaDog]

The reason for example that none of this is helpful is some folks don't use their cruise control. Some people just bury it when accelerating. Some like the luxury of having their truck warm when they get in. If there is anything FCA would have dialed in it would be best mileage. My 2003hemi 2500 always got a consistent 14.8 mpg at 80 mph in Montana. My F150 SC ecoboost long box half ton heavy duty got just under 21 mpg on rolling hills at 68 mph. However full out at 80 mph on the interstate it gets 16.5 with its 3.73. In short. There is nothing wrong with this truck. The variation......is you.

Are you suggesting that my poor mileage is caused by my driving style, or is all in my head?

I do use cruise control - a lot. I don’t bury the throttle when accelerating. I dont warm up the truck before entering. I run 89 gas. I drive pretty close to the posted limit. I coast a lot, I don’t use 4auto. I drive a pretty close to a 50/50 mix of city/hiway. I haven’t changed the ride height, tires or wheels from stock. I haven’t changed the intake, exhaust or ECU from stock. I don’t carry around extra weight in the bed. I haven’t towed yet. I don’t live in a hilly area. My tires are properly inflated. And no one else drives the truck. But trying as hard as I can, I cannot get better than 14.5 MPG AVG out of this thing.

If it’s something I’m doing, then I have no idea what it is.

This cannot be FCA dialing in the best mileage. If so, it’s pretty sad. I know its a truck, and I love it otherwise, but I was expecting to get mileage in line with what the window sticker stated.

 

[Lize]

I was thinking even with a heavy foot I'll most likely be pleased with fuel consumption when I get my truck

In UK we have 95 and 98 octane to choose from so I'll run on 95, you can get 100 or even 102 but I avoid that as its just boosted with ethanol. I used to have an old modified 3.9 V8 Range Rover with turbo which did (US) 9mpg and current 6.2 supercharged Ute does 12mpg - both lighter and smaller vehicles running on 98 octane which can be around 10% more expensive than 95.

 

[Chris]

I was thinking even with a heavy foot I'll most likely be pleased with fuel consumption when I get my truck

In UK we have 95 and 98 octane to choose from so I'll run on 95, you can get 100 or even 102 but I avoid that as its just boosted with ethanol. I used to have an old modified 3.9 V8 Range Rover with turbo which did (US) 9mpg and current 6.2 supercharged Ute does 12mpg - both lighter and smaller vehicles running on 98 octane which can be around 10% more expensive than 95.

UK uses RON, which is different then US Octane. 95 RON is roughly equivalent to between US 87 and 89 Octane.

 

[Lize]

UK uses RON, which is different then US Octane. 95 RON is roughly equivalent to between US 87 and 89 Octane.

Thanks Chris, I didn't realise that as a lot of posts referred to octane and confusingly the UK do same. I suppose people could get confused with gallons too.

Just had a quick read of this: https://www.etuners.gr/fuel/
I'm thinking I'll still be OK on 95 RON and could try the 98 to see if there is any difference.
Either way the £ per mile certainly shouldn't be worse than current!

 

[mjharden]

I’m consistently getting 12.5ish. I’m running 33.9” tires with a Ready Lift leveling kit. Seems a bit low even still. Should I mention it to the dealer?

 

[SilverSurfer15]

Is anyone hand calculating or Just going off the dash?

 

[mjharden]

Is anyone hand calculating or Just going off the dash?

I’m just going off the dash.

 

[SilverSurfer15]

Mine stays between 13-14 on dash but doesn’t feel that low to me. Probably is, I guess I could hand calculate it but haven’t cared much.

 

[dutchman187]

Yes I was getting less than 14mpg on the interstate mine has been in the shop to fix this when I get it back this week I will post the flashes that were done. It’s a known issue if your truck was built before oct 18 there’s a flash for the ecm for fuel economy as well as one for the transmission which was running at 2000 rpms at 75 it should have been around 1500 1600 rpms at that speed. As well as a flash for the noise cancellation system for lowering the base when plugged into CarPlay. Currently waiting on calipers to arrive tomarrow. So I can get my truck back. All other parts have come in they are waiting on the calipers to finish. I ordered the cab protector bed lights and off road light kit as well. I’m anxious to get it back and see if the flashes worked. My 17 with same engine same transmission same rear diff and fuel tank got 100 miles more out of a tank.

Can you tell me this flash for the ECM for fuel economy and the Trans. Mine runs at 2rpm at 75 and also is getting the poor fuel economy. I have a rental Laramie with the same 3.92 that I'm driving right now and it feels way smoother and my fuel economy is at least 3 mpg better on same routes. My build date is in September 2018.

 

[SilverSurfer15]

My truck just came back from the dealer and they didn’t do any ecm updates. Figures. AL UH BAM UH.

Btw, you can’t flash the trans to Lower rpm. I mean you can lock the converter but rpm is based on tire size, rear end gear, and transmission ratio. Can’t change any of that with a flash. The rpm for a 3.92 truck will be ~2k at 75. Not 1600. And if your converter was unlocked in 8th on the highway you would for sure know.

 

[RedRocketZ28]

My build date was July 2018 and my truck is currently getting 13.9 MPG according to my Fuely App. If there is an update for the engine then I will let my dealer know as it's there right now for a few things.

Like SilverSurfer said though, a 3.92 truck will show around 2k RPM's at 75 MPH. Nothing you can do to change that unless you change tire size or gear ratio. I have 3.92's and just attributed the horrible MPG to that. I have a loaner F250 4x4 Crew Cab with the 6.2L/6 speed combo and I am getting almost the same MPG (using the dash) as my Ram. To me that is not acceptable.

 

[SilverSurfer15]

It does seem bad. I used to drive a 09 2500HD gas 6.0L truck on 37s that could get around 12mpg if you drove it “softly”. No reason a modern half ton should only get 14

 

[RedRocketZ28]

My thoughts exactly. Now we are just coming out of winter so I am hoping to see some change for the better here soon. When I dropped my truck off at the dealer yesterday it did show 15.6 MPG and that was with about 150 miles on that tank of mostly highway runs.

 

[alow]

I just went on a good trip and averaged around 18-19 at 80-90mph. Not the greatest but not terrible. The dash seems to be pretty close to hand punching the numbers. Has anyone noticed their truck doing better in the city than on the highway? I'm around 20-22 at home doing normal city driving but admittedly at high speeds on the highway I seem to drop down a few.

 

[RedRocketZ28]

I would kill for your numbers, alow.

 

[392DCGC]

4x4 3.21 Limited eTorque w/ 22s. 1K miles in, I'm at about 17 MPG hand calculated, 87 octane, only top tier fuel. I expect it get better with summer fuel, break-in, and the fact I just filled the engine with synthetic (pretty sure factory fill is a blend). Mostly country roads and small city driving in fuel efficient manners (lots of coasting and slow acceleration). I think remote start was killing my average in the first few weeks of ownership more than anything.

Dash MPG has almost always been up to 1 MPG optimistic than my hand calcs... don't trust the dash, folks.

 

[Neokane]

5.7 4x4 crew cab. Rebel, 3.92
Here is 65 on the flattest stretch around me.