Lost 4-5mpg after service

[John Casino]

I took my 2016 1500 4x4 Big Horn into the dealer 2 months ago. Had the transmission serviced as well as the 4 broken exhaust manifold bolts replaced and a new fuel pump(gauge wasn’t working). They ended up having to replace the head on the driver side because they couldn’t get a broken bolt out. After all this was done I’ve lost 4-5mpg. On trips I’ve taken before where I’ve gotten 19-20mpg I’m now getting 14-15. Any ideas on what the heck happened?!
Even on the slightest incline the truck has to down shift to hold a steady speed and the only time ECO comes on is going down a significant grade. Almost feels like I’m towing all the time.

 

[muddy12]

How many miles have you put in sense getting it back?

The computer may still be “relearning” how you drive.

I took my 2012 in for the fuel tank strap recall. When I got it back, the trans shift points were noticeably different, and there was a drop in mileage.
Step one of almost any dealer service is “disconnect the battery”. Because of this, it took almost two full weeks(due to how few miles a day I drive)for the shift points and mileage to return to normal.


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[John Casino]

I’ve done almost 8k miles since the work was done. I do a lot of driving for work. Currently headed from California out to Texas and this mileage loss is tearing me up.

 

[Pull Ya]

Did you hand calculated your mileage?
Jay

 

[John Casino]

Yes. My last fill up was 346 miles on 21.8 gallons.

 

[Sportznut]

Almost sounds like it's stuck in tow mode. Do you have a switch?

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[joshuaeb09]

If you have access to anything that can datalog I would check what the fuel trims look like for each bank since you had manifold/head work done. Should also be able to log timing advance and few other parameters, but the big red flag would be fuel trims. You can do with a tuner, but you don't have to have one to data log basic parameters. I have the older version of the trusty USB scantool with OBDwiz or whatever their free software is called. It lets me take a laptop out in most modern vehicles and log basic data for diagnostics. If the fuel trims are all jacked up it could be something as basic O2 sensors or even the MAP sensor could need replacing. Replaced the MAP sensor on my fathers higher mileage 5.7 and he noticed a difference right away last time they towed their travel trailer.

https://www.scantool.net/obdlink-sx/

 

[huntergreen]

I would go back to the dealer and see what they have to say.

 

[Burla]

winter gas.

 

[Compuls1ve]

winter gas.

I agree 100%. I lost a few MPG sometime in October and haven't gotten it back.

 

[John Casino]

I do have a tow mode switch. When I activate it the truck shifts differently and goes back when it turns off.
I wouldn’t even know where to start on fuel trims and the like, but if it came to it I’m sure I could start learning and I might, just to know.
I’ve had the truck almost 2 years now and this didn’t happen last winter, so winter gas may be a problem, but I don’t think it’s the main issue.
I was also told by a friend my catalytic converter could be bad so I am going to get an infrared temperature sensor and check the cat.
I’m worried if I take it to the dealership they’ll charge me to look at it and say they can’t find anything wrong. They did have it when all this started and nothing was brought up.

 

[joshuaeb09]

I do have a tow mode switch. When I activate it the truck shifts differently and goes back when it turns off.
I wouldn’t even know where to start on fuel trims and the like, but if it came to it I’m sure I could start learning and I might, just to know.
I’ve had the truck almost 2 years now and this didn’t happen last winter, so winter gas may be a problem, but I don’t think it’s the main issue.
I was also told by a friend my catalytic converter could be bad so I am going to get an infrared temperature sensor and check the cat.
I’m worried if I take it to the dealership they’ll charge me to look at it and say they can’t find anything wrong. They did have it when all this started and nothing was brought up.

I would start with the simple stuff that would effect MPG's being the IAT sensor, MAP sensor, and the O2 sensors. Depending on the mileage you might want to replace some of that stuff anyways as they can wear out over time.

 

[U&A]

winter gas.

Well said sir,

I loose a solid 2 mpg on winter blend.


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[huntergreen]

This would be the first time I have heard of winter gas causing a 4 or 5 mpg loss.

 

[joshuaeb09]

Well said sir,

I loose a solid 2 mpg on winter blend.


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I usually loose 2 at the most depending on conditions.

 

[Burla]

winter mileage goes down and thanks to our gov't they post why.

 

[John Casino]

I think I figured it out. Clogged/dirty injectors. Must’ve knocked something loose when they replaced the head. I did 3 consecutive injector cleaning treatments(the ones you pour into the tank) and I’m back up to 20mpg.
Thanks for the help. I have definitely realized I don’t know enough about my truck.

 

[Kap1]

I actually have the same issue with my 2013. I get about 15mpg on highway max and 12 in city. I think I can try the injector cleaning bottle to see if it may help? Anyone ?

 

[joshuaeb09]

I think I figured it out. Clogged/dirty injectors. Must’ve knocked something loose when they replaced the head. I did 3 consecutive injector cleaning treatments(the ones you pour into the tank) and I’m back up to 20mpg.
Thanks for the help. I have definitely realized I don’t know enough about my truck.

Could also be the intake being dirty as well. Lots of miles without a catch can and running cheaper fuel will contribute heavily to this. I prefer to do the full on induction service with the cleaner being run through the intake as well as an in tank additive every 20K mi or so. I use a dealer/shop product from a distributor that works really well, but I haven't seen it available at retail unfortunately. Something you can get off the shelf/over the counter would be like the seaform or gum out regane cans that come with the special straw for this purpose. That being said I also only run top tier fuels and regularly use an additive that lubricates, deals with the corn gas, and cleans to help keep everything running well.

 

[joshuaeb09]

I actually have the same issue with my 2013. I get about 15mpg on highway max and 12 in city. I think I can try the injector cleaning bottle to see if it may help? Anyone ?

Have you ever run a treatment, cleaned the TB and/or intake out ? If not and you're getting up there on the miles then more than likely it could very well help. Depending on the mileage you'll want to take care of both, preferably right before an oil change. There are a number of decent products you can pick up from your local parts store or order online.

Some of the readily available brands I've used in the past would be these in no particular order of preference.

Induction Spray :
https://seafoamsales.com/sea-foam-spray/
https://gumout.com/maintenance-aerosols/regane-direct-injection/

TB Cleaners :
https://www.crcindustries.com/products/throttle-body-air-intake-cleaner-12-wt-oz-05078.html
https://www.berrymanproducts.com/pr...l-carburetor-choke-and-throttle-body-cleaner/

Tank Additives :
https://www.redlineoil.com/si-1-complete-fuel-system-cleaner
https://gumout.com/fuel-additives/regane-complete-fuel-system-cleaner-12oz/
https://www.chevronlubricants.com/en_us/home/products/techron-complete-fuel-system-cleaner.html
http://championbrands.com/SpecSheet/Bowtie-4954I.pdf