Lost 4-5mpg after service

[MileHighRam11]

Same issue with my 2011. Had it in the shop for over two weeks to replace manifold bolts, camshaft, lifters, and gaskets. I was averaging 15.6 before service and now down to 12.3 after one full tank. Very odd.

 

[John Casino]

I’m back down to 15mpg again. It doesn’t downshift as much now though.
I usually only run chevron mid grade gas, but was 150miles from one and was empty so had to fill up at a small convenient store and that’s the tank I lost the mileage on. Going to do another treatment (injector and fuel system) into the tank once I find another chevron...when I get some down time I’ll try the induction spray and TB cleaner. Thanks.

 

[Frankwhoa]

Stay away from that store and especially their mid grade. Some of these stores mid grade rarely gets used and that little bit just sits in the pump going bad. I got stuck out in a boat once from a little small shops mid grade. Had enough condensation in the line to fill my carb with water.

 

[mlehn5]

have you considered that the shop may have cranked down your high end gears.....ala the +/- Gear shifter.
Maybe they have your highest available gear at 5 or 6.....and taking it up to 7 or 8 would get you back to where you need to be?....its an easy check and cheap solution if it works......just saying.

 

[John Casino]

I have 7th and 8th gear.

 

[JRitz187]

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.

What did you use? I have a '16 Ram 1500 and have been struggling at 13-14 MPG, I have a level and bigger tires but its still low compared to what I used to get. $50 on some pour in cleaners might help and is worth a shot anyway

 

[John Casino]

I used the STP brand fuel injector treatment

 

[John Casino]

Since I wrote this post I’ve driven about 1800 miles. I’ve found The issue comes and goes. This morning I drove 380 miles with only a 600ft. Elevation change and got 14mpg. The truck needed to downshift just to maintain speed even on flat straightaways and mileage was bad even on declines. I was stopped for an hour and a half and am 200 miles into the drive back. I’m getting 19-20mpg and it’s holding 8th even on inclines.

 

[joshuaeb09]

Since I wrote this post I’ve driven about 1800 miles. I’ve found The issue comes and goes. This morning I drove 380 miles with only a 600ft. Elevation change and got 14mpg. The truck needed to downshift just to maintain speed even on flat straightaways and mileage was bad even on declines. I was stopped for an hour and a half and am 200 miles into the drive back. I’m getting 19-20mpg and it’s holding 8th even on inclines.

How many miles does it have on it ? That sort of behavior sounds more like sensors that are working sporadically on their way out or are dirty. If one of your O2's got banged around by the dealer when they did the work it could also be damaged as they are somewhat sensitive. If you don't want to replace all the O2 sensors you could try cleaning them by soaking them in gasoline overnight to loosen up any crud that's on them and then hit them with electronics/sensor cleaner (My go to is usually CRC QD Electronic Cleaner). The CRC would also work on the MAP sensor if it happens to have a lot of junk on/in it from the PCV. Alternatively you could try something like one of those so called catalyst cleaners (Thinking the adds for Cataclean here which is just mostly solvent's) and then go take it for an Italian tune up rather than just driving it normally.

 

[indept]

Bottom line is he should still be under 3/36 and if not at least the 5/ 60 power train warranty so the dealer should be addressing this.

 

[John Casino]

I have 138,000 miles on the truck now, but I bought the 999,999 mile warranty. I have stopped and will be taking it into the dealer in the morning. Just hoping they don’t say they can’t find anything wrong...

 

[joshuaeb09]

I have 138,000 miles on the truck now, but I bought the 999,999 mile warranty. I have stopped and will be taking it into the dealer in the morning. Just hoping they don’t say they can’t find anything wrong...

You weren't kidding when you said you drive a lot for a work. You're over due for plugs unless you've already had them changed at the 100K interval or sooner. I'd probably push for them to check out the basic stuff like the O2 sensors, PCV, MAP sensor, Cat's, etc. Most modern 4 wire O2 sensors typically have a service life of around 100K, but sometimes will go longer or die sooner. They're also pretty sensitive to getting beat up. PCV's can also go bad after a while and cause gremlins to appear if they're just sticking at random rather than broken. The MAP sensors on the trucks can also degrade over time or go bad sending false manifold pressure readings. Being a speed/density motor the MAP sensor takes the place of a MAF sensor when working in conjunction with the IAT sensor. While rare to happen in a properly operating emissions system the cat's can also get plugged which would cause issue's all though that would be a consistent issue and you'd have a CEL illuminated. You could also have a vacuum leak somewhere, but since it's sporadic any vacuum issue would likely be that PCV as mentioned.

Hopefully they get it nailed down pretty quick for you. If they can't I'd invest a small amount of money in a scan tool that can log these parameters so you can nail it down yourself and then go back to the dealer and push for a fix. Sadly this is sometimes the only way to get things done with them.

 

[John Casino]

The dealership, of course, says everything is fine as far as sensors and fuel system go. They Also said their mechanic test drove my truck it doesn’t feel the vibration I feel from a bad u joint or something related...

 

[renfrick1]

After reading this thread I had my plugs replaced and added 2 bottles of injector cleaner. I got 19.5 mph on the hiway this morning!!! I’ve never gotten that. I usually see 14-15. Mind you it was raining and I was only doin 60-65. But I think plugs and treatment worked for better mileage


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