Sudden loss of power and mpgs

[MarcuM]

I got a 2016 5.3 6sp 3.42 crew cab and I drive a insane amount of miles working out of state wv to ga every week 64kmiles since new in February 2017 

 

i avg 25-30mpg depending on speed limits on my trips until this past ride home I’ve lost 4-8mpg and the truck feels like it’s lost some hp or very similar to a 4.8l motor having to keep my foot in it more and more 

 

 

I’ll be cruising in v4 mode and come to a slight hill and before I know it I’m 50-75% in the throttle and it’s still lugging 6th gear until eventually I will have my foot in it enough to where it has to hit passing gear to catch back up to the speed limit 

 

 

On back roads it worse 

i can keep a even 10% throttle and in v4 mode the truck will slow down 10mph compared to leaving the truck in m5 and running 10% throttle it’s great other then high rpms 

 

from a dead stop it runs great up to cruise speed but something is dragging it down on top end 

 

any help would be appreciated I just don’t understand how 64k miles of perfect then all of the sudden crap lol 

 

 

thanks matt 

[FIREBLADE74]

On my 17 I’ve noticed needing more throttle to keep it going. Would love to hear some feedback. 

[m3n00b]

Carbon build up?

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[MarcuM]

It does idle a lot !

since being off for week of x mass I’ve filled up twice with 93 octane and used Techron cleaner and changed tranny oil + filter still nothing changed 

[MarcuM]

I’ve read on here about seasonal gasoline in the colder states that is why I first thought fuel then thought torque converter was sticking in 1:1 so changed trans fluid ( it was due anyway) 

now I don’t know what next step is ?

I think if I get rid of the v4 mode it would fix it but I want to know why before I do 

[FIREBLADE74]

Only got 3k miles so it can’t be carbon buildup at least I hope not. The lack of power happens in v8 mode. Could be the seasonal gas but I’m in SC. 

[swathdiver]

I would consider your use of the truck severe service and change all the fluids and plugs and wires and such at 50k miles or less.  Mine is much older and it idles a lot too and one of the catalytic converters does not like that.

[MarcuM]

Yea I guess your right 

even though it’s never been in 4x4 or towed anything it’s still got 2100hrs on 63kmiles

so do plugs and wires and coil packs??

[MarcuM]

I was just doing some reading and didn’t see a lot about the new trucks but can I use the ngk tr55 plugs in my truck ?

[Nanotech Environmental]

5 hours ago, MarcuM said:

I was just doing some reading and didn’t see a lot about the new trucks but can I use the ngk tr55 plugs in my truck ?

I wouldn't spend any money on plugs, coils, wires, or anything else. until you are sure what the issue is. The plugs on these engines will easily go well over 100k miles, in fact they will go 200k miles. As will the rest of the spark system. 

You're gonna have to start going thru things one by one to see what is happening here, else you risk just wasting a bunch of cash. Don't replace things unless you're absolutely certain they are the problem.

I suggest checking the following things-

Do a full computer scan- what you describe should show up in a scan if it's a spark related issue.

Check spark train- plugs, coils etc.

Check battery and alternator voltage

All aspects of the intake tract, incl valves

Exhaust & cats

Check for sticking brakes (not likely with the age of the vehicle, but not impossible either)

Transmission issue?

 

 

[cossack]

Cold weather will do that, plus the winter time gasoline mix might contribute to that too.

 

[Sierra706]

Cold air is denser, harder to push through especially at highway speeds. Combine that with winter gas and the longer period it takes to warm up all your fluids and drivetrain components. I’ve gone from averaging 17 to averaging 12 with no change in driving style other than a 10 minute remote start.


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[swathdiver]

I don't think you'd need to replace the coils.  I would stick with factory plugs and wires unless you have time to experiment and measure results.  With the previous 2 generations of trucks, GM changed the plugs and more than a few people noticed that their mileage degraded over time.  When they changed back to the old part number, all was well again.  There were no misfires or check engine lights.  I suspect this may be mine own case.  Dense air is cooler and allows an engine to make more power and run more efficiently.  Thirty or so years ago my buddies and I experimented with different plugs in our muscle cars.  When we used the then new NGK Splitfires, they gave us about 5 more horsepower through the traps but cost 3 miles to the gallon.  So unless I wanted to squeeze every last drop of power out of the motor, just kept the stock plugs in.

 

I live in the south and have no idea what winter blend fuels are or even if we get them down here.  I do however, notice very definite gains or losses by using different grades of fuel and even among different stations.  If I want 8 mpg I'll go to Sam's Club or Cumberland Farms and pump in their 87 octane.  But if 16 mpg is more to my liking, I'll stick with 93 from Mobil.  Chevron is close, Sunoco has fallen off and several of our autos have never ran well on Shell.

 

It would be nice to data log your drive and see what's going on.  I can do this with my Tech2 and AutoCal but you would need the MDI and GDS2 software and a laptop I think.  The AutoCal might work as well but not sure, have to check with BlackBear.  

 

  

[acc412]

I agree with the Cold weather and winter blend statement. I have noticed this also in my '16 5.3.

[Grumpy Bear]

A bit more than a year of Pepper's fuel usage history. The yellow twelve tank moving average goes either side of the lifetime calculated average. Winter results are below the average and Summer results above. Blue is individual tanks by hand calculation. Note the range peak to peak, winter to summer in the scale on the right. It's quite large. I live in up state Illinois. Notice the brevity of the winters length of line. I don't drive her much in the winter. Takes to long to warm her up. Trans temperature for example can take nearly the entire 180 mile plus distance to dads to reach full heat on a cold winter day.  

 

Even my 40 mpg Honda's rarely see much over 32 mpg in the winter.