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Sudden loss of fuel economy - 2014 Chevy Silverado 5.3 LT - dropped 7m


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Top tier...I dont have loyalties and fill up all over. In my area top tier is sold by holiday and super america gas stations. Have tried two different oils over past months. Full synthetic and also a blended ow-20. currently have dexos ow-20 the dealership put in.

 

@65 mph on my gauges it states I am getting qbout 15mpg. I can hand calculate and it is accurate. I used to get over 500 miles per tank and now getting about 390 per tank, approximatl

Eh. What area do you live in? Also what octane are you running? I am hounding on this a bit because believe it or not, I've noticed fuel economy differences in the brand of gas I use. Oh sure it's all the same when it is refined, and then that various manufacturers ad pack is added at the fuel terminal, but believe it or not when I stick to Shell or Chevron or Phillips 66/Conoco vs say Diamond Shamrock or Costco, or Valero or Sinclair, I do notice I get a slightly better MPG in my gas vehicles. Now those are ALL top tier stations, so they meet the top tier criteria for detergent additives to keep things clean, but some brands like Shell take it a step further and add some things to their premium 91/93 Octane fuels as well, which I believe is where I am noticing the difference. More so on modern vehicles with direct injection, when running premium. I am pleased to see that you had a BG induction service done. But if it were me, I'd still run a can of BG44k thru the fuel every 6 months with a DI engine.

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Could this possibly be an issue with the 5.3 dod? Displacement on Demand V-4 to V-8 mode? It almost sounds like it's not going into 4 cylinder mode and behaving as a full time V8.. The only way you'll get the higher MPGs is with it going into V4 mode while cruising. Did the fuel economy drop suddenly or was it gradual? Was there any software updates done to your truck right before the fuel economy began to drop?

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I'd wait and test this last round first. Give it couple of weeks. Then if bad fuel mileage comes back I'd have a look at the cats. Because you want to know what the solution was.... If you do too many things at once then you don't know what cured your problem just like you don't know now if it was the cleaning or the ebrake that helped.

 

 

My OBDII tool is an APP on my Android called Torque Pro ( $3.99 USd ) best dang $5 I ever spent ( $4.99 Cdn ) You just need a compatible bluetooth adapter and you're good to go.

 

2015-02-14%2011.58.35_zpsuupz6f08.jpg

 

I got this one but get which ever one is compatible with the APP. Some people don't like to buy Chinese but I'm not one of them, they make everything any way so why pay 10 times the price for the same item.

 

http://www.banggood.com/fr/HHOBD-ELM327-Car-Bluetooth-OBD2-Auto-CAN-BUS-Scanner-Tool-Android-p-913030.html?rmmds=search

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The ecotech3 engines arent what i consider normal compression engines. Even the 5.3 has 11:1 compression. That isnt what I call low compression.I run 93 octane gas in mine and do get slightly better gas mileage over 87. I also get lots of pinging in the summer on 87 since its always super hot here.

 

Not that any of that has to do with that big of a mileage drop but its somthing to consider. Specially if the price doesn't outweigh benefit.

 

The only other issue is with DI engine unless your fogging through the intake manifold, these cleaners arent touching the back of the intake valves.

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Sunoco is not a top tier fuel. :nono:

Top tier refers to the detergent additives, it's doesn't make a difference for fuel economy (at least not for 1 tank on a 1 yr old truck). Besides my usual gas station is a Speedway due to convenience and they also are not Top Tier.

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UPDATE: Today I am back to poor mpg now getting 14mph on highway at 65mph. On a 300 mile road trip from chicago to minneapolis.

 

This is bizzare. After the BG induction cleaning on Friday, I took a test drive for 30 miles freeway and got 20mpg.

 

Same route leaving today and Im getting 14 mpg. its much warmer today 50 degrees F

 

???

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UPDATE: I got 13 mpg on the 300 mile ride home from chicago. Now I think its the emergency or parking brake producing drag.

 

I have tried to disengage, rengage, disengage different times, but I feel like there is drag at highway speeds. The e brake does work when engaged.

 

Is that possible? For the e-brake to cause drag, even though it is disengaged? Could it be too tight and some sort of drag on the caliper?

 

No smoke, no vibration.

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I don't know if I could buy the brake issue- with the amount of driving you've done, the brake pad would have been worn down a long time ago and drag would not be a factor.

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The eBrake would have overheated and burnt up and would not be working anymore; at least not enough to apply enough drag to hurt you mileage. I'll go with the throttle body cleaning as the answer which probably cleaned your intake valves too. Congrats on getting it back into shape.

Edit: sorry I missed the last posts. Hope you get it fixed.

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I don't know if I could buy the brake issue- with the amount of driving you've done, the brake pad would have been worn down a long time ago and drag would not be a factor.

X2

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It's normal in cold areas of the country to see 10-15% drop in mileage in the Winter due to the blend. Like you, I was also getting 21-22mpg in the Summer. Just got back from a 3000 mile road trip..................When I was driving in the warm/hot weather in Florida, Georgia and SC; I was getting over 20mpg................not 22 like at home, but there were times I was running 80mph+ and/or bucking the wind. I lockout V4 with the Range device also.

 

When I left to come home from Virginia on this trip, I drove into a 15mph headwind the whole way home. Filled up in VA, and drove to Indiana before filling.............averaged about 18mpg. When I filled in Indiana, the temp was 3*F and dropped to -4*F in the 200 miles home from there. The dash display never got above 17mpg on that tank due to the cold. My display reads about .3-.5mpg high when I hand calculate mileage...............so I was in the 16's.

 

Your drop seems high though. Do you do long warm ups?? Could it be a sensor like..................IAT or O2 or MAP???

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