Sudden drop in mpg, 2007 Silverado 1500 2wd classic extended cab WT, V

[Robur]

I have a 2007 Silverado 1500 2wd classic extended cab WT, V8 4.8L.

It is this weird last-of-the-classic line when the truck was sold as 2007, but it is really 2006.

Anyhow, I have been driving this truck since 2006, a good 113 000 miles, and I used to get around 320 mpg out of a full 26 gallons tank. All of the sudden, I cannot go beyond 260 miles out of a full tank. We all know we don't drive them for the fuel economy, but to haul stuff. I occasionally tow my boat with it, but it seems to me a big drop on the fuel economy.

Tires are the same as I always had, 265/70/R17, I keep them inflated and balanced, recently did a full alignment and replaced some steering parts.

Someone recommended me to replace spark plugs and air filter, so I did. I replaced the stock 41-985 with ACDelco 41-962 Platinum. And got a new ACDelco A3181C Air Filter. No change.

I bought an OBD scanner, even though I don't have any check engine light, but I cannot find any error codes registered, or anything off.

The truck is stock except for the cruise control that I added back in 2007( GM part), power windows and power locks. I have no idea what may cause the mpg to drop so much.

Thanks for the input on this topic, any suggestions are really appreciated.

[elchilero53]

113K miles? That isn't very much. Several thoughts:

 

Could the ignition wires need replacement?

Each plug has its own coil. Could you have a bad coil(s)? (That happened to me with a company truck. Once replaced, the problems went away)

Tranny issues?

Have your reprogrammed the computer lately?

Could you need to reset your system or your tranny programming?

Fuel injector issues?

[sporty061200r]

Assuming your mileage number is correct 320 miles divided by 26 gal you were only getting 12.3 mpg to begin with that itself is poor, now your new numbers are and even 10 mpg for a truck thats not hatefull if your pulling a boat ECT. I would fill it all the way up reset the trip and throw a gas can in the bed and run it until its out.. then you may get a more accurate mpg.. you may be trying to fix something that's not broke

 

 

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[diyer2]

Assuming your mileage number is correct 320 miles divided by 26 gal you were only getting 12.3 mpg to begin with that itself is poor, now your new numbers are and even 10 mpg for a truck thats not hatefull if your pulling a boat ECT. I would fill it all the way up reset the trip and throw a gas can in the bed and run it until its out.. then you may get a more accurate mpg.. you may be trying to fix something that's not broke

 

 

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Disagree. Just hand calculate your mileage.

Stop running your gas tank so low, hard on the fuel pump. Gas cools and lubricates the fuel pump.

Did you put new wires on it? Use OEM wires.

Run some fuel cleaner in it. I like Sea Foam.

[Robur]

Thank you guys for all responses, I really appreciate it.

elchilero53 I will follow-up and change my ignition wires. I am OCD about OEM parts, especially for core functionality, I know how expensive cheaper parts can be in the long run. My regular use for the truck is just to drive to work, the mileage that I posted is without the boat.

I have never reprogramed the computer. The fuel injectors may be something to look into, is there any way to diagnose them?

sporty061200r I usually reset the trip computer for every time I fill up the tank, that is how I know that the gas mileage went down. After having issues with an O2 sensor on a car I used to own, I got into doing that.

diyer2 Thank you for the advice. I try not to ever get the reserve light on, although happens sometimes. I will give Sea Foam a try.

I will keep y'all posted on progress.

[txab]

O2 sensors may be getting a bit lazy. Have you cleaned your MAF with the proper cleaner. Might also try disconnecting and reconnecting battery and note if any mileage changes

[Robur]

Thank you txab. I will definitely test the MAF, and give the batt a disconnect to see if anything changes.

[Mike GMC]

I agree with running some fuel system cleaner. I like BG44K. You might also look into changing the tranny fluid and differential fluid. If you have a fuel filter, change it after the tank full of cleaner.

[Robur]

Hey Mike, thank you for replying. This truck has the fuel filter integrated inside the sender unit in the gas tank. No inline filters. I will try the cleaner.

[diyer2]

Sea Foam $7 at Wally World, BG 44K $30. Used it before finding Sea Foam.

You decide, both good products.

[Bad Bowtie2]

I like what everyone has said.

 

New AC Delco wires & upper O2 sensors, new fluids, and start using Chevron's Techron fuel additive at each oil change.

[calgator73]

Injector leak test.

 

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[Robur]

Thank you for your reply Bad Bowtie 2. I am filling up the tank today, I already got the SeaFoam, so will give it a shot. As a side note, I have been using fully synthetic oil since 50 000 miles. I cannot do much during the week truck-wise, got to wait for the weekend.

[sefiroxx]

Pull history codes. Typical large fast mpg drop is usually sensor or injector related. Slow drop (many years) is engine wear.

 

Start with O2 sensor, tps and mass flow. A good scanner will be able to give the readings from these sensors. Injector could get stuck open - use a mechanics stethoscope (metal stick connected to ear insert) - touch it to reach injector and listen for the tick, tick, tick

 

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[Robur]

Thank you Sefiroxx and Calgator73. I got a mechanics stethoscope, all injectors seem to be clicking. I am some 70 miles down on the tank with the seafoam, I will keep posting on how it goes. I haven't check on the O2 sensor, tps and mass flow, if it ever stops raining, I will