Bad mileage for 5.3 Silverado

[trentkoch123]

Hello, I have a 2001 Chevy Silverado 2500HD, It has a 5.3L V8 Vortec engine with 288,000 miles on it.  It has 265/75/R16 AT tires, Things that are original include 6/8 ignition coils, MAF sensor, fuel injectors, serpentine belt, ect sensor (ive heard of problems?)   Things that have been done to the truck since I got it include Radiator and water pump, hoses, heater hoses, Spark plugs and wires, fuel pump and O2’s in October 2017. 2 new ignition coils (The other 6 are stock) Oil changes/new air filters, Valve cover gaskets, (Used Throttle body cleaner and MAF cleaner about 1.5 years ago)

 

When I 1st bought the truck in late 2016 was getting around 13-15 hwy which was good for me at the time. About 6 months in, the fuel economy started to decline, though it was not overly concerning to me yet, but within the last 6 months (around September of 2019) it took a hard hit. What was a decent economy, I only get 9 or 10 miles a gallon on the freeway, and don’t even get me started about the atrocity that is city driving. However, I have noticed that my Long-Term Fuel Trim on both banks is anywhere from 14-18% no matter when I check it, hot or cold, idling or at 2000RPM. No one has been able to give me any direction on how to recover any mpg's so far. I use the truck for work daily, I do a lot of driving, but still, it shouldn’t be so low! I just need some guidance here, as to where to (re)start as for fixing this thing.  Thank you so so much if anyone has any types of input. Please help! somebody!

 

Thank you

[Jsdirt]

I thought mine was bad on gas. That's the worst I've seen! What gearing have you got? With 3.73's, I got 18 when the truck was brand new, then it settled to around 16 for years, but now I'm in the 14-15 range. Flex fuel engine, so I have to do a Fuel Composition Reset quite often.

 

The 800 series trucks were much better built than the 900s as far as quality goes - that said, the 900's are known for injectors sticking open not too long after 100k miles in alot of cases (and there have been problems right out of the gate with the brand new ones - high pressure direct injection -  but I digress).

 

At your mileage, you could be due. An injector balance test with a bi-directional scan tool and a pressure gauge will tell the tale. If that's the case, you don't have to go new - there's quite a few companies out there that clean, test, and rebuild them if needed. This particular one here I found on a professional auto technician's forum, recommended by one of it's members: https://www.mrinjectorparts.com

 

Also, depending on the brand of o2 sensors, those could be suspect as well (upstream only). Denso, or Delco are the only ones I'd run. Watch them closely on a scan tool set to graphing. 

[mjm-1957]

That truck should have a 6.0 in it not a 5.3. Send me the last 8 of the vin and I can look it up and see what you are working with.

[tlaw91]

Intake gaskets to start. But you’re working with a well worn 6.0, so don’t be expecting miracles lol

-Friendly neighborhood GM tech


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