I have a 2007 Silverado LTZ 5.3 w/ Flex (never have run E85) and it takes awhile for it to start. i crank it over for a good 20-30 seconds then it finally struggles to start...then starts. once its started, it runs fine.

also, i have noticed that my avg mpg has gone from 16 to 12 since this started about 2-3 weeks ago.

There is a check engine light. I went to autozone and had them do their free code check, an it came back with "no codes"  

when it started doing this, its been every time...not just once n awhile. its every time i try to start it since the first time it did it to me.

any suggestions as to what it can be?

i know u got a bunch of miles...most likely due for a tune up...plugs and such

You definately have an electrical gremlin in that truck! Could be a possibility of a lot of things....I'm beginning to think fuel pump....gm fuel pump's tend to go out around 100k on them trucks....also the fuel filter is probably ready for service! Now question? You started having this issue when swapping to e85? Or are you still running 87? Your mileage going down is a solid indicator of the fuel filter and possibly the fuel pump....maybe tomorrow we can take a look at it, and I can get a real scanner on that thing and run some diagnostic tests!

Brad is the fuel pump making a humming noise?My buddy kind of had the same problem but his truck is not a flex.If the fuel pump is humming it might need to be replaced.you should be able to here it while running by the fuel tank.

I just emailed the old man about this. We had exactly the same thing on his old Van with a 4.3 Vortec a few years ago, and I'm struggling to remember the whole week long ordeal.  

While I was back there, I was voted to figure it out.

Immediately thought injectors, but that wasn't it. (Bigger problem in the northeast in the winter, beleive me, fugger would drag the battery down but QUICK).

As I recall there was an electronic valve, I'm still searching the internet for what it is/was, that was in the rear of the intake manifold that I changed out. Still wasn't the problem, but in doing this we found a wiring problem with that valves harness and plug. Cut the wires and crimped in some new Molex connectors, That fixed it then.

Did the same thing a few months later, and as already pointed out, was the in tank fuel pump.

Ray

where is the fuel pump located? i bet somewhere retarded like in the tank 

BINGO! and they're only good for about 75K miles, guess where the fuel filter is? Yep, attached to the pump, also only good to about 75K. Have fun with that, it requires dropping the tank, I did mine on my 99 Silverado, and I'll never do another one!

Yep, pump is in tank. Not too hard to change out. Bout 2 hours.

disconnect battery, empty out tank as much as possible then put floor jack or strong buddy and start undoing the strap bolts. lower it slowly until you can reach the connectors, disconnect elec wiring and fuel lines lower it rest of the way. Undo retaining ring and carefully pull out pump. swap out pump and re-install. PITA, but not too bad.

Should definitely be covered, but call em to double check. 

calling...

of course they cant tell me anything over the phone. 

BINGO! and they're only good for about 75K miles, guess where the fuel filter is? Yep, attached to the pump, also only good to about 75K. Have fun with that, it requires dropping the tank, I did mine on my 99 Silverado, and I'll never do another one!

This makes me oh so confident on my 06 Trailblazer with the 5.3!

BINGO! and they're only good for about 75K miles, guess where the fuel filter is? Yep, attached to the pump, also only good to about 75K. Have fun with that, it requires dropping the tank, I did mine on my 99 Silverado, and I'll never do another one!

sorta funny my filter was on the frame rail! on my 2000...i had a 5.3 truck, but not that body style, wonder how many changes they have made? im guessing because of the e85 it made the pump more expensive! also there are two ways to do the fuel pump and believe it or not option #2 is alot easier just takes a little help...

option one drop the tank, and then pull the pump

option two take the bed off! walah it's right there!

injector cleaner for next few tanks to start......and clean throttle plate

actually this stuff works ok....there is this stuff that you can buy that you can actually tie into the fuel rail there's a provision there kinda like charging you ac system....anyway you get a can that attatches to the fuel rail, and that's what really cleans the injectors...also the MAF "mass air flow" sensor could probably use a good cleaning!

like i said there's ways to look at stuff going on in your motor just gotta make sure the motis is up to date, and we can scan it, and that thing will tell you more about your vehicle then you want to know!

so when i turn on the ignition, its dead silent. no sign of the fuel pump kicking on.

i check the fuse...its good.

where is the fuel pump located? i bet somewhere retarded like in the tank 

this is what i wanted to recommend to ya...anyway give me a call later