I have a 2004 5.3 flex fuel engine.

2 days ago my girlfriend called me and told me the truck would not start. A buddy went over and looked at it for me and told me he had to cycle the key a few times and it then started. It had an 1/8 of a tank and was downhill and hadn't been started for two days. It's been fine since.

I have noticed only about 13mpg highway lately and it seems to have little power through 1st and 2nd gear normal driving and it cackles a lot through the exhaust. If i floor it, it seems like it misses a gear then gets going after that, but the tranny seems like its not slipping.

Tested the pressure with key on, engine off and pressure was at 50psi then dropped to 45. engine on it was at 45psi and when given throttle it drops to 40psi. Is this normal on a flex fuel 5.3? no leaks anywhere and regulator is dry. Is this a sign of a failing pump? also, do i have a return style fuel system?

sorry for the lengthy post..

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Alright guys/gals, very confused here.

First, I have determined for myself that i have a return style fuel system.

Second, i have determined that the Flex-Fuel 5.3s have a Fuel pressure regulator that doesn't allow as quite as high fuel pressure as on non-flexFuel engines...about 45-52psi rather than the normal 55-60psi or so

So i apologize for not using "search"..

SO... I went to get new pressure readings after I schooled myself...

With the key ON, engine OFF, my pressure does not build unless I cycle the key on and off and even then it only builds about 5-10psi at a time, but does not drop rapidly. Weird...
With the engine ON and idling, my pressure holds steady around 45psi and dips to 40psi with more throttle. Regulator is dry and does not have an overwhelming smell of fuel and the pressure increases to about 52psi with the vacuum line OFF the regulator. Getting odd...

So, to sum it up... when I turn the key and crank the engine, it starts up the first time (most of the time) but takes a second longer. If I have to try cranking again, it "chugs" to life. If I just turn the key to ON and engine OFF, the pump will not make sufficient pressure. I do have intermittent 'surging' if I let the truck idle forward at a light and a hesitation when giving enough throttle to downshift and accelerate.

Truck has 212/218 comp cam, tune, CAI, and LTs @ 172k miles.
I'm thinking pump is on the way out, and soon. Can anyone back up my assumptions before I throw dollar bills at my "Hoe"?

 

Did you check change your fuel filter? Maybe when the truck was low on fuel you sucked up some dirt from the bottom of the tank.

 

Sounds like a pump going out to me...

 

Yeah I took the filter out and it seemed fine. The regulator was dry and fuel pressure rose as normal when I disconnected the vacuum line. Can't find a kink or leak anywhere. Just confused as to why very little pressure when key is on and engine off but normal pressure at idle

I'm going to assume it's the pump getting weak an maybe a check valve issue. Maybe clogged up filter sock/strainer?

I just wanted to get some opinions before I pulled the trigger on a pump. I'll most likely do that this weekend and I'll reply with results.