Need help… Crank/no start + Really bad MPG

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Rayyy

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2004 Vortec 5.3 4x4

It never, ever starts on first try. Cranks, but no start. However, starts right up on the second attempt every time.

Also, truck seems slightly sluggish. It still pulls at WOT, just seemingly not at 100% power.

MPG is a wopping 8.1MPG (confirmed by calculating manually using an MPG app too)… Even when I cruise around in town below 2,000rpm for the entire tank.

@ idle RPM
STFT 2.3+/-
LTFT +4.7 (bank 1) +6.2(bank 2)

@2500 RPM
STFT -4.7
LTFT +7.8 (both banks)


So far, I’ve replaced the plugs, wires, valve covers, intake air filter, MAF, brakes.

I’ll be adding some additives to the next tank to try to clean the fuel system and injectors, as well as replace the fuel filter.

Wondering if anyone has any idea of what else it could be?
 
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Fless

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I would replace the fuel filter and see what the fuel pressure looks like both key-on engine off, and engine running.

^^^ This. Test fuel pressure at the fuel rail. Use the standard KOEO test, as well as when it's running.

Based on your RPO codes you have a non-Flex Fuel LM7 engine.
 

RAMurphy

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As already been stated. Get a good reading on your fuel pressures and replace that fuel filter. Have you tried to turn the ignition to "on" for a 3-5 seconds (to build up fuel pressure) before cranking to see if that helps your first start. Before replacing my original fuel pump (290K miles), I was having a similar problem during initial start.
 

OR VietVet

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My girl's 2002 TrailBlazer is going thru that initial crank and no start or long crank before start. 3-5 seconds KOEO and then starts as normal. The problem is very intermittent. Lots of power. I have ran tests and know it is the bleed off of fuel pressure at the pump. Great pressure but bleeds down to about 30 psi in an hour and bleeds more the longer it sets.
 

OR VietVet

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By the way, I did not just assume the pump was the bleed off. I checked by pinching the fuel return line. I saw very slight clean area at fuel pressure regulator, like a fuel leak, and I replaced with a Genuine GM part.
 
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Rayyy

Rayyy

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My girl's 2002 TrailBlazer is going thru that initial crank and no start or long crank before start. 3-5 seconds KOEO and then starts as normal. The problem is very intermittent. Lots of power. I have ran tests and know it is the bleed off of fuel pressure at the pump. Great pressure but bleeds down to about 30 psi in an hour and bleeds more the longer it sets.
How is the MPG?

I don’t believe the 02 had the Average MPG in the cluster… but, there is an app called Fuely, which calculates for you and just requires to input odometer/fuel at each fill up.
 

OR VietVet

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How is the MPG?

I don’t believe the 02 had the Average MPG in the cluster… but, there is an app called Fuely, which calculates for you and just requires to input odometer/fuel at each fill up.
Not really worried about MPG. It is her around town vehicle, so she has a smaller vehicle to park easier and still carry loads in back. I have my 05 Z71 and she has a 1990 Chevy K2500 ext cab truck with a shell on it. Only has 128k miles on that truck and is as solid a rig as there is out there.
 

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